Author: "Hviid S" / Publisher: univ maryland, dept astron, college pk, md 20742 usa. - Searchworks@Jio Institute Digital Library Search Results

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81 results on '"Hviid S"'

1. Tensile strength of 67P/Churyumov-Gerasimenko nucleus material from overhangs

Author: Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, Shi, X., Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, and Shi, X.
Abstract: We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features and the implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the similar to 10-100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km)., Correction in: Astronomy & Astrophysics, 614:C2 (2018), DOI: https://doi.org/10.1051/0004-6361/201732155e
Published: 2018
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2. Tensile strength of 67P/Churyumov-Gerasimenko nucleus material from overhangs

Author: Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, Shi, X., Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, and Shi, X.
Abstract: We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features and the implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the similar to 10-100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km)., Correction in: Astronomy & Astrophysics, 614:C2 (2018), DOI: https://doi.org/10.1051/0004-6361/201732155e
Published: 2018
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3. Tensile strength of 67P/Churyumov-Gerasimenko nucleus material from overhangs

Author: Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, Shi, X., Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, and Shi, X.
Abstract: We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features and the implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the similar to 10-100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km)., Correction in: Astronomy & Astrophysics, 614:C2 (2018), DOI: https://doi.org/10.1051/0004-6361/201732155e
Published: 2018
Full Text: View/download PDF

4. Tensile strength of 67P/Churyumov-Gerasimenko nucleus material from overhangs

Author: Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, Shi, X., Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, and Shi, X.
Abstract: We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features and the implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the similar to 10-100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km)., Correction in: Astronomy & Astrophysics, 614:C2 (2018), DOI: https://doi.org/10.1051/0004-6361/201732155e
Published: 2018
Full Text: View/download PDF

5. Tensile strength of 67P/Churyumov-Gerasimenko nucleus material from overhangs

Author: Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, Shi, X., Attree, N., Groussin, O., Jorda, L., Nebouy, D., Thomas, N., Brouet, Y., Kuehrt, E., Preusker, F., Scholten, F., Knollenberg, J., Hartogh, P., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Fornasier, S., Fulle, M., Gutierrez, P. J., Guettler, C., Hviid, S., Ip, W. -H, Kovacs, G., Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Lowry, S., Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Toth, I., Tubiana, C., Vincent, J. -B, and Shi, X.
Abstract: We directly measured twenty overhanging cliffs on the surface of comet 67P/Churyumov-Gerasimenko extracted from the latest shape model and estimated the minimum tensile strengths needed to support them against collapse under the comet's gravity. We find extremely low strengths of around 1 Pa or less (1 to 5 Pa, when scaled to a metre length). The presence of eroded material at the base of most overhangs, as well as the observed collapse of two features and the implied previous collapse of another, suggests that they are prone to failure and that the true material strengths are close to these lower limits (although we only consider static stresses and not dynamic stress from, for example, cometary activity). Thus, a tensile strength of a few pascals is a good approximation for the tensile strength of the 67P nucleus material, which is in agreement with previous work. We find no particular trends in overhang properties either with size over the similar to 10-100 m range studied here or location on the nucleus. There are no obvious differences, in terms of strength, height or evidence of collapse, between the populations of overhangs on the two cometary lobes, suggesting that 67P is relatively homogenous in terms of tensile strength. Low material strengths are supportive of cometary formation as a primordial rubble pile or by collisional fragmentation of a small body (tens of km)., Correction in: Astronomy & Astrophysics, 614:C2 (2018), DOI: https://doi.org/10.1051/0004-6361/201732155e
Published: 2018
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6. The global meter-level shape model of comet 67P/Churyumov-Gerasimenko

Author: Preusker, F., Scholten, F., Matz, K. -D, Roatsch, T., Hviid, S. F., Mottola, S., Knollenberg, J., Kuehrt, E., Pajola, M., Oklay, N., Vincent, J. -B, Davidsson, Björn, A'Hearn, M. F., Agarwal, J., Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Ip, W-H, Jorda, L., Keller, H. U., Koschny, D., Kramm, J. R., Kueppers, M., Lamy, P., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Naletto, G., Rickman, H., Rodrigo, R., Sierks, H., Thomas, N., Tubiana, C., Preusker, F., Scholten, F., Matz, K. -D, Roatsch, T., Hviid, S. F., Mottola, S., Knollenberg, J., Kuehrt, E., Pajola, M., Oklay, N., Vincent, J. -B, Davidsson, Björn, A'Hearn, M. F., Agarwal, J., Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Ip, W-H, Jorda, L., Keller, H. U., Koschny, D., Kramm, J. R., Kueppers, M., Lamy, P., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Naletto, G., Rickman, H., Rodrigo, R., Sierks, H., Thomas, N., and Tubiana, C.
Abstract: We performed a stereo-photogrammetric (SPG) analysis of more than 1500 Rosetta/OSIRIS NAC images of comet 67P/ChuryumovGerasimenko (67P). The images with pixel scales in the range 0.2-3.0 m/pixel were acquired between August 2014 and February 2016. We finally derived a global high-resolution 3D description of 67P's surface, the SPG SHAP7 shape model. It consists of about 44 million facets (1-1.5 m horizontal sampling) and a typical vertical accuracy at the decimeter scale. Although some images were taken after perihelion, the SPG SHAP7 shape model can be considered a pre-perihelion description and replaces the previous SPG SHAP4S shape model. From the new shape model, some measures for 67P with very low 3 sigma uncertainties can be retrieved: 18.56 km(3) +/- 0 : 02 km(3) for the volume and 537.8 kg/m(3) +/- 0.7 kg/m(3) for the mean density assuming a mass value of 9 : 982 +/- 10(12) kg.
Published: 2017
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7. Seasonal erosion and restoration of the dust cover on comet 67P/Churyumov-Gerasimenko as observed by OSIRIS onboard Rosetta

Author: Hu, X., Shi, X., Sierks, H., Fulle, M., Blum, J., Keller, H. U., Kührt, E., Davidsson, B., Güttler, C., Gundlach, B., Pajola, M., Bodewits, D., Vincent, J. -B, Oklay, N., Massironi, M., Fornasier, S., Tubiana, C., Groussin, O., Boudreault, S., Höfner, S., Mottola, S., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Gicquel, A., Gutierrez-Marques, P., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Küppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Thomas, N., Hu, X., Shi, X., Sierks, H., Fulle, M., Blum, J., Keller, H. U., Kührt, E., Davidsson, B., Güttler, C., Gundlach, B., Pajola, M., Bodewits, D., Vincent, J. -B, Oklay, N., Massironi, M., Fornasier, S., Tubiana, C., Groussin, O., Boudreault, S., Höfner, S., Mottola, S., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., El-Maarry, M. R., Gicquel, A., Gutierrez-Marques, P., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Küppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., and Thomas, N.
Abstract: Context: Dust deposits or dust cover are a prevalent morphology in the northern hemi-nucleus of comet 67P /Churyumov-Gerasimenko (67P). The evolution of the dust deposits was captured by the OSIRIS camera system onboard the Rosetta spacecraft having escorted the comet for over two years. The observations shed light on the fundamental role of cometary activity in shaping and transforming the surface morphology. Aims: We aim to present OSIRIS observations of surface changes over the dust deposits before and after perihelion. The distribution of changes and a timeline of their occurrence are provided. We perform a data analysis to quantify the surface changes and investigate their correlation to water activity from the dust deposits. We further discuss how the results of our investigation are related to other findings from the Rosetta mission. Methods: Surface changes were detected via systematic comparison of images, and quantified using shape-from-shading technique. Thermal models were applied to estimate the erosion of water ice in response to the increasing insolation over the areas where surface changes occurred. Modeling results were used for the interpretation of the observed surface changes. Results: Surface changes discussed here were concentrated at mid-latitudes, between about 20 degrees N and 40 degrees N, marking a global transition from the dust-covered to rugged terrains. The changes were distributed in open areas exposed to ample solar illumination and likely subject to enhanced surface erosion before perihelion. The occurrence of changes followed the southward migration of the sub-solar point across the latitudes of their distribution. The erosion at locations of most changes was at least about 0 : 5 m, but most likely did not exceed several meters. The erosive features before perihelion had given way to a fresh, smooth cover of dust deposits after perihelion, suggesting that the dust deposits had been globally restored by at least about 1 m with eject
Published: 2017
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8. Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

Author: Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M. A., Vincent, J. -B, Tubiana, C., Guettler, C., Preusker, F., Scholten, F., Mottola, S., Hasselmann, P. H., Feller, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, Björn J. R., Debei, S., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., Masoumzadeh, N., Oklay, N., Kolokolova, L., Sierks, H., Fornasier, S., Barucci, M. A., Vincent, J. -B, Tubiana, C., Guettler, C., Preusker, F., Scholten, F., Mottola, S., Hasselmann, P. H., Feller, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, Björn J. R., Debei, S., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., and Thomas, N.
Abstract: Aims. We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods. We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results. We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.
Published: 2017
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9. Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past

Author: El-Maarry, M. Ramy, Groussin, O., Thomas, N., Pajola, M., Auger, A. -T, Davidsson, B., Hu, X., Hviid, S. F., Knollenberg, J., Guettler, C., Tubiana, C., Fornasier, S., Feller, C., Hasselmann, P., Vincent, J. -B, Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Keller, H. U., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., Fulle, M., Gutierrez, P. J., Hofmann, M., Ip, W. -H, Jorda, L., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Yi, Moreno, J. J. Lopez, Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Shi, X., El-Maarry, M. Ramy, Groussin, O., Thomas, N., Pajola, M., Auger, A. -T, Davidsson, B., Hu, X., Hviid, S. F., Knollenberg, J., Guettler, C., Tubiana, C., Fornasier, S., Feller, C., Hasselmann, P., Vincent, J. -B, Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Keller, H. U., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., Fulle, M., Gutierrez, P. J., Hofmann, M., Ip, W. -H, Jorda, L., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Yi, Moreno, J. J. Lopez, Marchi, S., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., and Shi, X.
Abstract: The Rosetta spacecraft spent similar to 2 years orbiting comet 67P/Churyumov-Gerasimenko, most of it at distances that allowed surface characterization and monitoring at submeter scales. From December 2014 to June 2016, numerous localized changes were observed, which we attribute to cometary-specific weathering, erosion, and transient events driven by exposure to sunlight and other processes. While the localized changes suggest compositional or physical heterogeneity, their scale has not resulted in substantial alterations to the comet's landscape. This suggests that most of the major landforms were created early in the comet's current orbital configuration. They may even date from earlier if the comet had a larger volatile inventory, particularly of CO or CO2 ices, or contained amorphous ice, which could have triggered activity at greater distances from the Sun.
Published: 2017
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10. Multivariate statistical analysis of OSIRIS/Rosetta spectrophotometric data of comet 67P/Churyumov-Gerasimenko

