Author: "Cremonese G" / Publisher: uppsala universitet, teoretisk astrofysik - Searchworks@Jio Institute Digital Library Search Results

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91 results on '"Cremonese G"'

1. Seasonal variations in source regions of the dust jets on comet 67P/Churyumov-Gerasimenko

Author: Lai, I-L, Ip, W-H, Lee, J-C, Lin, Z. Y., Vincent, J-B, Oklay, N., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J-L, Bertini, I, Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V, Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Güttler, C., Hofmann, M., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J-R, Kührt, E., Küppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Tubiana, C., Thomas, N., Lai, I-L, Ip, W-H, Lee, J-C, Lin, Z. Y., Vincent, J-B, Oklay, N., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Agarwal, J., Barucci, M. A., Bertaux, J-L, Bertini, I, Bodewits, D., Boudreault, S., Cremonese, G., Da Deppo, V, Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Güttler, C., Hofmann, M., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J-R, Kührt, E., Küppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Shi, X., Tubiana, C., and Thomas, N.
Abstract: Aims: We investigate the surface distribution of the source regions of dust jets on comet 67P/Churyumov-Gerasimenko as a function of time. Methods: The dust jet source regions were traced by the comprehensive imaging data set provided by the OSIRIS scientific camera. Results: We show in detail how the projected footpoints of the dust jets and hence the outgassing zone would move in consonance with the sunlit belt. Furthermore, a number of source regions characterized by repeated jet activity might be the result of local topographical variations or compositional heterogeneities. Conclusions: The spatial and temporal variations in source regions of the dust jets are influenced significantly by the seasonal effect. The strong dependence on the solar zenith angle and local time could be related to the gas sublimation process driven by solar insolation on a surface layer of low thermal inertia.
Published: 2019
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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. The phase function and density of the dust observed at comet 67P/Churyumov-Gerasimenko

Author: Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., Tubiana, C., Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., and Tubiana, C.
Abstract: The OSIRIS camera onboard Rosetta measured the phase function of both the coma dust and the nucleus. The two functions have a very different slope versus the phase angle. Here, we show that the nucleus phase function should be adopted to convert the brightness to the size of dust particles larger than 2.5 mm only. This makes the dust bursts observed close to Rosetta by OSIRIS, occurring about every hour, consistent with the fragmentation on impact with Rosetta of parent particles, whose flux agrees with the dust flux observed by GIADA. OSIRIS also measured the antisunward acceleration of the fragments, thus providing the first direct measurement of the solar radiation force acting on the dust fragments and thus of their bulk density, excluding any measurable rocket effect by the ice sublimation from the dust. The obtained particle density distribution has a peak matching the bulk density of most COSIMA particles, and represents a subset of the density distribution measured by GIADA. This implies a bias in the elemental abundances measured by COSIMA, which thus are consistent with the 67P dust mass fractions inferred by GIADA, i.e. (38 +/- 8) per cent of hydrocarbons versus the (62 +/- 8) per cent of sulphides and silicates.
Published: 2018
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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
Full Text: View/download PDF

6. The phase function and density of the dust observed at comet 67P/Churyumov-Gerasimenko

Author: Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., Tubiana, C., Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., and Tubiana, C.
Abstract: The OSIRIS camera onboard Rosetta measured the phase function of both the coma dust and the nucleus. The two functions have a very different slope versus the phase angle. Here, we show that the nucleus phase function should be adopted to convert the brightness to the size of dust particles larger than 2.5 mm only. This makes the dust bursts observed close to Rosetta by OSIRIS, occurring about every hour, consistent with the fragmentation on impact with Rosetta of parent particles, whose flux agrees with the dust flux observed by GIADA. OSIRIS also measured the antisunward acceleration of the fragments, thus providing the first direct measurement of the solar radiation force acting on the dust fragments and thus of their bulk density, excluding any measurable rocket effect by the ice sublimation from the dust. The obtained particle density distribution has a peak matching the bulk density of most COSIMA particles, and represents a subset of the density distribution measured by GIADA. This implies a bias in the elemental abundances measured by COSIMA, which thus are consistent with the 67P dust mass fractions inferred by GIADA, i.e. (38 +/- 8) per cent of hydrocarbons versus the (62 +/- 8) per cent of sulphides and silicates.
Published: 2018
Full Text: View/download PDF

7. The phase function and density of the dust observed at comet 67P/Churyumov-Gerasimenko

Author: Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., Tubiana, C., Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., and Tubiana, C.
Abstract: The OSIRIS camera onboard Rosetta measured the phase function of both the coma dust and the nucleus. The two functions have a very different slope versus the phase angle. Here, we show that the nucleus phase function should be adopted to convert the brightness to the size of dust particles larger than 2.5 mm only. This makes the dust bursts observed close to Rosetta by OSIRIS, occurring about every hour, consistent with the fragmentation on impact with Rosetta of parent particles, whose flux agrees with the dust flux observed by GIADA. OSIRIS also measured the antisunward acceleration of the fragments, thus providing the first direct measurement of the solar radiation force acting on the dust fragments and thus of their bulk density, excluding any measurable rocket effect by the ice sublimation from the dust. The obtained particle density distribution has a peak matching the bulk density of most COSIMA particles, and represents a subset of the density distribution measured by GIADA. This implies a bias in the elemental abundances measured by COSIMA, which thus are consistent with the 67P dust mass fractions inferred by GIADA, i.e. (38 +/- 8) per cent of hydrocarbons versus the (62 +/- 8) per cent of sulphides and silicates.
Published: 2018
Full Text: View/download PDF

8. 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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9. The phase function and density of the dust observed at comet 67P/Churyumov-Gerasimenko