Author: Perna, D., Fulchignoni, M., Barucci, M. A., Fornasier, S., Feller, C., Deshapriya, J. D. P., Hasselmann, P. H., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., Deller, J., De Cecco, M., El-Maarry, M. R., Fulle, M., Groussin, O., Gutierrez, P. J., Guttler, C., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuhrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Oklay, N., Thomas, N., Tubiana, C., Vincent, J. -B, Perna, D., Fulchignoni, M., Barucci, M. A., Fornasier, S., Feller, C., Deshapriya, J. D. P., Hasselmann, P. H., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., Deller, J., De Cecco, M., El-Maarry, M. R., Fulle, M., Groussin, O., Gutierrez, P. J., Guttler, C., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuhrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Oklay, N., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: Context. The ESA Rosetta mission explored comet 67P/Churyumov-Gerasimenko in 2014 2016, following its target before and after the perihelion passage on 13 August 2015. The NAC camera of the OSIRIS imaging system allowed to map the nucleus surface acquiring images with different filters in the visible wavelength range. Aims. Here we study the spectrophotometric behaviour of the nucleus by a multivariate statistical analysis, aiming to distinguish homogeneous groups and to constrain the bulk composition. Methods. We applied the G-mode clustering algorithm to 16 OSIRIS data cubes acquired on 5 6 August 2014 (mostly covering the northern hemisphere) and 2 May 2015 (mostly covering the southern hemisphere), selected to have complete coverage of the comet's surface with similar observing conditions. Results. We found four similar homogeneous groups for each of the analysed cubes. The first group corresponds to the average spectrophotometric behaviour of the nucleus. The second (spectrally redder) and the third (spectrally bluer) groups are found in regions that were already found to deviate from the average terrain of the comet by previous studies. A fourth group (characterised by enhancements of the flux at 700 750 nm and 989 nm, possibly due to H2O+ and /or NH2 emissions) seems connected with the cometary activity rather than with the bulk composition. Conclusions. While our aim in this work was to study the spectrophotometric behaviour of the nucleus of 67P/Churyumov-Gerasimenko as a whole, we found that a follow-up application of the G-mode to smaller regions of the surface could be useful in particular to identify and study the temporal evolution of ice patches, as well as to constrain the composition and physical processes behind the emission of dust jets.
Published: 2017
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11. Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

Author: Lucchetti, A., Cremonese, G., Jorda, L., Poulet, F., Bibring, J. -P, Pajola, M., La Forgia, F., Massironi, M., El-Maarry, M. R., Oklay, N., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Preusker, F., Scholten, F., Thomas, N., Tubiana, C., Vincent, J. -B, Lucchetti, A., Cremonese, G., Jorda, L., Poulet, F., Bibring, J. -P, Pajola, M., La Forgia, F., Massironi, M., El-Maarry, M. R., Oklay, N., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Preusker, F., Scholten, F., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: Context. On 12 November 2014, the European mission Rosetta delivered the Philae lander on the nucleus of comet 67P /Churyumov-Gerasimenko (67P). After the first touchdown, the lander bounced three times before finally landing at a site named Abydos. Aims. We provide a morphologically detailed analysis of the Abydos landing site to support Philae's measurements and to give context for the interpretation of the images coming from the Comet Infrared and Visible Analyser (CIVA) camera system onboard the lander. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 6 December 2014 to perform the analysis of the Abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. We also computed the albedo and spectral reddening maps. Results. The morphological analysis of the region could suggest that Philae is located on a primordial terrain. The Abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km(2) talus deposit rich in boulders. The boulder size frequency distribution gives a cumulative power-law index of 4.0 + 0.3/0.4, which is correlated with gravitational events triggered by sublimation and /or thermal fracturing causing regressive erosion. The average value of the albedo is 5.8% at lambda(1) = 480.7 nm and 7.4% at lambda(2) = 649.2 nm, which is similar to the global albedos derived by OSIRIS and CIVA, respectively.
Published: 2016
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12. Variegation of comet 67P/Churyumov-Gerasimenko in regions showing activity

Author: Oklay, N., Vincent, J. -B, Fornasier, S., Pajola, M., Besse, S., Davidsson, Björn J. R., Lara, L. M., Mottola, S., Naletto, G., Sierks, H., Barucci, A. M., Scholten, F., Preusker, F., Pommerol, A., Masoumzadeh, N., Lazzarin, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H., Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kuehrt, E., Kueppers, M., Lin, Z. -Y., Lopez Moreno, J. J., Marzari, F., Moreno, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Oklay, N., Vincent, J. -B, Fornasier, S., Pajola, M., Besse, S., Davidsson, Björn J. R., Lara, L. M., Mottola, S., Naletto, G., Sierks, H., Barucci, A. M., Scholten, F., Preusker, F., Pommerol, A., Masoumzadeh, N., Lazzarin, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H., Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R., Kuehrt, E., Kueppers, M., Lin, Z. -Y., Lopez Moreno, J. J., Marzari, F., Moreno, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Aims. We carried out an investigation of the surface variegation of comet 67P/Churyumov-Gerasimenko, the detection of regions showing activity, the determination of active and inactive surface regions of the comet with spectral methods, and the detection of fallback material. Methods. We analyzed multispectral data generated with Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) narrow angle camera (NAC) observations via spectral techniques, reflectance ratios, and spectral slopes in order to study active regions. We applied clustering analysis to the results of the reflectance ratios, and introduced the new technique of activity thresholds to detect areas potentially enriched in volatiles. Results. Local color inhomogeneities are detected over the investigated surface regions. Active regions, such as Hapi, the active pits of Seth and Ma'at, the clustered and isolated bright features in Imhotep, the alcoves in Seth and Ma'at, and the large alcove in Anuket, have bluer spectra than the overall surface. The spectra generated with OSIRIS NAC observations are dominated by cometary emissions of around 700 nm to 750 nm as a result of the coma between the comet's surface and the camera. One of the two isolated bright features in the Imhotep region displays an absorption band of around 700 nm, which probably indicates the existence of hydrated silicates. An absorption band with a center between 800-900 nm is tentatively observed in some regions of the nucleus surface. This absorption band can be explained by the crystal field absorption of Fe2+, which is a common spectral feature seen in silicates.
Published: 2016
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13. Sunset jets observed on comet 67P/Churyumov-Gerasimenko sustained by subsurface thermal lag

Author: Shi, X., Hu, X., Sierks, H., Guettler, C., A'Hearn, M., Blum, J., El-Maarry, M. R., Kuehrt, E., Mottola, S., Pajola, M., Oklay, N., Fornasier, S., Tubiana, C., Keller, H. U., Vincent, J. -B, Bodewits, D., Hoefner, S., Lin, Z. -Y, Gicquel, A., Hofmann, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fulle, M., Groussin, O., Gutierrez, P. J., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kueppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Thomas, N., Shi, X., Hu, X., Sierks, H., Guettler, C., A'Hearn, M., Blum, J., El-Maarry, M. R., Kuehrt, E., Mottola, S., Pajola, M., Oklay, N., Fornasier, S., Tubiana, C., Keller, H. U., Vincent, J. -B, Bodewits, D., Hoefner, S., Lin, Z. -Y, Gicquel, A., Hofmann, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fulle, M., Groussin, O., Gutierrez, P. J., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kueppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., and Thomas, N.
Abstract: We present observations of sunset jets on comet 67P/Churyumov-Gerasimenko by Rosetta/OSIRIS camera. In late April 2015, when the comet was at a heliocentric distance of similar to 1.8AU, clusters of dust jets that originated in the Ma'at region on the comet's small lobe were identified from multiple images and were apparently sustained for about an hour beyond local sunset. Emanating from the shadowed nucleus, these jets became visible by solar illumination at their apparent sources up to only a few tens of meters above the nucleus surface. We investigate the plausibility of these jets as having been triggered by water ice sublimation and sustained by thermal lag in the subsurface beyond sunset. A general thermo-physical model was parameterized such that the thermal lag in the subsurface is consistent with the elapsed time of observation after sunset. It is found that the sublimation of water ice from a depth of 6 mm and with a low thermal inertia of 50 W m(-2) K-1 s(1/2) could explain the spatial pattern and evolution of the apparent sources, particularly their disappearance due to the eventual cooling of the subsurface. Our analysis suggests that these sunset jets were essentially day-side dust activities that continued after sunset. Specific observational conditions for the sunset jets constrain their possible sources to mostly within the less abrupt, dusty terrains. The uneven distribution of these jets is possibly related to subsurface inhomogeneities in the dusty area.
Published: 2016
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14. Are fractured cliffs the source of cometary dust jets? : Insights from OSIRIS/Rosetta at 67P/Churyumov-Gerasimenko

Author: Vincent, J. -B, Oklay, N., Pajola, M., Hoefner, S., Sierks, H., Hu, X., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W-H, Jordan, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Lowry, S., Marzari, F., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, Oklay, N., Pajola, M., Hoefner, S., Sierks, H., Hu, X., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W-H, Jordan, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Lowry, S., Marzari, F., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Context: Dust jets (i.e., fuzzy collimated streams of cometary material arising from the nucleus) have been observed in situ on all comets since the Giotto mission flew by comet 1P/Halley in 1986, and yet their formation mechanism remains unknown. Several solutions have been proposed involving either specific properties of the active areas or the local topography to create and focus the gas and dust flows. While the nucleus morphology seems to be responsible for the larger features, high resolution imagery has shown that broad streams are composed of many smaller jets (a few meters wide) that connect directly to the nucleus surface. Aims: We monitored these jets at high resolution and over several months to understand what the physical processes are that drive their formation and how this affects the surface. Methods: Using many images of the same areas with different viewing angles, we performed a 3-dimensional reconstruction of collimated jets and linked them precisely to their sources on the nucleus. Results: We show here observational evidence that the northern hemisphere jets of comet 67P/Churyumov-Gerasimenko arise from areas with sharp topographic changes and describe the physical processes involved. We propose a model in which active cliffs are the main source of jet-like features and therefore of the regions eroding the fastest on comets. We suggest that this is a common mechanism taking place on all comets.
Published: 2016
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15. The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 AU heliocentric distance range inbound

Author: Moreno, F., Snodgrass, C., Hainaut, O., Tubiana, C., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J-L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Ferri, F., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marques, P., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Thomas, N., Vincent, J. B., Della Corte, V., Fitzsimmons, A., Faggi, S., Jehin, E., Opitom, C., Tozzi, G-P, Moreno, F., Snodgrass, C., Hainaut, O., Tubiana, C., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J-L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Ferri, F., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marques, P., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Thomas, N., Vincent, J. B., Della Corte, V., Fitzsimmons, A., Faggi, S., Jehin, E., Opitom, C., and Tozzi, G-P
Abstract: Context: The ESA Rosetta spacecraft, currently orbiting around cornet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. Aims: To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. Methods: A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from. Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. Results: The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is alpha = -3, instead of alpha = -2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.
Published: 2016
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16. Possible interpretation of the precession of comet 67P/Churyumov-Gerasimenko

Author: Gutierrez, P. J., Jorda, L., Gaskell, R. W., Davidsson, Björn J. R., Capanna, C., Hviid, S. F., Keller, H. U., Maquet, L., Mottola, S., Preusker, F., Scholten, F., Lara, L. M., Moreno, F., Rodrigo, R., Sierks, H., Barbieri, C., Lamy, P., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Auger, A. T., Barucci, M. A., Bertaux, J. L., Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez-Marques, P., Guettler, C., Ip, W. H., Knollenberg, J., Kramm, J. R., Kueht, E., Kuppers, M., La Forgia, F., Lazzarin, M., Lopez-Moreno, J. J., Magrin, S., Marchi, S., Marzari, F., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Sabau, D., Thomas, N., Toth, I., Tubiana, C., Vincent, J. B., Gutierrez, P. J., Jorda, L., Gaskell, R. W., Davidsson, Björn J. R., Capanna, C., Hviid, S. F., Keller, H. U., Maquet, L., Mottola, S., Preusker, F., Scholten, F., Lara, L. M., Moreno, F., Rodrigo, R., Sierks, H., Barbieri, C., Lamy, P., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Auger, A. T., Barucci, M. A., Bertaux, J. L., Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez-Marques, P., Guettler, C., Ip, W. H., Knollenberg, J., Kramm, J. R., Kueht, E., Kuppers, M., La Forgia, F., Lazzarin, M., Lopez-Moreno, J. J., Magrin, S., Marchi, S., Marzari, F., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Sabau, D., Thomas, N., Toth, I., Tubiana, C., and Vincent, J. B.
Abstract: Context. Data derived from the reconstruction of the nucleus shape of comet 67P/Churyumov-Gerasimenko (67P) from images of the OSIRIS camera onboard ROSETTA show evidence that the nucleus rotates in complex mode. First, the orientation of the spin axis is not fixed in an inertial reference frame, which suggests a precessing motion around the angular momentum vector with a periodicity of approximately 257 h +/- 12 h. Second, periodograms of the right ascension and declination (RA/Dec) coordinates of the body-frame Z axis show a very significant (higher than 99.99%) periodicity at 276 h +/- 12 h, different from the rotational period of 12.40 h as previously determined from light-curve analysis. Aims. The main goal is to interpret the data and associated periodicities of the spin axis orientation in space. Methods. We analyzed the spin axis orientation in space and associated periodicities and compared them with solutions of Euler equations under the assumption that the body rotates in torque-free conditions. Statistical tests comparing the observationally derived spin axis orientation with the outcome from simulations were applied to determine the most likely inertia moments, excitation level, and periods. Results. Under the assumption that the body is solid-rigid and rotates in torque-free conditions, the most likely interpretation is that 67P is spinning around the principal axis with the highest inertia moment with a period of about 13 h. At the same time, the comet precesses around the angular momentum vector with a period of about 6.35 h. While the rotating period of such a body would be about 12.4 h, RA/Dec coordinates of the spin axis would have a periodicity of about 270 h as a result of the combination of the two aforementioned motions. Conclusions. The most direct and simple interpretation of the complex rotation of 67P requires a ratio of inertia moments significantly higher than that of a homogeneous body.
Published: 2016
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17. Evolution Of The Dust Size Distribution Of Comet 67P/Churyumov-Gerasimenko From 2.2 Au To Perihelion

Author: Fulle, M., Marzari, F., Della Corte, V., Fornasier, S., Sierks, H., Rotundi, A., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Lopez-Moreno, J. J., Accolla, M., Agarwal, J., A'Hearn, M. F., Altobelli, N., Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Bussoletti, E., Colangeli, L., Cosi, M., Cremonese, G., Crifo, J. -F, Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Esposito, F., Ferrari, M., Giovane, F., Gustafson, B., Green, S. F., Groussin, O., Gruen, E., Gutierrez, P., Guettler, C., Herranz, M. L., Hviid, S. F., Ip, W., Ivanovski, S. L., Jeronimo, J. M., Jorda, L., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Leese, M. R., Lopez-Jimenez, A. C., Lucarelli, F., Epifani, E. Mazzotta, McDonnell, J. A. M., Mennella, V., Molina, A., Morales, R., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Ortiz, J. L., Palomba, E., Palumbo, P., Perrin, J. -M, Rietmeijer, F. J. M., Rodriguez, J., Sordini, R., Thomas, N., Tubiana, C., Vincent, J. -B, Weissman, P., Wenzel, K. -P, Zakharov, V., Zarnecki, J. C., Fulle, M., Marzari, F., Della Corte, V., Fornasier, S., Sierks, H., Rotundi, A., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Lopez-Moreno, J. J., Accolla, M., Agarwal, J., A'Hearn, M. F., Altobelli, N., Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Bussoletti, E., Colangeli, L., Cosi, M., Cremonese, G., Crifo, J. -F, Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Esposito, F., Ferrari, M., Giovane, F., Gustafson, B., Green, S. F., Groussin, O., Gruen, E., Gutierrez, P., Guettler, C., Herranz, M. L., Hviid, S. F., Ip, W., Ivanovski, S. L., Jeronimo, J. M., Jorda, L., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Leese, M. R., Lopez-Jimenez, A. C., Lucarelli, F., Epifani, E. Mazzotta, McDonnell, J. A. M., Mennella, V., Molina, A., Morales, R., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Ortiz, J. L., Palomba, E., Palumbo, P., Perrin, J. -M, Rietmeijer, F. J. M., Rodriguez, J., Sordini, R., Thomas, N., Tubiana, C., Vincent, J. -B, Weissman, P., Wenzel, K. -P, Zakharov, V., and Zarnecki, J. C.
Abstract: The Rosetta probe, orbiting Jupiter-family comet 67P/Churyumov-Gerasimenko, has been detecting individual dust particles of mass larger than 10(-10) kg by means of the GIADA dust collector and the OSIRIS Wide Angle Camera and Narrow Angle Camera since 2014 August and will continue until 2016 September. Detections of single dust particles allow us to estimate the anisotropic dust flux from 67P, infer the dust loss rate and size distribution at the surface of the sunlit nucleus, and see whether the dust size distribution of 67P evolves in time. The velocity of the Rosetta orbiter, relative to 67P, is much lower than the dust velocity measured by GIADA, thus dust counts when GIADA is nadir-pointing will directly provide the dust flux. In OSIRIS observations, the dust flux is derived from the measurement of the dust space density close to the spacecraft. Under the assumption of radial expansion of the dust, observations in the nadir direction provide the distance of the particles by measuring their trail length, with a parallax baseline determined by the motion of the spacecraft. The dust size distribution at sizes > 1 mm observed by OSIRIS is consistent with a differential power index of -4, which was derived from models of 67P's trail. At sizes <1 mm, the size distribution observed by GIADA shows a strong time evolution, with a differential power index drifting from -2 beyond 2 au to -3.7 at perihelion, in agreement with the evolution derived from coma and tail models based on ground-based data. The refractory-to-water mass ratio of the nucleus is close to six during the entire inbound orbit and at perihelion.
Published: 2016
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18. Physical properties and dynamical relation of the circular depressions on comet 67P/Churyumov-Gerasimenko

Author: Ip, W. -H, Lai, I. -L, Lee, J. -C, Cheng, Y. -C, Li, Y., Lin, Z. -Y, Vincent, J. -B, Besse, S., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., La Forgia, F., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Lowry, S., Marchi, S., Marzari, F., Michalik, H., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Thomas, N., Toth, E., Tubiana, C., Ip, W. -H, Lai, I. -L, Lee, J. -C, Cheng, Y. -C, Li, Y., Lin, Z. -Y, Vincent, J. -B, Besse, S., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., La Forgia, F., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Lowry, S., Marchi, S., Marzari, F., Michalik, H., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Thomas, N., Toth, E., and Tubiana, C.
Abstract: Aims. We aim to characterize the circular depressions of comet 67P/Churyumov-Gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a Jupiter family comet (JFC). Methods. The images from the Rosetta/OSIRIS science camera experiment are used to construct size frequency distributions of the circular depression structures on comet 67P and they are compared with those of the JFCs 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2. The orbital evolutionary histories of these comets over the past 100 000 yr are analyzed statistically and compared with each other. Results. The global distribution of the circular depressions over the surface of 67P is charted and classified. Descriptions are given to the characteristics and cumulative size frequency distribution of the identified features. Orbital statistics of the JFCs visited by spacecraft are derived. Conclusions. The size frequency distribution of the circular depressions is found to have a similar power law distribution to those of 9P/Tempel 1 and 81P/Wild 2. This might imply that they could have been generated by the same process. Orbital integration calculation shows that the surface erosion histories of 81P/Wild 2, and 9P/Tempel 1 could be shorter than those of 67P, 103 P/Hartley 2 and 19P/Borrelly. From this point of view, the circular depressions could be dated back to the pre-JFC phase or the transneptunian phase of these comets. The north-south asymmetry in the distribution of the circular depressions could be associated with the heterogeneous structure of the nucleus of comet 67P and/or the solar insolation history.
Published: 2016
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19. Detection of exposed H2O ice on the nucleus of comet 67P/Churyumov-Gerasimenko as observed by Rosetta OSIRIS and VIRTIS instruments