Author: Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., Tubiana, C., Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., and Tubiana, C.
Abstract: The OSIRIS camera onboard Rosetta measured the phase function of both the coma dust and the nucleus. The two functions have a very different slope versus the phase angle. Here, we show that the nucleus phase function should be adopted to convert the brightness to the size of dust particles larger than 2.5 mm only. This makes the dust bursts observed close to Rosetta by OSIRIS, occurring about every hour, consistent with the fragmentation on impact with Rosetta of parent particles, whose flux agrees with the dust flux observed by GIADA. OSIRIS also measured the antisunward acceleration of the fragments, thus providing the first direct measurement of the solar radiation force acting on the dust fragments and thus of their bulk density, excluding any measurable rocket effect by the ice sublimation from the dust. The obtained particle density distribution has a peak matching the bulk density of most COSIMA particles, and represents a subset of the density distribution measured by GIADA. This implies a bias in the elemental abundances measured by COSIMA, which thus are consistent with the 67P dust mass fractions inferred by GIADA, i.e. (38 +/- 8) per cent of hydrocarbons versus the (62 +/- 8) per cent of sulphides and silicates.
Published: 2018
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10. 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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11. The phase function and density of the dust observed at comet 67P/Churyumov-Gerasimenko

Author: Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., Tubiana, C., Fulle, Marco, Bertini, I., Della Corte, V., Guttler, C., Ivanovski, S., La Forgia, F., Lasue, J., Levasseur-Regourd, A. C., Marzari, F., Moreno, F., Mottola, S., Naletto, G., Palumbo, P., Rinaldi, G., Rotundi, A., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Barucci, M. A., Bertaux, J. -L, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Hviid, H. S., Ip, W. H., Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuhrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Shi, X., Thomas, N., and Tubiana, C.
Abstract: The OSIRIS camera onboard Rosetta measured the phase function of both the coma dust and the nucleus. The two functions have a very different slope versus the phase angle. Here, we show that the nucleus phase function should be adopted to convert the brightness to the size of dust particles larger than 2.5 mm only. This makes the dust bursts observed close to Rosetta by OSIRIS, occurring about every hour, consistent with the fragmentation on impact with Rosetta of parent particles, whose flux agrees with the dust flux observed by GIADA. OSIRIS also measured the antisunward acceleration of the fragments, thus providing the first direct measurement of the solar radiation force acting on the dust fragments and thus of their bulk density, excluding any measurable rocket effect by the ice sublimation from the dust. The obtained particle density distribution has a peak matching the bulk density of most COSIMA particles, and represents a subset of the density distribution measured by GIADA. This implies a bias in the elemental abundances measured by COSIMA, which thus are consistent with the 67P dust mass fractions inferred by GIADA, i.e. (38 +/- 8) per cent of hydrocarbons versus the (62 +/- 8) per cent of sulphides and silicates.
Published: 2018
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12. Investigating the physical properties of outbursts on comet 67P/Churyumov-Gerasimenko

Author: Lin, Zhong-Yi, Knollenberg, J., Vincent, J. -B, A'Hearn, M. F., Ip, W-H, Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., Mottola, S., Bodewits, D., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Deller, J., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Jorda, L., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lai, I. -L, Lara, L. M., Lazzarin, M., Lee, J-C, Lopez-Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Ott, T., Drolshagen, E., Shi, X., Thomas, N., Tubiana, C., Lin, Zhong-Yi, Knollenberg, J., Vincent, J. -B, A'Hearn, M. F., Ip, W-H, Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., Mottola, S., Bodewits, D., Agarwal, J., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Deller, J., Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Jorda, L., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lai, I. -L, Lara, L. M., Lazzarin, M., Lee, J-C, Lopez-Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Ott, T., Drolshagen, E., Shi, X., Thomas, N., and Tubiana, C.
Abstract: Cometary outbursts on several comets have been observed both by ground-based telescopes and by in situ instruments on spacecraft. However, the mechanism behind these phenomena and their physical properties are still unclear. The optical, spectrocopic and infrared remote imaging system (OSIRIS) onboard the Rosetta spacecraft provided first-hand information on the outbursts from comet 67P/Churyumov-Gerasimenko during its perihelion passage in 2015. The physical properties of the outbursts can be investigated by examining the time series of these high-resolution images. An analysis is made of the wide- and narrow-angle images obtained during the monitoring of the outburst sequences, which occurred between July and September in 2015. A ring-masking technique is used to calculate the excess brightness of the outbursts. The ejected mass and expansion velocity of the outbursts is estimated from differences in images made with the same filter (orange filter). The calculated excess brightness from these outburst plumes ranges from a few per cent to 28 per cent. In some major outbursts, the brightness contribution from the outburst plume can be one or two times higher than that of the typical coma jet activities. The strongest event was the perihelion outburst detected just a few hours before perihelion. The mass ejection rate during a generic outburst could reach a few per cent of the steady-state value of the dust coma. Transient events are detected by studying the brightness slope of the outburst plume with continuous streams of outflowing gas and dust triggered by driving mechanisms, as yet not understood, which remain active for several minutes to less than a few hours.
Published: 2017
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13. Thermal modelling of water activity on comet 67P/Churyumov-Gerasimenko with global dust mantle and plural dust-to-ice ratio

Author: Hu, X., Shi, X., Sierks, H., Blum, J., Oberst, J., Fulle, M., Kuehrt, E., Guettler, C., Gundlach, B., Keller, H. U., Mottola, S., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Buettner, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Gutierrez-Marques, P., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. R., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Richards, M. L., Ripken, J., Thomas, N., Tubiana, C., Vincent, J. -B, Hu, X., Shi, X., Sierks, H., Blum, J., Oberst, J., Fulle, M., Kuehrt, E., Guettler, C., Gundlach, B., Keller, H. U., Mottola, S., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Boudreault, S., Buettner, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Gutierrez-Marques, P., Hall, I., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. R., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Richards, M. L., Ripken, J., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: We perform a thermo-physical analysis on water activity of comet 67P/Churyumov-Gerasimenko (67P). The sublimation of water is assumed to occur from beneath a global, desiccated dust mantle over the irregular-shaped nucleus. The concept of two thermal models, the recipe of model formulation and the strategy of application to comet 67P are described. For an accurate and efficient evaluation of energy input by insolation and self-heating over the nucleus, a Landscape data base is devised based on polyhedral shape models of the nucleus. We apply the thermal models to investigate the impact of certain parameters of nucleus properties on water production. It is found that the measured water production of 67P can be overall attributed to sublimation of water ice with a mass abundance of a few to 10 per cent beneath a uniform dust mantle of several millimetres to one centimetre in thickness. Insofar as 67P is concerned, we argue against the necessity to invoke assumptions on localized water activity, or on the distinction of active/dormant surface areas.
Published: 2017
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14. The highly active Anhur-Bes regions in the 67P/Churyumov-Gerasimenko comet : results from OSIRIS/ROSETTA observations

Author: Fornasier, S., Feller, C., Lee, J. -C, Ferrari, S., Massironi, M., Hasselmann, P. H., Deshapriya, J. D. P., Barucci, M. A., El-Maarry, M. R., Giacomini, L., Mottola, S., Keller, H. U., Ip, W. -H, Lin, Z. -Y, Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, R., Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Pajola, M., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, Fornasier, S., Feller, C., Lee, J. -C, Ferrari, S., Massironi, M., Hasselmann, P. H., Deshapriya, J. D. P., Barucci, M. A., El-Maarry, M. R., Giacomini, L., Mottola, S., Keller, H. U., Ip, W. -H, Lin, Z. -Y, Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Agarwal, J., A'Hearn, M., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Jorda, L., Knollenberg, J., Kovacs, G., Kramm, R., Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Pajola, M., Shi, X., Thomas, N., Toth, I., Tubiana, C., and Vincent, J. -B
Abstract: The Southern hemisphere of the 67P/Churyumov-Gerasimenko comet has become visible from Rosetta only since 2015 March. It was illuminated during the perihelion passage and therefore it contains the regions that experienced the strongest heating and erosion rates, thus exposing the sub-surface most pristine material. In this work we investigate, thanks to the OSIRIS images, the geomorphology, the spectrophotometry and some transient events of two Southern hemisphere regions: Anhur and part of Bes. Bes is dominated by outcropping consolidated terrain covered with fine particle deposits, while Anhur appears strongly eroded with elongated canyon-like structures, scarp retreats, different kinds of deposits and degraded sequences of strata indicating a pervasive layering. We discovered a new 140 m long and 10 m high scarp formed in the Anhur-Bes boundary during/after the perihelion passage, close to the area where exposed CO2 and H2O ices were previously detected. Several jets have been observed originating from these regions, including the strong perihelion outburst, an active pit and a faint optically thick dust plume. We identify several areas with a relatively bluer slope (i.e. a lower spectral slope value) than their surroundings, indicating a surface composition enriched with some water ice. These spectrally bluer areas are observed especially in talus and gravitational accumulation deposits where freshly exposed material had fallen from nearby scarps and cliffs. The investigated regions become spectrally redder beyond 2 au outbound when the dust mantle became thicker, masking the underlying ice-rich layers.
Published: 2017
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15. Modelling of the outburst on 2015 July 29 observed with OSIRIS cameras in the Southern hemisphere of comet 67P/Churyumov-Gerasimenko

Author: Gicquel, A., Rose, M., Vincent, J. -B, Davidsson, B., Bodewits, D., A'Hearn, M. F., Agarwal, J., Fougere, N., Sierks, H., Bertini, I., Lin, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., 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., Kuppers, 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., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Gicquel, A., Rose, M., Vincent, J. -B, Davidsson, B., Bodewits, D., A'Hearn, M. F., Agarwal, J., Fougere, N., Sierks, H., Bertini, I., Lin, Z. -Y, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, Keller, H. U., Barucci, M. A., Bertaux, J. -L, Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., 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., Kuppers, 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., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: Images of the nucleus and the coma (gas and dust) of comet 67P/Churyumov-Gerasimenko have been acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) cameras since 2014 March using both the wide-angle camera and the narrow-angle camera (NAC). We use images from the NAC camera to study a bright outburst observed in the Southern hemisphere on 2015 July 29. The high spatial resolution of the NAC is needed to localize the source point of the outburst on the surface of the nucleus. The heliocentric distance is 1.25 au and the spacecraft-comet distance is 186 km. Aiming to better understand the physics that led to the outgassing, we used the Direct Simulation Monte Carlo method to study the gas flow close to the nucleus and the dust trajectories. The goal is to understand the mechanisms producing the outburst. We reproduce the opening angle of the outburst in the model and constrain the outgassing ratio between the outburst source and the local region. The outburst is in fact a combination of both gas and dust, in which the active surface is approximately 10 times more active than the average rate found in the surrounding areas. We need a number of dust particles 7.83 x 10(11) to 6.90 x 10(15) (radius 1.97-185 mu m), which correspond to a mass of dust (220-21) x 10(3) kg.
Published: 2017
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16. Post-perihelion photometry of dust grains in the coma of 67P Churyumov-Gerasimenko

Author: Frattin, E., Cremonese, G., Simioni, E., Bertini, I., Lazzarin, M., Ott, T., Drolshagen, E., La Forgia, F., 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, Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Ferrari, S., Ferri, F., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Lucchetti, A., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Penasa, L., Shi, X., Thomas, N., Tubiana, C., Vincent, J. -B, Frattin, E., Cremonese, G., Simioni, E., Bertini, I., Lazzarin, M., Ott, T., Drolshagen, E., La Forgia, F., 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, Da Deppo, V., Davidsson, Björn, Debei, S., De Cecco, M., Deller, J., Ferrari, S., Ferri, F., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kramm, J. -R, Kuehrt, E., Kuppers, M., Lara, L. M., Lopez Moreno, J. J., Lucchetti, A., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Penasa, L., Shi, X., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: We present a photometric analysis of individual dust grains in the coma of comet 67P/Churyumov-Gerasimenko using OSIRIS images taken from 2015 July to 2016 January. We analysed a sample of 555 taken during 18 d at heliocentric distances ranging between 1.25 and 2.04 au and at nucleocentric distances between 80 and 437 km. An automated method to detect the tracks was specifically developed. The images were taken by OSIRIS NAC in four different filters: Near-IR (882 nm), Orange (649 nm), FarOrange (649 nm) and Blue (480 nm). It was not always possible to recognize all the grains in the four filters, hence we measured the spectral slope in two wavelengths ranges: in the interval [480-649] nm, for 1179 grains, and in the interval [649-882] nm, for 746 grains. We studied the evolution of the two populations' average spectral slopes. The data result scattered around the average value in the range [480-649] nm, while in the [649-882] nm we observe a slight decreasing moving away from the Sun as well as a slight increasing with the nucleocentric distance. A spectrophotometric analysis was performed on a subsample of 339 grains. Three major groups were defined, based on the spectral slope between [535-882] nm: (i) the steep spectra that may be related with organic material, (ii) the spectra with an intermediate slope, likely a mixture of silicates and organics and (iii) flat spectra that may be associated with a high abundance of water ice.
Published: 2017
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17. Characterization of dust aggregates in the vicinity of the Rosetta spacecraft