Author: Barucci, M. A., Filacchione, G., Fornasier, S., Raponi, A., Deshapriya, J. D. P., Tosi, F., Feller, C., Ciarniello, M., Sierks, H., Capaccioni, F., Pommerol, A., Massironi, M., Oklay, N., Merlin, F., Vincent, J. -B, Fulchignoni, M., Guilbert-Lepoutre, A., Perna, D., Capria, M. T., Hasselmann, P. H., Rousseau, B., Barbieri, C., Bockelee-Morvan, D., Lamy, P. L., De Sanctis, C., Rodrigo, R., Erard, S., Koschny, D., Leyrat, C., Rickman, Hans, Drossart, P., Keller, H. U., A'Hearn, M. F., Arnold, G., Bertaux, J. -L, Bertini, I., Cerroni, P., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., El-Maarry, M. R., Fonti, S., Fulle, M., Groussin, O., Guettler, C., Hviid, S. F., Ip, W., Jorda, L., Kappel, D., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L., Lazzarin, M., Moreno, J. J. Lopez, Mancarella, F., Marzari, F., Mottola, S., Naletto, G., Pajola, M., Palomba, E., Quirico, E., Schmitt, B., Thomas, N., Tubiana, C., Barucci, M. A., Filacchione, G., Fornasier, S., Raponi, A., Deshapriya, J. D. P., Tosi, F., Feller, C., Ciarniello, M., Sierks, H., Capaccioni, F., Pommerol, A., Massironi, M., Oklay, N., Merlin, F., Vincent, J. -B, Fulchignoni, M., Guilbert-Lepoutre, A., Perna, D., Capria, M. T., Hasselmann, P. H., Rousseau, B., Barbieri, C., Bockelee-Morvan, D., Lamy, P. L., De Sanctis, C., Rodrigo, R., Erard, S., Koschny, D., Leyrat, C., Rickman, Hans, Drossart, P., Keller, H. U., A'Hearn, M. F., Arnold, G., Bertaux, J. -L, Bertini, I., Cerroni, P., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., El-Maarry, M. R., Fonti, S., Fulle, M., Groussin, O., Guettler, C., Hviid, S. F., Ip, W., Jorda, L., Kappel, D., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L., Lazzarin, M., Moreno, J. J. Lopez, Mancarella, F., Marzari, F., Mottola, S., Naletto, G., Pajola, M., Palomba, E., Quirico, E., Schmitt, B., Thomas, N., and Tubiana, C.
Abstract: Context. Since the orbital insertion of the Rosetta spacecraft, comet 67P/Churyumov-Gerasimenko (67P) has been mapped by OSIRIS camera and VIRTIS spectro-imager, producing a huge quantity of images and spectra of the comet's nucleus. Aims. The aim of this work is to search for the presence of H2O on the nucleus which, in general, appears very dark and rich in dehydrated organic material. After selecting images of the bright spots which could be good candidates to search for H2O ice, taken at high resolution by OSIRIS, we check for spectral cubes of the selected coordinates to identify these spots observed by VIRTIS. Methods. The selected OSIRIS images were processed with the OSIRIS standard pipeline and corrected for the illumination conditions for each pixel using the Lommel-Seeliger disk law. The spots with higher I/F were selected and then analysed spectrophotometrically and compared with the surrounding area. We selected 13 spots as good targets to be analysed by VIRTIS to search for the 2 mu m absorption band of water ice in the VIRTIS spectral cubes. Results. Out of the 13 selected bright spots, eight of them present positive H2O ice detection on the VIRTIS data. A spectral analysis was performed and the approximate temperature of each spot was computed. The H2O ice content was confirmed by modeling the spectra with mixing (areal and intimate) of H2O ice and dark terrain, using Hapke's radiative transfer modeling. We also present a detailed analysis of the detected spots.
Published: 2016
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20. Observations and analysis of a curved jet in the coma of comet 67P/Churyumov-Gerasimenko

Author: Lin, Z. -Y, Lai, I. -L, Su, C. -C, Ip, W. -H, Lees, J. -C, Wu, J. -S, Vincent, J. -B, La Forgia, F., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Lowry, S., Marzari, F., Michalik, H., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Rozek, A., Thomas, N., Tubiana, C., Lin, Z. -Y, Lai, I. -L, Su, C. -C, Ip, W. -H, Lees, J. -C, Wu, J. -S, Vincent, J. -B, La Forgia, F., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Lowry, S., Marzari, F., Michalik, H., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Rozek, A., Thomas, N., and Tubiana, C.
Abstract: Aims. We analyze the physical properties and dynamical origin of a curved jet of comet 67P/Churyumov-Gerasimenko that was observed repeatedly in several nucleus rotations starting on May 30 and persisting until early August, 2015. Methods. We simulated the motion of dust grains ejected from the nucleus surface under the influence of the gravity and viscous drag e ff ect of the expanding gas flow from the rotating nucleus. Results. The formation of the curved jet is a combination of the size of the dust particles (similar to 0.1-1 mm) and the location of the source region near the nucleus equator. This enhances the spiral feature of the collimated dust stream after the dust is accelerated to a terminal speed on the order of m s(-1).
Published: 2016
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21. Regional surface morphology of comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images : The southern hemisphere

Author: El-Marry, M. R., Thomas, N., Gracia-Berna, A., Pajola, M., Lee, J. -C, Massironi, M., Davidsson, B., Marchi, S., Keller, H. U., Hviid, S. F., Besse, S., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Gremonese, G., Da Deppo, V., De Cecco, M., Dehei, S., Guettler, C., Fornasier, S., Fulle, M., Giacomini, L., Groussin, O., Gutierrez, P. J., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marschall, R., Marzari, F., Naletto, G., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., Vincent, J. -B, El-Marry, M. R., Thomas, N., Gracia-Berna, A., Pajola, M., Lee, J. -C, Massironi, M., Davidsson, B., Marchi, S., Keller, H. U., Hviid, S. F., Besse, S., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Bertini, I., Bodewits, D., Gremonese, G., Da Deppo, V., De Cecco, M., Dehei, S., Guettler, C., Fornasier, S., Fulle, M., Giacomini, L., Groussin, O., Gutierrez, P. J., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marschall, R., Marzari, F., Naletto, G., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., and Vincent, J. -B
Abstract: Aims. The OSIRIS camera on board the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P)'s nucleus since August 2014. Starting in May 2015, the southern hemisphere gradually became illuminated and was imaged for the first time. Here we present the regional morphology of the southern hemisphere, which serves as a companion to an earlier paper that presented the regional morphology of the northern hemisphere. Methods. We used OSIRIS images that were acquired at orbits similar to 45-125 km from the center of the comet (corresponding to spatial resolutions of similar to 0.8 to 2.3 m/pixel) coupled with the use of digital terrain models to define the different regions on the surface, and identify structural boundaries accurately. Results. Seven regions have been defined in the southern hemisphere bringing the total number of defined regions on the surface of the nucleus to 26. These classifications are mainly based on morphological and/or topographic boundaries. The southern hemisphere shows a remarkable dichotomy with its northern counterpart mainly because of the absence of wide-scale smooth terrains, dust coatings and large unambiguous depressions. As a result, the southern hemisphere closely resembles previously identified consolidated regions. An assessment of the overall morphology of comet 67P suggests that the comet's two lobes show surface heterogeneities manifested in different physical/mechanical characteristics, possibly extending to local (i.e., within a single region) scales., Carroection in Astronomy and Astrophysics, Volume 596, article number C2. DOI: 10.1051/0004-6361/201628634e
Published: 2016
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22. Changes in the physical environment of the inner coma of 67p/churyumov-gerasimenko with decreasing heliocentric distance

Author: Bodewits, D., Lara, L. M., A'Hearn, M. F., La Forgia, F., Gicquel, A., Kovacs, G., Knollenberg, J., Lazzarin, M., Lin, Z. -Y, Shi, X., Snodgrass, C., Tubiana, C., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Thomas, N., Toth, I., Vincent, J. -B, Bodewits, D., Lara, L. M., A'Hearn, M. F., La Forgia, F., Gicquel, A., Kovacs, G., Knollenberg, J., Lazzarin, M., Lin, Z. -Y, Shi, X., Snodgrass, C., Tubiana, C., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Thomas, N., Toth, I., and Vincent, J. -B
Abstract: The Wide Angle Camera of the OSIRIS instrument on board the Rosetta spacecraft is equipped with several narrow-band filters that are centered on the emission lines and bands of various fragment species. These are used to determine the evolution of the production and spatial distribution of the gas in the inner coma of comet 67P with time and heliocentric distance, here between 2.6 and 1.3 au pre-perihelion. Our observations indicate that the emission observed in the OH, OI, CN, NH, and NH2 filters is mostly produced by dissociative electron impact excitation of different parent species. We conclude that CO2 rather than H2O is a significant source of the [OI] 630 nm emission. A strong plume-like feature observed in the CN and OI filters is present throughout our observations. This plume is not present in OH emission and indicates a local enhancement of the CO2/H2O ratio by as much as a factor of 3. We observed a sudden decrease in intensity levels after 2015 March, which we attribute to decreased electron temperatures in the first few kilometers above the surface of the nucleus.
Published: 2016
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23. Summer fireworks on comet 67P

Author: Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: During its 2 yr mission around comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft had the unique opportunity to follow closely a comet in the most active part of its orbit. Many studies have presented the typical features associated with the activity of the nucleus, such as localized dust and gas jets. Here, we report on series of more energetic transient events observed during the 3 months surrounding the comet's perihelion passage in 2015 August. We detected and characterized 34 outbursts with the Rosetta cameras, one every 2.4 nucleus rotations. We identified three main dust plume morphologies associated with these events: a narrow jet, a broad fan, and more complex plumes featuring both previous types together. These plumes are comparable in scale and temporal variation to what has been observed on other comets. We present a map of the outbursts' source locations, and discuss the associated topography. We find that the spatial distribution sources on the nucleus correlate well with morphological region boundaries, especially in areas marked by steep scarps or cliffs. Outbursts occur either in the early morning or shortly after the local noon, indicating two potential processes: morning outbursts may be triggered by thermal stresses linked to the rapid change of temperature; afternoon events are most likely related to the diurnal or seasonal heat wave reaching volatiles buried under the first surface layer. In addition, we propose that some events can be the result of a completely different mechanism, in which most of the dust is released upon the collapse of a cliff.
Published: 2016
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24. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras on board Rosetta

Author: Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance R-h = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this paper was that through the sublimation of the aggregates of dirty grains (radius a between 5 and 50 mu m) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data, we needed to inject a number of aggregates between 8.5 x 10(13) and 8.5 x 10(10) for a = 5 and 50 mu m, respectively, or an initial mass of H2O ice around 22 kg.
Published: 2016
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25. The 2016 Feb 19 outburst of comet 67P/CG : an ESA Rosetta multi-instrument study

Author: Grun, E., Agarwal, J., Altobelli, N., Altwegg, K., Bentley, M. S., Biver, N., Della Corte, V., Edberg, Niklas J. T., Feldman, P. D., Galand, M., Geiger, B., Goetz, C., Grieger, B., Guettler, C., Henri, P., Hofstadter, M., Horanyi, M., Jehin, E., Krueger, H., Lee, S., Mannel, T., Morales, E., Mousis, O., Mueller, M., Opitom, C., Rotundi, A., Schmied, R., Schmidt, F., Sierks, H., Snodgrass, C., Soja, R. H., Sommer, M., Srama, R., Tzou, C. -Y, Vincent, J. -B, Yanamandra-Fisher, P., A'Hearn, M. F., Eriksson, Anders, Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Burch, J., Colangeli, L., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Feaga, L. M., Ferrari, M., Fornasier, S., Fulle, M., Gicquel, A., Gillon, M., Green, S. F., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Ivanovski, S., Jorda, L., Keller, H. U., Knight, M. M., Knollenberg, J., Koschny, D., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lamy, P. L., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Manfroid, J., Epifani, E. Mazzotta, Marzari, F., Naletto, G., Oklay, N., Palumbo, P., Parker, J. Wm., Rickman, Hans, Rodrigo, R., Rodriguez, J., Schindhelm, E., Shi, X., Sordini, R., Steffl, A. J., Stern, S. A., Thomas, N., Tubiana, C., Weaver, H. A., Weissman, P., Zakharov, V. V., Grun, E., Agarwal, J., Altobelli, N., Altwegg, K., Bentley, M. S., Biver, N., Della Corte, V., Edberg, Niklas J. T., Feldman, P. D., Galand, M., Geiger, B., Goetz, C., Grieger, B., Guettler, C., Henri, P., Hofstadter, M., Horanyi, M., Jehin, E., Krueger, H., Lee, S., Mannel, T., Morales, E., Mousis, O., Mueller, M., Opitom, C., Rotundi, A., Schmied, R., Schmidt, F., Sierks, H., Snodgrass, C., Soja, R. H., Sommer, M., Srama, R., Tzou, C. -Y, Vincent, J. -B, Yanamandra-Fisher, P., A'Hearn, M. F., Eriksson, Anders, Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Burch, J., Colangeli, L., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Feaga, L. M., Ferrari, M., Fornasier, S., Fulle, M., Gicquel, A., Gillon, M., Green, S. F., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Ivanovski, S., Jorda, L., Keller, H. U., Knight, M. M., Knollenberg, J., Koschny, D., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lamy, P. L., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Manfroid, J., Epifani, E. Mazzotta, Marzari, F., Naletto, G., Oklay, N., Palumbo, P., Parker, J. Wm., Rickman, Hans, Rodrigo, R., Rodriguez, J., Schindhelm, E., Shi, X., Sordini, R., Steffl, A. J., Stern, S. A., Thomas, N., Tubiana, C., Weaver, H. A., Weissman, P., and Zakharov, V. V.
Abstract: On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09: 40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors > 100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors > 10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from similar to-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta ( 34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (similar to 25 m s(-1)) while 100 mu m radius particles were detected by the GIADA dust instrument similar to 1 h later at a speed of 6 m s(-1). The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
Published: 2016
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26. Comparative study of water ice exposures on cometary nuclei using multispectral imaging data

Author: Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., Tubiana, C., Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., and Tubiana, C.
Abstract: Deep Impact, EPOXI and Rosetta missions visited comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko, respectively. Each of these three missions was equipped with both multispectral imagers and infrared spectrometers. Bright blue features containing water ice were detected in each of these comet nuclei. We analysed multispectral properties of enriched water ice features observed via Optical, Spectroscopic, and Infrared Remote Imaging System narrow angle camera on comet 67P in the wavelength range of 260-1000 nm and then compared with multispectral data of water ice deposits observed on comets 9P and 103P. We characterize the UV/VIS properties of water-ice-rich features observed on the nuclei of these three comets. When compared to the average surface of each comet, our analysis shows that the water ice deposits seen on comet 9P are similar to the clustered water-ice-rich features seen on comet 67P, while the water ice deposit seen on comet 103P is more akin to two large isolated water-ice-rich features seen on comet 67P. Our results indicate that the water ice deposit observed on comet 103P contains more water ice than the water-ice-rich features observed on comets 9P and 67P, proportionally to the average surface of each nucleus.
Published: 2016
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27. Geologic mapping of the Comet 67P/Churyumov-Gerasimenko's Northern hemisphere

Author: Giacomini, L., Massironi, M., El-Maarry, M. R., Penasa, L., Pajola, M., Thomas, N., Lowry, S. C., Barbieri, C., Cremonese, G., Ferri, F., Naletto, G., Bertini, I., La Forgia, F., Lazzarin, M., Marzari, F., Sierks, H., Lamy, P. L., Rodrigo, R., Rickman, Hans, Koschny, D., Keller, H. U., Agarwal, J., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Besse, S., Bodewits, D., Da Deppo, V., Davidsson, Björn, De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Magrin, S., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., Vincent, J. -B, Giacomini, L., Massironi, M., El-Maarry, M. R., Penasa, L., Pajola, M., Thomas, N., Lowry, S. C., Barbieri, C., Cremonese, G., Ferri, F., Naletto, G., Bertini, I., La Forgia, F., Lazzarin, M., Marzari, F., Sierks, H., Lamy, P. L., Rodrigo, R., Rickman, Hans, Koschny, D., Keller, H. U., Agarwal, J., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Besse, S., Bodewits, D., Da Deppo, V., Davidsson, Björn, De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Magrin, S., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., and Vincent, J. -B
Abstract: The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), the scientific imaging system onboard the Rosetta mission, has been acquiring images of the nucleus of the comet 67P/Churyumov-Gerasimenko since 2014 August with a resolution which allows a detailed analysis of its surface. Indeed, data reveal a complex surface morphology which is likely the expression of different processes which occurred at different times on the cometary nucleus. In order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67P Northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. For this purpose, we used narrow-angle camera images acquired in 2014 August and September with a spatial scale ranging from 1.2 to 2.4 m pixel(-1). Several different geologic units have been identified on the basis of their different surface textures, granulometry and morphology. Some of these units are distinctive and localized, whereas others are more common and distributed all over the Northern hemisphere. Moreover, different types of linear features have been distinguished on the basis of their morphology. Some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. The geologic mapping results presented here will allow us to better understand the processes which affected the nucleus' surface and thus the origin and evolutionary history of comet 67P/Churyumov-Gerasimenko.
Published: 2016
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28. Acceleration of individual, decimetre-sized aggregates in the lower coma of comet 67P/Churyumov-Gerasimenko

Author: Agarwal, Jessica, A'Hearn, M. F., Vincent, J. -B, Guettler, C., Hoefner, S., Sierks, H., Tubiana, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., Thomas, N., Agarwal, Jessica, A'Hearn, M. F., Vincent, J. -B, Guettler, C., Hoefner, S., Sierks, H., Tubiana, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., and Thomas, N.
Abstract: We present observations of decimetre-sized, likely ice-containing aggregates ejected from a confined region on the surface of comet 67P/Churyumov-Gerasimenko. The images were obtained with the narrow angle camera of the Optical, Spectroscopic, and Infrared Remote Imaging System on board the Rosetta spacecraft in 2016 January when the comet was at 2 au from the Sun outbound from perihelion. We measure the acceleration of individual aggregates through a 2 h image series. Approximately 50 per cent of the aggregates are accelerated away from the nucleus, and 50 per cent towards it, and likewise towards either horizontal direction. The accelerations are up to one order of magnitude stronger than local gravity, and are most simply explained by the combined effect of gas drag accelerating all aggregates upwards, and the recoil force from asymmetric outgassing, either from rotating aggregates with randomly oriented spin axes and sufficient thermal inertia to shift the temperature maximum away from an aggregate's subsolar region, or from aggregates with variable ice content. At least 10 per cent of the aggregates will escape the gravity field of the nucleus and feed the comet's debris trail, while others may fall back to the surface and contribute to the deposits covering parts of the Northern hemisphere. The rocket force plays a crucial role in pushing these aggregates back towards the surface. Our observations show the future back fall material in the process of ejection, and provide the first direct measurement of the acceleration of aggregates in the innermost coma (<2 km) of a comet, where gas drag is still significant.
Published: 2016
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29. Spectrophotometry of the Khonsu region on the comet 67P/Churyumov-Gerasimenko using OSIRIS instrument images

Author: Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Feller, C., Hasselmann, P. H., Sierks, H., El-Maarry, M. R., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Deller, J., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Perna, D., Pommerol, A., Thomas, N., Tubiana, C., Vincent, J. -B, Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Feller, C., Hasselmann, P. H., Sierks, H., El-Maarry, M. R., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Deller, J., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Perna, D., Pommerol, A., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: Our work focuses on the spectrophotometric analysis of selected terrain and bright patches in the Khonsu region on the comet 67P/Churyumov-Gerasimenko. Despite the variety of geological features, their spectrophotometric properties appear to indicate a similar composition. It is noticeable that the smooth areas in Khonsu possess similar spectrophotometric behaviour to some other regions of the comet. We observed bright patches on Khonsu with an estimation of >40 per cent of normal albedo and suggest that they are associated with H2O ice. One of the studied bright patches has been observed to exist on the surface for more than 5 months without a major decay of its size, implying the existence of potential sub-surface icy layers. Its location may be correlated with a cometary outburst during the perihelion passage of the comet in 2015 August, and we interpret it to have triggered the surface modifications necessary to unearth the stratified icy layers beneath the surface. A boulder analysis on Khonsu leads to a power-law index of -3.1 + 0.2/-0.3 suggesting a boulder formation, shaped by varying geological processes for different morphological units.
Published: 2016
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30. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

Author: Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Jost, B., Poch, O., ElMaary, M. R., Thomas, N., Belskaya, I., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H, Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Perna, D., Oklay, N., Shi, X., Tubiana, C., Vincent, J. -B, Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Jost, B., Poch, O., ElMaary, M. R., Thomas, N., Belskaya, I., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H, Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Perna, D., Oklay, N., Shi, X., Tubiana, C., and Vincent, J. -B
Abstract: We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov-Gerasimenko nucleus derived with the Optical, Spectroscopic and Infrared Remote Imaging System instrument during the closest fly-by over the comet, which took place on 2015 February 14 at a distance of similar to 6 km from the surface. Several images covering the 0 degrees-33 degrees. phase angle range were acquired, and the spatial resolution achieved was 11 cm pixel(-1). The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40 per cent between bright spots and sombre regions, and spectral slope variations up to 50 per cent. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our data set using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8 per cent) and it has a high porosity value in the uppermost layers (86 per cent). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.
Published: 2016
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31. The global shape, density and rotation of Comet 67P/Churyumov-Gerasimenko from preperihelion Rosetta/OSIRIS observations

Author: Jorda, L., Gaskell, R., Capanna, C., Hviid, S., Lamy, P., Durech, J., Faury, G., Groussin, O., Gutierrez, P., Jackman, C., Keihm, S. J., Keller, H. U., Knollenberg, J., Kuehrt, E., Marchi, S., Mottola, S., Palmer, E., Schloerb, F. P., Sierks, H., Vincent, J. -B, A'Hearn, M. F., Barbieri, C., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. L., Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Guettler, C., Ip, W. -H, Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Thomas, N., Tubiana, C., Wenzel, K-P, Jorda, L., Gaskell, R., Capanna, C., Hviid, S., Lamy, P., Durech, J., Faury, G., Groussin, O., Gutierrez, P., Jackman, C., Keihm, S. J., Keller, H. U., Knollenberg, J., Kuehrt, E., Marchi, S., Mottola, S., Palmer, E., Schloerb, F. P., Sierks, H., Vincent, J. -B, A'Hearn, M. F., Barbieri, C., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. L., Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Guettler, C., Ip, W. -H, Kramm, J. R., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Thomas, N., Tubiana, C., and Wenzel, K-P
Abstract: The Rosetta spacecraft reached Comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) in August 2014 at an heliocentric distance of 3.6 a.u. and was then put in orbit around its nucleus to perform detailed observations. Among the collected data are the images acquired by the OSIRIS instrument up to the perihelion passage of the comet in August 2015, which allowed us to map the entire nucleus surface at high-resolution in the visible. Stereophotoclinometry methods have been used to reconstruct a global high-resolution shape model and to monitor its rotational parameters using data collected up to perihelion. The nucleus has a conspicuous bilobate shape with overall dimensions along its principal axes of (4.34 +/- 0.02) x (2.60 +/- 0.02) x (2.12 +/- 0.06) km. The best-fit ellipsoid dimensions of the individual lobes along their principal axes of inertia are found to be 4.10 x 3.52 x 1.63 km and 2.50 x 2.14 x 1.641cm. Their volume amounts to 66% and 27% of the total volume of the nucleus. The two lobes are connected by a "neck" whose volume has been estimated to represent similar to 7% of the total volume of the comet. Combining the derived volume of 18.8 +/- 0.3 km(3) with the mass of 9.982 +/- 0.003 x 10(12) kg determined by the Rosetta/RSI experiment, we obtained a bulk density of the nucleus of 532 +/- 7 kg m(-3). Together with the companion value of 535 35 kg m-3 deduced from the stereophotogrammetry shape model of the nucleus (Preusker et al. [2015] Astron. Astrophys. 583, A33), these constitute the first reliable and most accurate determination of the density of a cometary nucleus to date. The calculated porosity is quite large, ranging approximately from 70% to 75% depending upon the assumed density of the dust grains and the dust-to-ice mass ratio. The nature of the porosity, either micro or macro or both, remains unconstrained. The coordinates of the center of gravity are not compatible with a uniform nucleus density. The direction of the offset between the cent
Published: 2016
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32. Summer fireworks on comet 67P