Author: Guettler, C., Hasselmann, P. H., Li, Y., Fulle, M., Tubiana, C., Kovacs, G., Agarwal, J., Sierks, H., Fornasier, S., Hofmann, M., Marques, P. Gutierrez, Ott, T., Drolshagen, E., Bertini, I., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bodewits, D., Bertaux, J. -L, Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Geiger, B., Groussin, O., Gutierrez, P. J., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Shi, X., Thomas, N., Vincent, J. -B, Guettler, C., Hasselmann, P. H., Li, Y., Fulle, M., Tubiana, C., Kovacs, G., Agarwal, J., Sierks, H., Fornasier, S., Hofmann, M., Marques, P. Gutierrez, Ott, T., Drolshagen, E., Bertini, I., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bodewits, D., Bertaux, J. -L, Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Geiger, B., Groussin, O., Gutierrez, P. J., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pajola, M., Shi, X., Thomas, N., and Vincent, J. -B
Abstract: In a Rosetta/OSIRIS imaging activity in 2015 June, we have observed the dynamic motion of particles close to the spacecraft. Due to the focal setting of the OSIRIS wide angle camera, these particles were blurred, which can be used to measure their distances to the spacecraft. We detected 109 dust aggregates over a 130 min long sequence, and find that their sizes are around a millimetre and their distances cluster between 2 and 40 m from the spacecraft. Their number densities are about a factor 10 higher than expected for the overall coma and highly fluctuating. Their velocities are small compared to the spacecraft orbital motion and directed away from the spacecraft, towards the comet. From this we conclude that they have interacted with the spacecraft and assess three possible scenarios. In the likeliest of the three scenarios, centimetre-sized aggregates collide with the spacecraft and we would observe the fragments. Ablation of a dust layer on the spacecraft's z panel (remote instrument viewing direction) when rotated towards the Sun is a reasonable alternative. We could also measure an acceleration for a subset of 18 aggregates, which is directed away from the Sun and can be explain by a rocket effect, which requires a minimum ice fraction of the order of 0.1 per cent.
Published: 2017
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18. Constraints on cometary surface evolution derived from a statistical analysis of 67P's topography

Author: Vincent, J. -B, Hviid, S. F., Mottola, S., Kuehrt, E., Preusker, F., Scholten, F., Keller, H. U., Oklay, N., de Niem, D., Davidsson, B., Fulle, M., Pajola, M., Hofmann, M., Hu, X., Rickman, Hans, Lin, Z. -Y, Feller, C., Gicquel, A., Boudreault, S., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Penasa, L., Shi, X., Thomas, N., Toth, I., Tubiana, C., Vincent, J. -B, Hviid, S. F., Mottola, S., Kuehrt, E., Preusker, F., Scholten, F., Keller, H. U., Oklay, N., de Niem, D., Davidsson, B., Fulle, M., Pajola, M., Hofmann, M., Hu, X., Rickman, Hans, Lin, Z. -Y, Feller, C., Gicquel, A., Boudreault, S., Sierks, H., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Groussin, O., Gutierrez, P. J., Gutierrez-Marquez, P., Guettler, C., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Penasa, L., Shi, X., Thomas, N., Toth, I., and Tubiana, C.
Abstract: We present a statistical analysis of the distribution of large-scale topographic features on comet 67P/Churyumov-Gerasimenko. We observe that the cumulative cliff height distribution across the surface follows a power law with a slope equal to -1.69 +/- 0.02. When this distribution is studied independently for each region, we find a good correlation between the slope of the power law and the orbital erosion rate of the surface. For instance, the Northern hemisphere topography is dominated by structures on the 100 m scale, while the Southern hemisphere topography, illuminated at perihelion, is dominated by 10 m scale terrain features. Our study suggests that the current size of a cliff is controlled not only by material cohesion but also by the dominant erosional process in each region. This observation can be generalized to other comets, where we argue that primitive nuclei are characterized by the presence of large cliffs with a cumulative height-power index equal to or above -1.5, while older, eroded cometary surfaces have a power index equal to or below -2.3. In effect, our model shows that a measure of the topography provides a quantitative assessment of a comet's erosional history, that is, its evolutionary age.
Published: 2017
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19. A three-dimensional modelling of the layered structure of comet 67P/Churyumov-Gerasimenko

Author: Penasa, L., Massironi, M., Naletto, G., Simioni, E., Ferrari, S., Pajola, M., Lucchetti, A., Preusker, F., Scholten, F., Jorda, L., Gaskell, R., Ferri, F., Marzari, F., Davidsson, B., Mottola, 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., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Feller, C., Fornasier, S., Frattin, E., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W. H., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., La Forgia, F., Lara, L. M., Lazzarin, M., Lee, J. -C, Lopez Moreno, J. J., Oklay, N., Shi, X., Thomas, N., Tubiana, C., Vincent, J. B., Penasa, L., Massironi, M., Naletto, G., Simioni, E., Ferrari, S., Pajola, M., Lucchetti, A., Preusker, F., Scholten, F., Jorda, L., Gaskell, R., Ferri, F., Marzari, F., Davidsson, B., Mottola, 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., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Feller, C., Fornasier, S., Frattin, E., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W. H., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., La Forgia, F., Lara, L. M., Lazzarin, M., Lee, J. -C, Lopez Moreno, J. J., Oklay, N., Shi, X., Thomas, N., Tubiana, C., and Vincent, J. B.
Abstract: We provide a three-dimensional model of the inner layered structure of comet 67P based on the hypothesis of an extended layering independently wrapping each lobe. A large set of terrace orientations was collected on the latest shape model and then used as a proxy for the local orientation of the surfaces of discontinuity which defines the layers. We modelled the terraces as a family of concentric ellipsoidal shells with fixed axis ratios, producing a model that is completely defined by just eight free parameters. Each lobe of 67P has been modelled independently, and the two sets of parameters have been estimated by means of non-linear optimization of the measured terrace orientations. The proposed model is able to predict the orientation of terraces, the elongation of cliffs, the linear traces observed in the Wosret and Hathor regions and the peculiar alignment of boulder-like features which has been observed in the Hapi region, which appears to be related to the inner layering of the big lobe. Our analysis allowed us to identify a plane of junction between the two lobes, further confirming the independent nature of the lobes. Our layering models differ from the best-fitting topographic ellipsoids of the surface, demonstrating that the terraces are aligned to an internal structure of discontinuities, which is unevenly exposed on the surface, suggesting a complex history of localized material removal from the nucleus.
Published: 2017
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20. The opposition effect of 67P/Churyumov-Gerasimenko on post-perihelion Rosetta images