Author: Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: During its 2 yr mission around comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft had the unique opportunity to follow closely a comet in the most active part of its orbit. Many studies have presented the typical features associated with the activity of the nucleus, such as localized dust and gas jets. Here, we report on series of more energetic transient events observed during the 3 months surrounding the comet's perihelion passage in 2015 August. We detected and characterized 34 outbursts with the Rosetta cameras, one every 2.4 nucleus rotations. We identified three main dust plume morphologies associated with these events: a narrow jet, a broad fan, and more complex plumes featuring both previous types together. These plumes are comparable in scale and temporal variation to what has been observed on other comets. We present a map of the outbursts' source locations, and discuss the associated topography. We find that the spatial distribution sources on the nucleus correlate well with morphological region boundaries, especially in areas marked by steep scarps or cliffs. Outbursts occur either in the early morning or shortly after the local noon, indicating two potential processes: morning outbursts may be triggered by thermal stresses linked to the rapid change of temperature; afternoon events are most likely related to the diurnal or seasonal heat wave reaching volatiles buried under the first surface layer. In addition, we propose that some events can be the result of a completely different mechanism, in which most of the dust is released upon the collapse of a cliff.
Published: 2016
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33. Summer fireworks on comet 67P

Author: Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: During its 2 yr mission around comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft had the unique opportunity to follow closely a comet in the most active part of its orbit. Many studies have presented the typical features associated with the activity of the nucleus, such as localized dust and gas jets. Here, we report on series of more energetic transient events observed during the 3 months surrounding the comet's perihelion passage in 2015 August. We detected and characterized 34 outbursts with the Rosetta cameras, one every 2.4 nucleus rotations. We identified three main dust plume morphologies associated with these events: a narrow jet, a broad fan, and more complex plumes featuring both previous types together. These plumes are comparable in scale and temporal variation to what has been observed on other comets. We present a map of the outbursts' source locations, and discuss the associated topography. We find that the spatial distribution sources on the nucleus correlate well with morphological region boundaries, especially in areas marked by steep scarps or cliffs. Outbursts occur either in the early morning or shortly after the local noon, indicating two potential processes: morning outbursts may be triggered by thermal stresses linked to the rapid change of temperature; afternoon events are most likely related to the diurnal or seasonal heat wave reaching volatiles buried under the first surface layer. In addition, we propose that some events can be the result of a completely different mechanism, in which most of the dust is released upon the collapse of a cliff.
Published: 2016
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34. Comparative study of water ice exposures on cometary nuclei using multispectral imaging data

Author: Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., Tubiana, C., Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., and Tubiana, C.
Abstract: Deep Impact, EPOXI and Rosetta missions visited comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko, respectively. Each of these three missions was equipped with both multispectral imagers and infrared spectrometers. Bright blue features containing water ice were detected in each of these comet nuclei. We analysed multispectral properties of enriched water ice features observed via Optical, Spectroscopic, and Infrared Remote Imaging System narrow angle camera on comet 67P in the wavelength range of 260-1000 nm and then compared with multispectral data of water ice deposits observed on comets 9P and 103P. We characterize the UV/VIS properties of water-ice-rich features observed on the nuclei of these three comets. When compared to the average surface of each comet, our analysis shows that the water ice deposits seen on comet 9P are similar to the clustered water-ice-rich features seen on comet 67P, while the water ice deposit seen on comet 103P is more akin to two large isolated water-ice-rich features seen on comet 67P. Our results indicate that the water ice deposit observed on comet 103P contains more water ice than the water-ice-rich features observed on comets 9P and 67P, proportionally to the average surface of each nucleus.
Published: 2016
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35. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras on board Rosetta

Author: Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance R-h = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this paper was that through the sublimation of the aggregates of dirty grains (radius a between 5 and 50 mu m) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data, we needed to inject a number of aggregates between 8.5 x 10(13) and 8.5 x 10(10) for a = 5 and 50 mu m, respectively, or an initial mass of H2O ice around 22 kg.
Published: 2016
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36. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras on board Rosetta

Author: Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance R-h = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this paper was that through the sublimation of the aggregates of dirty grains (radius a between 5 and 50 mu m) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data, we needed to inject a number of aggregates between 8.5 x 10(13) and 8.5 x 10(10) for a = 5 and 50 mu m, respectively, or an initial mass of H2O ice around 22 kg.
Published: 2016
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37. The 2016 Feb 19 outburst of comet 67P/CG : an ESA Rosetta multi-instrument study

Author: Grun, E., Agarwal, J., Altobelli, N., Altwegg, K., Bentley, M. S., Biver, N., Della Corte, V., Edberg, Niklas J. T., Feldman, P. D., Galand, M., Geiger, B., Goetz, C., Grieger, B., Guettler, C., Henri, P., Hofstadter, M., Horanyi, M., Jehin, E., Krueger, H., Lee, S., Mannel, T., Morales, E., Mousis, O., Mueller, M., Opitom, C., Rotundi, A., Schmied, R., Schmidt, F., Sierks, H., Snodgrass, C., Soja, R. H., Sommer, M., Srama, R., Tzou, C. -Y, Vincent, J. -B, Yanamandra-Fisher, P., A'Hearn, M. F., Eriksson, Anders, Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Burch, J., Colangeli, L., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Feaga, L. M., Ferrari, M., Fornasier, S., Fulle, M., Gicquel, A., Gillon, M., Green, S. F., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Ivanovski, S., Jorda, L., Keller, H. U., Knight, M. M., Knollenberg, J., Koschny, D., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lamy, P. L., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Manfroid, J., Epifani, E. Mazzotta, Marzari, F., Naletto, G., Oklay, N., Palumbo, P., Parker, J. Wm., Rickman, Hans, Rodrigo, R., Rodriguez, J., Schindhelm, E., Shi, X., Sordini, R., Steffl, A. J., Stern, S. A., Thomas, N., Tubiana, C., Weaver, H. A., Weissman, P., Zakharov, V. V., Grun, E., Agarwal, J., Altobelli, N., Altwegg, K., Bentley, M. S., Biver, N., Della Corte, V., Edberg, Niklas J. T., Feldman, P. D., Galand, M., Geiger, B., Goetz, C., Grieger, B., Guettler, C., Henri, P., Hofstadter, M., Horanyi, M., Jehin, E., Krueger, H., Lee, S., Mannel, T., Morales, E., Mousis, O., Mueller, M., Opitom, C., Rotundi, A., Schmied, R., Schmidt, F., Sierks, H., Snodgrass, C., Soja, R. H., Sommer, M., Srama, R., Tzou, C. -Y, Vincent, J. -B, Yanamandra-Fisher, P., A'Hearn, M. F., Eriksson, Anders, Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Burch, J., Colangeli, L., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Feaga, L. M., Ferrari, M., Fornasier, S., Fulle, M., Gicquel, A., Gillon, M., Green, S. F., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Ivanovski, S., Jorda, L., Keller, H. U., Knight, M. M., Knollenberg, J., Koschny, D., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lamy, P. L., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Manfroid, J., Epifani, E. Mazzotta, Marzari, F., Naletto, G., Oklay, N., Palumbo, P., Parker, J. Wm., Rickman, Hans, Rodrigo, R., Rodriguez, J., Schindhelm, E., Shi, X., Sordini, R., Steffl, A. J., Stern, S. A., Thomas, N., Tubiana, C., Weaver, H. A., Weissman, P., and Zakharov, V. V.
Abstract: On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09: 40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors > 100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors > 10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from similar to-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta ( 34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (similar to 25 m s(-1)) while 100 mu m radius particles were detected by the GIADA dust instrument similar to 1 h later at a speed of 6 m s(-1). The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
Published: 2016
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38. The 2016 Feb 19 outburst of comet 67P/CG : an ESA Rosetta multi-instrument study

Author: Grun, E., Agarwal, J., Altobelli, N., Altwegg, K., Bentley, M. S., Biver, N., Della Corte, V., Edberg, Niklas J. T., Feldman, P. D., Galand, M., Geiger, B., Goetz, C., Grieger, B., Guettler, C., Henri, P., Hofstadter, M., Horanyi, M., Jehin, E., Krueger, H., Lee, S., Mannel, T., Morales, E., Mousis, O., Mueller, M., Opitom, C., Rotundi, A., Schmied, R., Schmidt, F., Sierks, H., Snodgrass, C., Soja, R. H., Sommer, M., Srama, R., Tzou, C. -Y, Vincent, J. -B, Yanamandra-Fisher, P., A'Hearn, M. F., Eriksson, Anders, Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Burch, J., Colangeli, L., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Feaga, L. M., Ferrari, M., Fornasier, S., Fulle, M., Gicquel, A., Gillon, M., Green, S. F., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Ivanovski, S., Jorda, L., Keller, H. U., Knight, M. M., Knollenberg, J., Koschny, D., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lamy, P. L., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Manfroid, J., Epifani, E. Mazzotta, Marzari, F., Naletto, G., Oklay, N., Palumbo, P., Parker, J. Wm., Rickman, Hans, Rodrigo, R., Rodriguez, J., Schindhelm, E., Shi, X., Sordini, R., Steffl, A. J., Stern, S. A., Thomas, N., Tubiana, C., Weaver, H. A., Weissman, P., Zakharov, V. V., Grun, E., Agarwal, J., Altobelli, N., Altwegg, K., Bentley, M. S., Biver, N., Della Corte, V., Edberg, Niklas J. T., Feldman, P. D., Galand, M., Geiger, B., Goetz, C., Grieger, B., Guettler, C., Henri, P., Hofstadter, M., Horanyi, M., Jehin, E., Krueger, H., Lee, S., Mannel, T., Morales, E., Mousis, O., Mueller, M., Opitom, C., Rotundi, A., Schmied, R., Schmidt, F., Sierks, H., Snodgrass, C., Soja, R. H., Sommer, M., Srama, R., Tzou, C. -Y, Vincent, J. -B, Yanamandra-Fisher, P., A'Hearn, M. F., Eriksson, Anders, Barbieri, C., Barucci, M. A., Bertaux, J. -L, Bertini, I., Burch, J., Colangeli, L., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Feaga, L. M., Ferrari, M., Fornasier, S., Fulle, M., Gicquel, A., Gillon, M., Green, S. F., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Ivanovski, S., Jorda, L., Keller, H. U., Knight, M. M., Knollenberg, J., Koschny, D., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lamy, P. L., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Manfroid, J., Epifani, E. Mazzotta, Marzari, F., Naletto, G., Oklay, N., Palumbo, P., Parker, J. Wm., Rickman, Hans, Rodrigo, R., Rodriguez, J., Schindhelm, E., Shi, X., Sordini, R., Steffl, A. J., Stern, S. A., Thomas, N., Tubiana, C., Weaver, H. A., Weissman, P., and Zakharov, V. V.
Abstract: On 2016 Feb 19, nine Rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras and spectrometers ranging from UV over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. At 09: 40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. The enhancement ranged from 50 per cent of the neutral gas density at Rosetta to factors > 100 of the brightness of the coma near the nucleus. Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors > 10). However, even the electron density at Rosetta increased by a factor 3 and consequently the spacecraft potential changed from similar to-16 V to -20 V during the outburst. A clear sequence of events was observed at the distance of Rosetta ( 34 km from the nucleus): within 15 min the Star Tracker camera detected fast particles (similar to 25 m s(-1)) while 100 mu m radius particles were detected by the GIADA dust instrument similar to 1 h later at a speed of 6 m s(-1). The slowest were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst originated just outside the FOV of the instruments, the source region and the magnitude of the outburst could be determined.
Published: 2016
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39. Comparative study of water ice exposures on cometary nuclei using multispectral imaging data

Author: Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., Tubiana, C., Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., and Tubiana, C.
Abstract: Deep Impact, EPOXI and Rosetta missions visited comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko, respectively. Each of these three missions was equipped with both multispectral imagers and infrared spectrometers. Bright blue features containing water ice were detected in each of these comet nuclei. We analysed multispectral properties of enriched water ice features observed via Optical, Spectroscopic, and Infrared Remote Imaging System narrow angle camera on comet 67P in the wavelength range of 260-1000 nm and then compared with multispectral data of water ice deposits observed on comets 9P and 103P. We characterize the UV/VIS properties of water-ice-rich features observed on the nuclei of these three comets. When compared to the average surface of each comet, our analysis shows that the water ice deposits seen on comet 9P are similar to the clustered water-ice-rich features seen on comet 67P, while the water ice deposit seen on comet 103P is more akin to two large isolated water-ice-rich features seen on comet 67P. Our results indicate that the water ice deposit observed on comet 103P contains more water ice than the water-ice-rich features observed on comets 9P and 67P, proportionally to the average surface of each nucleus.
Published: 2016
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40. Acceleration of individual, decimetre-sized aggregates in the lower coma of comet 67P/Churyumov-Gerasimenko

Author: Agarwal, Jessica, A'Hearn, M. F., Vincent, J. -B, Guettler, C., Hoefner, S., Sierks, H., Tubiana, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., Thomas, N., Agarwal, Jessica, A'Hearn, M. F., Vincent, J. -B, Guettler, C., Hoefner, S., Sierks, H., Tubiana, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., and Thomas, N.
Abstract: We present observations of decimetre-sized, likely ice-containing aggregates ejected from a confined region on the surface of comet 67P/Churyumov-Gerasimenko. The images were obtained with the narrow angle camera of the Optical, Spectroscopic, and Infrared Remote Imaging System on board the Rosetta spacecraft in 2016 January when the comet was at 2 au from the Sun outbound from perihelion. We measure the acceleration of individual aggregates through a 2 h image series. Approximately 50 per cent of the aggregates are accelerated away from the nucleus, and 50 per cent towards it, and likewise towards either horizontal direction. The accelerations are up to one order of magnitude stronger than local gravity, and are most simply explained by the combined effect of gas drag accelerating all aggregates upwards, and the recoil force from asymmetric outgassing, either from rotating aggregates with randomly oriented spin axes and sufficient thermal inertia to shift the temperature maximum away from an aggregate's subsolar region, or from aggregates with variable ice content. At least 10 per cent of the aggregates will escape the gravity field of the nucleus and feed the comet's debris trail, while others may fall back to the surface and contribute to the deposits covering parts of the Northern hemisphere. The rocket force plays a crucial role in pushing these aggregates back towards the surface. Our observations show the future back fall material in the process of ejection, and provide the first direct measurement of the acceleration of aggregates in the innermost coma (<2 km) of a comet, where gas drag is still significant.
Published: 2016
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41. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

Author: Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Jost, B., Poch, O., ElMaary, M. R., Thomas, N., Belskaya, I., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H, Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Perna, D., Oklay, N., Shi, X., Tubiana, C., Vincent, J. -B, Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Jost, B., Poch, O., ElMaary, M. R., Thomas, N., Belskaya, I., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H, Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Perna, D., Oklay, N., Shi, X., Tubiana, C., and Vincent, J. -B
Abstract: We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov-Gerasimenko nucleus derived with the Optical, Spectroscopic and Infrared Remote Imaging System instrument during the closest fly-by over the comet, which took place on 2015 February 14 at a distance of similar to 6 km from the surface. Several images covering the 0 degrees-33 degrees. phase angle range were acquired, and the spatial resolution achieved was 11 cm pixel(-1). The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40 per cent between bright spots and sombre regions, and spectral slope variations up to 50 per cent. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our data set using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8 per cent) and it has a high porosity value in the uppermost layers (86 per cent). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.
Published: 2016
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42. Decimetre-scaled spectrophotometric properties of the nucleus of comet 67P/Churyumov-Gerasimenko from OSIRIS observations

Author: Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Jost, B., Poch, O., ElMaary, M. R., Thomas, N., Belskaya, I., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H, Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Perna, D., Oklay, N., Shi, X., Tubiana, C., Vincent, J. -B, Feller, C., Fornasier, S., Hasselmann, P. H., Barucci, A., Preusker, F., Scholten, F., Jorda, L., Pommerol, A., Jost, B., Poch, O., ElMaary, M. R., Thomas, N., Belskaya, I., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Koschny, D., Rickman, Hans, Rodrigo, R., Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Giquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Keller, H., Ip, W. -H, Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Leyrat, C., Moreno, J. J. Lopez, Marzari, F., Masoumzadeh, N., Mottola, S., Naletto, G., Perna, D., Oklay, N., Shi, X., Tubiana, C., and Vincent, J. -B
Abstract: We present the results of the photometric and spectrophotometric properties of the 67P/Churyumov-Gerasimenko nucleus derived with the Optical, Spectroscopic and Infrared Remote Imaging System instrument during the closest fly-by over the comet, which took place on 2015 February 14 at a distance of similar to 6 km from the surface. Several images covering the 0 degrees-33 degrees. phase angle range were acquired, and the spatial resolution achieved was 11 cm pixel(-1). The flown-by region is located on the big lobe of the comet, near the borders of the Ash, Apis and Imhotep regions. Our analysis shows that this region features local heterogeneities at the decimetre scale. We observed difference of reflectance up to 40 per cent between bright spots and sombre regions, and spectral slope variations up to 50 per cent. The spectral reddening effect observed globally on the comet surface by Fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. We note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. In this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. We fitted our data set using the Hapke 2008 photometric model. The region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8 per cent) and it has a high porosity value in the uppermost layers (86 per cent). These results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus.
Published: 2016
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43. Acceleration of individual, decimetre-sized aggregates in the lower coma of comet 67P/Churyumov-Gerasimenko

Author: Agarwal, Jessica, A'Hearn, M. F., Vincent, J. -B, Guettler, C., Hoefner, S., Sierks, H., Tubiana, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., Thomas, N., Agarwal, Jessica, A'Hearn, M. F., Vincent, J. -B, Guettler, C., Hoefner, S., Sierks, H., Tubiana, C., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., and Thomas, N.
Abstract: We present observations of decimetre-sized, likely ice-containing aggregates ejected from a confined region on the surface of comet 67P/Churyumov-Gerasimenko. The images were obtained with the narrow angle camera of the Optical, Spectroscopic, and Infrared Remote Imaging System on board the Rosetta spacecraft in 2016 January when the comet was at 2 au from the Sun outbound from perihelion. We measure the acceleration of individual aggregates through a 2 h image series. Approximately 50 per cent of the aggregates are accelerated away from the nucleus, and 50 per cent towards it, and likewise towards either horizontal direction. The accelerations are up to one order of magnitude stronger than local gravity, and are most simply explained by the combined effect of gas drag accelerating all aggregates upwards, and the recoil force from asymmetric outgassing, either from rotating aggregates with randomly oriented spin axes and sufficient thermal inertia to shift the temperature maximum away from an aggregate's subsolar region, or from aggregates with variable ice content. At least 10 per cent of the aggregates will escape the gravity field of the nucleus and feed the comet's debris trail, while others may fall back to the surface and contribute to the deposits covering parts of the Northern hemisphere. The rocket force plays a crucial role in pushing these aggregates back towards the surface. Our observations show the future back fall material in the process of ejection, and provide the first direct measurement of the acceleration of aggregates in the innermost coma (<2 km) of a comet, where gas drag is still significant.
Published: 2016
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44. Geologic mapping of the Comet 67P/Churyumov-Gerasimenko's Northern hemisphere

Author: Giacomini, L., Massironi, M., El-Maarry, M. R., Penasa, L., Pajola, M., Thomas, N., Lowry, S. C., Barbieri, C., Cremonese, G., Ferri, F., Naletto, G., Bertini, I., La Forgia, F., Lazzarin, M., Marzari, F., Sierks, H., Lamy, P. L., Rodrigo, R., Rickman, Hans, Koschny, D., Keller, H. U., Agarwal, J., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Besse, S., Bodewits, D., Da Deppo, V., Davidsson, Björn, De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Magrin, S., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., Vincent, J. -B, Giacomini, L., Massironi, M., El-Maarry, M. R., Penasa, L., Pajola, M., Thomas, N., Lowry, S. C., Barbieri, C., Cremonese, G., Ferri, F., Naletto, G., Bertini, I., La Forgia, F., Lazzarin, M., Marzari, F., Sierks, H., Lamy, P. L., Rodrigo, R., Rickman, Hans, Koschny, D., Keller, H. U., Agarwal, J., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Besse, S., Bodewits, D., Da Deppo, V., Davidsson, Björn, De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Magrin, S., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., and Vincent, J. -B
Abstract: The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), the scientific imaging system onboard the Rosetta mission, has been acquiring images of the nucleus of the comet 67P/Churyumov-Gerasimenko since 2014 August with a resolution which allows a detailed analysis of its surface. Indeed, data reveal a complex surface morphology which is likely the expression of different processes which occurred at different times on the cometary nucleus. In order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67P Northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. For this purpose, we used narrow-angle camera images acquired in 2014 August and September with a spatial scale ranging from 1.2 to 2.4 m pixel(-1). Several different geologic units have been identified on the basis of their different surface textures, granulometry and morphology. Some of these units are distinctive and localized, whereas others are more common and distributed all over the Northern hemisphere. Moreover, different types of linear features have been distinguished on the basis of their morphology. Some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. The geologic mapping results presented here will allow us to better understand the processes which affected the nucleus' surface and thus the origin and evolutionary history of comet 67P/Churyumov-Gerasimenko.
Published: 2016
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45. Spectrophotometry of the Khonsu region on the comet 67P/Churyumov-Gerasimenko using OSIRIS instrument images