Author: Hasselmann, P. H., Barucci, M. A., Fornasier, S., Feller, C., Deshapriya, J. D. P., Fulchignoni, M., Jost, B., 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., De Cecco, M., Deller, J., Fulle, M., Gaskell, R. W., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, R., Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pommerol, A., Thomas, N., Tubiana, C., Vincent, J. -B, Hasselmann, P. H., Barucci, M. A., Fornasier, S., Feller, C., Deshapriya, J. D. P., Fulchignoni, M., Jost, B., 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., De Cecco, M., Deller, J., Fulle, M., Gaskell, R. W., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Keller, H. U., Knollenberg, J., Kovacs, G., Kramm, R., Kuehrt, E., Kuppers, M., Lara, M. L., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Mottola, S., Naletto, G., Oklay, N., Pommerol, A., Thomas, N., Tubiana, C., and Vincent, J. -B
Abstract: High-resolution OSIRIS/Rosetta images of 67P/Churyumov-Gerasimenko acquired on the night run of 2016 April 9-10 show, at large scale, an opposition effect (OE) spot sweeping across Imhotep as the phase angle ranges from 0 degrees to 17 degrees. In this work, we fitted the phase curve of the whole surface imaged as well as three particular features using both the linear-exponential and Hapke models. These features encompass different types of spectral behaviour: a circular mesa, one venous structure and an assemblage of bright spots, going from red to blue colours. Both the Hapke and linear-exponential parameters indicate a stepwise sharpening of the OE from bright spots to circular mesa. Yet a very broad nonlinear phase curve is verified and no sign of sharp OE associated with a coherent-backscattering mechanism is observed. We estimate that the 67P surface is dominated by opaque, desiccated and larger-than-wavelength irregular grains. Veins and bright spots display photometric properties consistent with surfaces becoming slightly brighter as they are enriched by high-albedo ice grains. We also report the estimation of normal albedo for all cometary regions observed throughout the image sequence. Comparison to pre-perihelion results indicates that far better insolation of northern brighter regions, i.e. Hapi, Hathor and Seth, is sufficient to explain mismatches on the photometric parameters. However, metre-scale photometric analysis of the Imhotep-Ash boundary area advocates for mild darkening (<7 per cent) of the surface at local scale.
Published: 2017
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21. Seasonal mass transfer on the nucleus of comet 67P/Chuyumov-Gerasimenko

Author: Keller, H. U., Mottola, S., Hviid, S. F., Agarwal, J., Kuehrt, E., Skorov, Y., Otto, K., Vincent, J. -B, Oklay, N., Schroeder, S. E., Davidsson, Björn, Pajola, M., Shi, X., Bodewits, D., Toth, I., Preusker, F., Scholten, F., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, H., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Ip, W. -H, Jorda, L., Knollenberg, J., Kramm, J. R., Kuppers, M., Lara, L. -M, Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Tubiana, C., Thomas, N., Keller, H. U., Mottola, S., Hviid, S. F., Agarwal, J., Kuehrt, E., Skorov, Y., Otto, K., Vincent, J. -B, Oklay, N., Schroeder, S. E., Davidsson, Björn, Pajola, M., Shi, X., Bodewits, D., Toth, I., Preusker, F., Scholten, F., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, H., A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Guettler, C., Hofmann, M., Ip, W. -H, Jorda, L., Knollenberg, J., Kramm, J. R., Kuppers, M., Lara, L. -M, Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Naletto, G., Tubiana, C., and Thomas, N.
Abstract: We collect observational evidence that supports the scheme of mass transfer on the nucleus of comet 67P/Churyumov-Gerasimenko. The obliquity of the rotation axis of 67P causes strong seasonal variations. During perihelion the southern hemisphere is four times more active than the north. Northern territories are widely covered by granular material that indicates back fall originating from the active south. Decimetre sized chunks contain water ice and their trajectories are influenced by an antisolar force instigated by sublimation. OSIRIS observations suggest that up to 20 per cent of the particles directly return to the nucleus surface taking several hours of traveltime. The back fall covered northern areas are active if illuminated but produce mainly water vapour. The decimetre chunks from the nucleus surface are too small to contain more volatile compounds such as CO2 or CO. This causes a north-south dichotomy of the composition measurements in the coma. Active particles are trapped in the gravitational minimum of Hapi during northern winter. They are 'shock frozen' and only re-activated when the comet approaches the sun after its aphelion passage. The insolation of the big cavity is enhanced by self-heating, i.e. reflection and IR radiation from the walls. This, together with the pristinity of the active back fall, explains the early observed activity of the Hapi region. Sobek may be a role model for the consolidated bottom of Hapi. Mass transfer in the case of 67P strongly influences the evolution of the nucleus and the interpretation of coma measurements.
Published: 2017
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22. The scattering phase function of comet 67P/Churyumov-Gerasimenko coma as seen from the Rosetta/OSIRIS instrument