Author: Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Feller, C., Hasselmann, P. H., Sierks, H., El-Maarry, M. R., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Deller, J., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Perna, D., Pommerol, A., Thomas, N., Tubiana, C., Vincent, J. -B, Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Feller, C., Hasselmann, P. H., Sierks, H., El-Maarry, M. R., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Deller, J., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Perna, D., Pommerol, A., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: Our work focuses on the spectrophotometric analysis of selected terrain and bright patches in the Khonsu region on the comet 67P/Churyumov-Gerasimenko. Despite the variety of geological features, their spectrophotometric properties appear to indicate a similar composition. It is noticeable that the smooth areas in Khonsu possess similar spectrophotometric behaviour to some other regions of the comet. We observed bright patches on Khonsu with an estimation of >40 per cent of normal albedo and suggest that they are associated with H2O ice. One of the studied bright patches has been observed to exist on the surface for more than 5 months without a major decay of its size, implying the existence of potential sub-surface icy layers. Its location may be correlated with a cometary outburst during the perihelion passage of the comet in 2015 August, and we interpret it to have triggered the surface modifications necessary to unearth the stratified icy layers beneath the surface. A boulder analysis on Khonsu leads to a power-law index of -3.1 + 0.2/-0.3 suggesting a boulder formation, shaped by varying geological processes for different morphological units.
Published: 2016
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46. Geologic mapping of the Comet 67P/Churyumov-Gerasimenko's Northern hemisphere

Author: Giacomini, L., Massironi, M., El-Maarry, M. R., Penasa, L., Pajola, M., Thomas, N., Lowry, S. C., Barbieri, C., Cremonese, G., Ferri, F., Naletto, G., Bertini, I., La Forgia, F., Lazzarin, M., Marzari, F., Sierks, H., Lamy, P. L., Rodrigo, R., Rickman, Hans, Koschny, D., Keller, H. U., Agarwal, J., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Besse, S., Bodewits, D., Da Deppo, V., Davidsson, Björn, De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Magrin, S., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., Vincent, J. -B, Giacomini, L., Massironi, M., El-Maarry, M. R., Penasa, L., Pajola, M., Thomas, N., Lowry, S. C., Barbieri, C., Cremonese, G., Ferri, F., Naletto, G., Bertini, I., La Forgia, F., Lazzarin, M., Marzari, F., Sierks, H., Lamy, P. L., Rodrigo, R., Rickman, Hans, Koschny, D., Keller, H. U., Agarwal, J., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J. -L, Besse, S., Bodewits, D., Da Deppo, V., Davidsson, Björn, De Cecco, M., Debei, S., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Magrin, S., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Tubiana, C., and Vincent, J. -B
Abstract: The Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS), the scientific imaging system onboard the Rosetta mission, has been acquiring images of the nucleus of the comet 67P/Churyumov-Gerasimenko since 2014 August with a resolution which allows a detailed analysis of its surface. Indeed, data reveal a complex surface morphology which is likely the expression of different processes which occurred at different times on the cometary nucleus. In order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67P Northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. For this purpose, we used narrow-angle camera images acquired in 2014 August and September with a spatial scale ranging from 1.2 to 2.4 m pixel(-1). Several different geologic units have been identified on the basis of their different surface textures, granulometry and morphology. Some of these units are distinctive and localized, whereas others are more common and distributed all over the Northern hemisphere. Moreover, different types of linear features have been distinguished on the basis of their morphology. Some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. The geologic mapping results presented here will allow us to better understand the processes which affected the nucleus' surface and thus the origin and evolutionary history of comet 67P/Churyumov-Gerasimenko.
Published: 2016
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47. Spectrophotometry of the Khonsu region on the comet 67P/Churyumov-Gerasimenko using OSIRIS instrument images

Author: Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Feller, C., Hasselmann, P. H., Sierks, H., El-Maarry, M. R., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Deller, J., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Perna, D., Pommerol, A., Thomas, N., Tubiana, C., Vincent, J. -B, Deshapriya, J. D. P., Barucci, M. A., Fornasier, S., Feller, C., Hasselmann, P. H., Sierks, H., El-Maarry, M. R., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., Deller, J., De Cecco, M., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, R., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Perna, D., Pommerol, A., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: Our work focuses on the spectrophotometric analysis of selected terrain and bright patches in the Khonsu region on the comet 67P/Churyumov-Gerasimenko. Despite the variety of geological features, their spectrophotometric properties appear to indicate a similar composition. It is noticeable that the smooth areas in Khonsu possess similar spectrophotometric behaviour to some other regions of the comet. We observed bright patches on Khonsu with an estimation of >40 per cent of normal albedo and suggest that they are associated with H2O ice. One of the studied bright patches has been observed to exist on the surface for more than 5 months without a major decay of its size, implying the existence of potential sub-surface icy layers. Its location may be correlated with a cometary outburst during the perihelion passage of the comet in 2015 August, and we interpret it to have triggered the surface modifications necessary to unearth the stratified icy layers beneath the surface. A boulder analysis on Khonsu leads to a power-law index of -3.1 + 0.2/-0.3 suggesting a boulder formation, shaped by varying geological processes for different morphological units.
Published: 2016
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48. Summer fireworks on comet 67P

Author: Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, A'Hearn, M. F., Lin, Z. -Y, El-Maarry, M. R., Pajola, M., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Besse, S., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: During its 2 yr mission around comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft had the unique opportunity to follow closely a comet in the most active part of its orbit. Many studies have presented the typical features associated with the activity of the nucleus, such as localized dust and gas jets. Here, we report on series of more energetic transient events observed during the 3 months surrounding the comet's perihelion passage in 2015 August. We detected and characterized 34 outbursts with the Rosetta cameras, one every 2.4 nucleus rotations. We identified three main dust plume morphologies associated with these events: a narrow jet, a broad fan, and more complex plumes featuring both previous types together. These plumes are comparable in scale and temporal variation to what has been observed on other comets. We present a map of the outbursts' source locations, and discuss the associated topography. We find that the spatial distribution sources on the nucleus correlate well with morphological region boundaries, especially in areas marked by steep scarps or cliffs. Outbursts occur either in the early morning or shortly after the local noon, indicating two potential processes: morning outbursts may be triggered by thermal stresses linked to the rapid change of temperature; afternoon events are most likely related to the diurnal or seasonal heat wave reaching volatiles buried under the first surface layer. In addition, we propose that some events can be the result of a completely different mechanism, in which most of the dust is released upon the collapse of a cliff.
Published: 2016
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49. Comparative study of water ice exposures on cometary nuclei using multispectral imaging data

Author: Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., Tubiana, C., Oklay, N., Sunshine, J. M., Pajola, M., Pommerol, A., Vincent, J. -B, Mottola, S., Sierks, H., Fornasier, S., Barucci, M. A., Preusker, F., Scholten, F., Lara, L. M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Bertaux, J. -L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B. J. R., Debei, S., De Cecco, M., Deller, J., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Thomas, N., and Tubiana, C.
Abstract: Deep Impact, EPOXI and Rosetta missions visited comets 9P/Tempel 1, 103P/Hartley 2 and 67P/Churyumov-Gerasimenko, respectively. Each of these three missions was equipped with both multispectral imagers and infrared spectrometers. Bright blue features containing water ice were detected in each of these comet nuclei. We analysed multispectral properties of enriched water ice features observed via Optical, Spectroscopic, and Infrared Remote Imaging System narrow angle camera on comet 67P in the wavelength range of 260-1000 nm and then compared with multispectral data of water ice deposits observed on comets 9P and 103P. We characterize the UV/VIS properties of water-ice-rich features observed on the nuclei of these three comets. When compared to the average surface of each comet, our analysis shows that the water ice deposits seen on comet 9P are similar to the clustered water-ice-rich features seen on comet 67P, while the water ice deposit seen on comet 103P is more akin to two large isolated water-ice-rich features seen on comet 67P. Our results indicate that the water ice deposit observed on comet 103P contains more water ice than the water-ice-rich features observed on comets 9P and 67P, proportionally to the average surface of each nucleus.
Published: 2016
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50. Sublimation of icy aggregates in the coma of comet 67P/Churyumov-Gerasimenko detected with the OSIRIS cameras on board Rosetta

Author: Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Vincent, J. -B, Agarwal, J., A'Hearn, M. F., Bertini, I., Bodewits, D., Sierks, H., Li, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Cremonese, G., Da Deppo, V., Davidsson, Björn, Debei, S., Deller, J., De Cecco, M., Frattin, E., El-Maarry, M. R., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Hoefner, S., Hofmann, M., Hu, X., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Lowry, S., Marzari, F., Masoumzadeh, N., Massironi, M., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Pommerol, A., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Beginning in 2014 March, the OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) cameras began capturing images of the nucleus and coma (gas and dust) of comet 67P/Churyumov-Gerasimenko using both the wide angle camera (WAC) and the narrow angle camera (NAC). The many observations taken since July of 2014 have been used to study the morphology, location, and temporal variation of the comet's dust jets. We analysed the dust monitoring observations shortly after the southern vernal equinox on 2015 May 30 and 31 with the WAC at the heliocentric distance R-h = 1.53 AU, where it is possible to observe that the jet rotates with the nucleus. We found that the decline of brightness as a function of the distance of the jet is much steeper than the background coma, which is a first indication of sublimation. We adapted a model of sublimation of icy aggregates and studied the effect as a function of the physical properties of the aggregates (composition and size). The major finding of this paper was that through the sublimation of the aggregates of dirty grains (radius a between 5 and 50 mu m) we were able to completely reproduce the radial brightness profile of a jet beyond 4 km from the nucleus. To reproduce the data, we needed to inject a number of aggregates between 8.5 x 10(13) and 8.5 x 10(10) for a = 5 and 50 mu m, respectively, or an initial mass of H2O ice around 22 kg.
Published: 2016
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