Author: Bertini, I., La Forgia, F., Tubiana, C., Guettler, C., Fulle, M., Moreno, F., Frattin, E., Kovacs, G., Pajola, M., 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, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Drolshagen, E., Ferrari, S., Ferri, F., Fornasier, S., Gicquel, A., Groussin, O., Gutierrez, P. J., Hasselmann, P. H., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Lucchetti, A., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Ott, T., Penasa, L., Thomas, N., Vincent, J. -B, Bertini, I., La Forgia, F., Tubiana, C., Guettler, C., Fulle, M., Moreno, F., Frattin, E., Kovacs, G., Pajola, M., 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, Bodewits, D., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Drolshagen, E., Ferrari, S., Ferri, F., Fornasier, S., Gicquel, A., Groussin, O., Gutierrez, P. J., Hasselmann, P. H., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., Lara, L. M., Lazzarin, M., Lin, Z. -Y, Lopez Moreno, J. J., Lucchetti, A., Marzari, F., Massironi, M., Mottola, S., Naletto, G., Oklay, N., Ott, T., Penasa, L., Thomas, N., and Vincent, J. -B
Abstract: The study of dust, the most abundant material in cometary nuclei, is pivotal in understanding the original materials forming the Solar system. Measuring the coma phase function provides a tool to investigate the nature of cometary dust. Rosetta/OSIRIS sampled the coma phase function of comet 67P/Churyumov-Gerasimenko, covering a large phase angle range in a small amount of time. Twelve series were acquired in the period from 2015 March to 2016 February for this scientific purpose. These data allowed, after stray light removal, measuring the phase function shape, its reddening, and phase reddening while varying heliocentric and nucleocentric distances. Despite small dissimilarities within different series, we found a constant overall shape. The reflectance has a u-shape with minimum at intermediate phase angles, reaching similar values at the smallest and largest phase angle sampled. The comparison with cometary phase functions in literature indicates OSIRIS curves being consistent with the ones found in many other single comets. The dust has a negligible phase reddening at alpha < 90 degrees, indicating a coma dominated by single scattering. We measured a reddening of [11-14] %/100 nm between 376 and 744 nm. No trend with heliocentric or nucleocentric distance was found, indicating the coma doesn't change its spectrum with time. These results are consistent with single coma grains and close-nucleus coma photometric results. Comparison with nucleus photometry indicates a different backscattering phase function shape and similar reddening values only at alpha < 30 degrees. At larger phase angles, the nucleus becomes significantly redder than the coma.
Published: 2017
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23. Distance determination method of dust particles using Rosetta OSIRIS NAC and WAC data

Author: Drolshagen, E., Ott, T., Koschny, D., Guetler, C., Tubiana, C., Agarwal, J., Sierks, H., Barbieri, C., Lamy, P. I., Rodrigo, R., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Feller, C., 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., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., Thomas, N., Poppe, B., Drolshagen, E., Ott, T., Koschny, D., Guetler, C., Tubiana, C., Agarwal, J., Sierks, H., Barbieri, C., Lamy, P. I., Rodrigo, R., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Feller, C., 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., Kuppers, M., Lara, L. M., Lazzarin, M., Lopez Moreno, J. J., Marzari, F., Naletto, G., Oklay, N., Shi, X., Thomas, N., and Poppe, B.
Abstract: The ESA Rosetta spacecraft has been tracking its target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, in close vicinity for over two years. It hosts the OSIRIS instruments: the Optical, Spectroscopic, and Infrared Remote Imaging System composed of two cameras, see e.g. Keller et al. (2007). In some imaging sequences dedicated to observe dust particles in the comet's coma, the two cameras took images at the same time. The aim of this work is to use these simultaneous double camera observations to calculate the dust particles' distance to the spacecraft. As the two cameras are mounted on the spacecraft with an offset of 70 cm, the distance of particles observed by both cameras can be determined by a shift of the particles' apparent trails on the images. This paper presents first results of the ongoing work, introducing the distance determination method for the OSIRIS instrument and the analysis of an example particle. We note that this method works for particles in the range of about 500-6000 m from the spacecraft.
Published: 2017
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24. Thermophysics of fractures on comet 67P/Churyumov-Gerasimenko

Author: Höfner, S., Vincent, J. -B, Blum, J., Davidsson, Björn J. R., Sierks, H., El-Maarry, M. R., Deller, J., Hofmann, M., Hu, X., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J.-L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutiérrez, P. J., Gutiérrez-Marqués, P., Güttler, C., Hviid, S. F., Ip, W.-H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kührt, E., Küppers, M., La Forgia, F., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Michalik, H., Moissl-Fraund, R., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., Zitzmann, S., Höfner, S., Vincent, J. -B, Blum, J., Davidsson, Björn J. R., Sierks, H., El-Maarry, M. R., Deller, J., Hofmann, M., Hu, X., Pajola, M., Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Rickman, H., Keller, H. U., A'Hearn, M. F., Auger, A. -T, Barucci, M. A., Bertaux, J.-L, Bertini, I., Bodewits, D., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Gicquel, A., Groussin, O., Gutiérrez, P. J., Gutiérrez-Marqués, P., Güttler, C., Hviid, S. F., Ip, W.-H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kührt, E., Küppers, M., La Forgia, F., Lazzarin, M., Lopez-Moreno, J. J., Marzari, F., Michalik, H., Moissl-Fraund, R., Moreno, F., Mottola, S., Naletto, G., Oklay, N., Preusker, F., Scholten, F., Shi, X., Thomas, N., Toth, I., Tubiana, C., and Zitzmann, S.
Abstract: Context. The camera OSIRIS on board Rosetta obtained high-resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko (67P). Great parts of the nucleus surface are composed of fractured terrain. Aims. Fracture formation, evolution, and their potential relationship to physical processes that drive activity are not yet fully understood. Observed temperatures and gas production rates can be explained or interpreted with the presence of fractures by applying appropriate modelling methods. Methods. We followed a transient thermophysical model approach that includes radiative, conductive, and water-ice sublimation fluxes by considering a variety of heliocentric distances, illumination conditions, and thermophysical properties for a set of characteristic fracture geometries on the nucleus of 67P. We computed diurnal temperatures, heat fluxes, and outgassing behaviour in order to derive and distinguish the influence of the mentioned parameters on fractured terrain. Results. Our analysis confirms that fractures, as already indicated by former studies about concavities, deviate from flat-terrain topographies with equivalent properties, mostly through the effect of self-heating. Compared to flat terrain, illuminated cometary fractures are generally warmer, with smaller diurnal temperature fluctuations. Maximum sublimation rates reach higher peaks, and dust mantle quenching effects on sublimation rates are weaker. Consequently, the rough structure of the fractured terrain leads to significantly higher inferred surface thermal inertia values than for flat areas with identical physical properties, which might explain the range of measured thermal inertia on 67P. Conclusions. At 3.5 AU heliocentric distance, sublimation heat sinks in fractures converge to maximum values >50 W / m2 and trigger dust activity that can be related mainly to H2O. Fractures are likely to grow through the erosive interplay of alternating sublimation and thermal fatigue.
Published: 2017
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25. 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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26. 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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27. The pristine interior of comet 67P revealed by the combined Aswan outburst and cliff collapse

Author: Pajola, M., Hoefner, S., Vincent, J. B., Oklay, N., Scholten, F., Preusker, F., Mottola, S., Naletto, G., Fornasier, S., Lowry, S., Feller, C., Hasselmann, P. H., Guettler, C., Tubiana, C., 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., Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., El-Maarry, M. R., Ferrari, S., Ferri, F., Fulle, M., Groussin, O., Gutierrez, P., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. R., Kuehrt, E., Kuppers, M., Lara, L. M., Lin, Z. -Y, Lazzarin, M., Lucchetti, A., Moreno, J. J. Lopez, Marzari, F., Massironi, M., Michalik, H., Penasa, L., Pommerol, A., Simioni, E., Thomas, N., Toth, I., Baratti, E., Pajola, M., Hoefner, S., Vincent, J. B., Oklay, N., Scholten, F., Preusker, F., Mottola, S., Naletto, G., Fornasier, S., Lowry, S., Feller, C., Hasselmann, P. H., Guettler, C., Tubiana, C., 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., Besse, S., Boudreault, S., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Deller, J., Deshapriya, J. D. P., El-Maarry, M. R., Ferrari, S., Ferri, F., Fulle, M., Groussin, O., Gutierrez, P., Hofmann, M., Hviid, S. F., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. R., Kuehrt, E., Kuppers, M., Lara, L. M., Lin, Z. -Y, Lazzarin, M., Lucchetti, A., Moreno, J. J. Lopez, Marzari, F., Massironi, M., Michalik, H., Penasa, L., Pommerol, A., Simioni, E., Thomas, N., Toth, I., and Baratti, E.
Abstract: Outbursts occur commonly on comets(1) with different frequencies and scales(2,3). Despite multiple observations suggesting various triggering processes(4,5), the driving mechanism of such outbursts is still poorly understood. Landslides have been invoked(6) to explain some outbursts on comet 103P/Hartley (2), although the process required a pre-existing dust layer on the verge of failure. The Rosetta mission observed several outbursts from its target comet 67P/ChuryumovGerasimenko, which were attributed to dust generated by the crumbling of materials from collapsing cliffs(7,8). However, none of the aforementioned works included definitive evidence that landslides occur on comets. Amongst the many features observed by Rosetta on the nucleus of the comet, one peculiar fracture, 70 m long and 1 m wide, was identified on images obtained in September 2014 at the edge of a cliff named Aswan(9). On 10 July 2015, the Rosetta Navigation Camera captured a large plume of dust that could be traced back to an area encompassing the Aswan escarpment(7). Five days later, the OSIRIS camera observed a fresh, sharp and bright edge on the Aswan cliff. Here we report the first unambiguous link between an outburst and a cliff collapse on a comet. We establish a new dust-plume formation mechanism that does not necessarily require the breakup of pressurized crust or the presence of supervolatile material, as suggested by previous studies(7). Moreover, the collapse revealed the fresh icy interior of the comet, which is characterized by an albedo > 0.4, and provided the opportunity to study how the crumbling wall settled down to form a new talus.
Published: 2017
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28. 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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29. 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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30. 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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31. 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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32. 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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33. 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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34. 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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35. 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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36. 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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37. 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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38. The primordial nucleus of comet 67P/Churyumov-Gerasimenko

Author: Davidsson, Björn, Sierks, H., Guettler, C., Marzari, F., Pajola, M., Rickman, Hans, A'Hearn, M. F., Auger, A. -T, El-Maarry, M. R., Fornasier, S., Gutierrez, P. J., Keller, H. U., Massironi, M., Snodgrass, C., Vincent, J. -B, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Feller, C., Fulle, M., Groussin, O., Hviid, S. F., Hoefner, S., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., La Forgia, F., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Moissl-Fraund, R., Mottola, S., Naletto, G., Oklay, N., Thomas, N., Tubiana, C., Davidsson, Björn, Sierks, H., Guettler, C., Marzari, F., Pajola, M., Rickman, Hans, A'Hearn, M. F., Auger, A. -T, El-Maarry, M. R., Fornasier, S., Gutierrez, P. J., Keller, H. U., Massironi, M., Snodgrass, C., Vincent, J. -B, Barbieri, C., Lamy, P. L., Rodrigo, R., Koschny, D., Barucci, M. A., Bertaux, J. -L, Bertini, I., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Feller, C., Fulle, M., Groussin, O., Hviid, S. F., Hoefner, S., Ip, W. -H, Jorda, L., Knollenberg, J., Kovacs, G., Kramm, J. -R, Kuehrt, E., Kueppers, M., La Forgia, F., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Moissl-Fraund, R., Mottola, S., Naletto, G., Oklay, N., Thomas, N., and Tubiana, C.
Abstract: Context. We investigate the formation and evolution of comet nuclei and other trans-Neptunian objects (TNOs) in the solar nebula and primordial disk prior to the giant planet orbit instability foreseen by the Nice model. Aims. Our goal is to determine whether most observed comet nuclei are primordial rubble-pile survivors that formed in the solar nebula and young primordial disk or collisional rubble piles formed later in the aftermath of catastrophic disruptions of larger parent bodies. We also propose a concurrent comet and TNO formation scenario that is consistent with observations. Methods. We used observations of comet 67P/Churyumov-Gerasimenko by the ESA Rosetta spacecraft, particularly by the OSIRIS camera system, combined with data from the NASA Stardust sample-return mission to comet 81P/Wild 2 and from meteoritics; we also used existing observations from ground or from spacecraft of irregular satellites of the giant planets, Centaurs, and TNOs. We performed modeling of thermophysics, hydrostatics, orbit evolution, and collision physics. Results. We find that thermal processing due to short-lived radionuclides, combined with collisional processing during accretion in the primordial disk, creates a population of medium-sized bodies that are comparably dense, compacted, strong, heavily depleted in supervolatiles like CO and CO2; they contain little to no amorphous water ice, and have experienced extensive metasomatism and aqueous alteration due to liquid water. Irregular satellites Phoebe and Himalia are potential representatives of this population. Collisional rubble piles inherit these properties from their parents. Contrarily, comet nuclei have low density, high porosity, weak strength, are rich in supervolatiles, may contain amorphous water ice, and do not display convincing evidence of in situ metasomatism or aqueous alteration. We outline a comet formation scenario that starts in the solar nebula and ends in the primordial disk, that reproduces these ob
Published: 2016
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39. 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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40. 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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41. 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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42. 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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43. 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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44. The Agilkia boulders/pebbles size-frequency distributions : OSIRIS and ROLIS joint observations of 67P surface

Author: Pajola, M., Mottola, S., Hamm, M., Fulle, M., Davidsson, B., Guettler, C., Sierks, H., Naletto, G., Arnold, G., Grothues, H. -G, Jaumann, R., Michaelis, H., Bibring, J. P., 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., Boudreault, S., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., El Maarry, M. R., Feller, C., Fornasier, S., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. H., Jorda, L., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., La Forgia, F., Lara, L. M., Lin, Z. Y., Lazzarin, M., Moreno, J. J. Lopez, Lucchetti, A., Marzari, F., Massironi, M., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Thomas, N., Tubiana, C., Vincent, J. B., Pajola, M., Mottola, S., Hamm, M., Fulle, M., Davidsson, B., Guettler, C., Sierks, H., Naletto, G., Arnold, G., Grothues, H. -G, Jaumann, R., Michaelis, H., Bibring, J. P., 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., Boudreault, S., Cremonese, G., Da Deppo, V., Debei, S., De Cecco, M., Deller, J., El Maarry, M. R., Feller, C., Fornasier, S., Gicquel, A., Groussin, O., Gutierrez, P. J., Hofmann, M., Hviid, S. F., Ip, W. H., Jorda, L., Knollenberg, J., Kramm, J. R., Kuehrt, E., Kuppers, M., La Forgia, F., Lara, L. M., Lin, Z. Y., Lazzarin, M., Moreno, J. J. Lopez, Lucchetti, A., Marzari, F., Massironi, M., Michalik, H., Oklay, N., Pommerol, A., Preusker, F., Scholten, F., Thomas, N., Tubiana, C., and Vincent, J. B.
Abstract: By using the images acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) and ROLIS (ROsetta Lander Imaging System) cameras, we derive the size-frequency distribution (SFD) of cometary pebbles and boulders covering the size range 0.05-30.0 m on the Agilkia landing site. The global SFD measured on OSIRIS images, reflects the different properties of the multiple morphological units present on Agilkia, combined with selection effects related to lifting, transport and redeposition. Contrarily, the different ROLIS SFD derived on the smooth and rough units may be related to their different regolith thickness present on Agilkia. In the thicker, smoother layer, ROLIS mainly measures the SFD of the airfall population which almost completely obliterates the signature of underlying boulders up to a size of the order of 1 m. This is well matched by the power-law index derived analysing coma particles identified by the grain analyser Grain Impact Analyser and Dust Accumulator. This result confirms the important blanketing dynamism of Agilkia. The steeper SFD observed in rough terrains from 0.4 to 2 m could point out intrinsic differences between northern and southern dust size distributions, or it may suggest that the underlying boulders 'peek through' the thinner airfall layer in the rough terrain, thereby producing the observed excess in the decimetre size range. Eventually, the OSIRIS SFD performed on the Philae landing unit may be due to water sublimation from a static population of boulders, affecting smaller boulders before the bigger ones, thus shallowing the original SFD.
Published: 2016
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45. 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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46. 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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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. 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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49. 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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50. A mini outburst from the nightside of comet 67P/Churyumov-Gerasimenko observed by the OSIRIS camera on Rosetta

Author: Knollenberg, J., Lin, Z. Y., Hviid, S. F., Oklay, N., Vincent, J. -B, Bodewits, D., Mottola, S., Pajola, M., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bertaux, J. L., Bertini, I., Cremonese, G., Davidsson, Björn, Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Ip, W. -H, Jorda, L., Keller, H. U., Kuehrt, E., Kramm, J. R., Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Thomas, N., Guettler, C., Preusker, F., Scholten, F., Tubiana, C., Knollenberg, J., Lin, Z. Y., Hviid, S. F., Oklay, N., Vincent, J. -B, Bodewits, D., Mottola, S., Pajola, M., Sierks, H., Barbieri, C., Lamy, P., Rodrigo, R., Koschny, D., Rickman, Hans, A'Hearn, M. F., Barucci, M. A., Bertaux, J. L., Bertini, I., Cremonese, G., Davidsson, Björn, Da Deppo, V., Debei, S., De Cecco, M., Fornasier, S., Fulle, M., Groussin, O., Gutierrez, P. J., Ip, W. -H, Jorda, L., Keller, H. U., Kuehrt, E., Kramm, J. R., Kuppers, M., Lara, L. M., Lazzarin, M., Moreno, J. J. Lopez, Marzari, F., Naletto, G., Thomas, N., Guettler, C., Preusker, F., Scholten, F., and Tubiana, C.
Abstract: Context. On 12 March 2015 the OSIRIS WAC camera onboard the ESA Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko observed a small outburst originating from the Imhotep region at the foot of the big lobe of the comet. These measurements are unique since it was the first time that the initial phase of a transient outburst event could be directly observed. Aims. We investigate the evolution of the dust jet in order to derive clues about the outburst source mechanism and the ejected dust particles, in particular the dust mass, dust-to-gas ratio and the particle size distribution. Methods. Analysis of the images and of the observation geometry using comet shape models in combination with gasdynamic modeling of the transient dust jet were the main tools used in this study. Synthetic images were computed for comparison with the observations. Results. Analysis of the geometry revealed that the source region was not illuminated until 1.5 h after the event implying true nightside activity was observed. The outburst lasted for less than one hour and the average dust production rate during the initial four minutes was of the order of 1 kg/s. During this time the outburst dust production rate was approximately constant, no sign for an initial explosion could be detected. For dust grains between 0.01-1 mm a power law size distribution characterized by an index of about 2.6 provides the best fit to the observed radiance profiles. The dust-to-gas ratio of the outburst jet is in the range 0.6-1.8.
Published: 2016
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