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1. The tides of Enceladus' porous core

Author: Rovira-Navarro, M., Katz, R.F., Liao, Y., van der Wal, W., Nimmo, F., Rovira-Navarro, M., Katz, R.F., Liao, Y., van der Wal, W., and Nimmo, F.
Abstract: The inferred density of Enceladus' core, together with evidence of hydrothermal activity within the moon, suggests that the core is porous. Tidal dissipation in an unconsolidated core has been proposed as the main source of Enceladus' geological activity. However, the tidal response of its core has generally been modeled assuming it behaves viscoelastically rather than poroviscoelastically. In this work, we analyze the poroviscoelastic response to better constrain the distribution of tidal dissipation within Enceladus. A poroviscoelastic body has a different tidal response than a viscoelastic one; pressure within the pores alters the stress field and induces a Darcian porous flow. This flow represents an additional pathway for energy dissipation. Using Biot's theory of poroviscoelasticity, we develop a new framework to obtain the tidal response of a spherically symmetric, self-gravitating moon with porous layers and apply it to Enceladus. We show that the boundary conditions at the interface of the core and overlying ocean play a key role in the tidal response. The ocean hinders the development of a large-amplitude Darcian flow, making negligible the Darcian contribution to the dissipation budget. We therefore infer that Enceladus' core can be the source of its geological activity only if it has a low rigidity and a very low viscosity. A future mission to Enceladus could test this hypothesis by measuring the phase lags of tidally induced changes of gravitational potential and surface displacements.
Published: 2022

2. InSight Constraints on the Global Character of the Martian Crust

Author: Wieczorek, MA, Wieczorek, MA, Broquet, A, McLennan, SM, Rivoldini, A, Golombek, M, Antonangeli, D, Beghein, C, Giardini, D, Gudkova, T, Gyalay, S, Johnson, CL, Joshi, R, Kim, D, King, SD, Knapmeyer-Endrun, B, Lognonné, P, Michaut, C, Mittelholz, A, Nimmo, F, Ojha, L, Panning, MP, Plesa, AC, Siegler, MA, Smrekar, SE, Spohn, T, Banerdt, WB, Wieczorek, MA, Wieczorek, MA, Broquet, A, McLennan, SM, Rivoldini, A, Golombek, M, Antonangeli, D, Beghein, C, Giardini, D, Gudkova, T, Gyalay, S, Johnson, CL, Joshi, R, Kim, D, King, SD, Knapmeyer-Endrun, B, Lognonné, P, Michaut, C, Mittelholz, A, Nimmo, F, Ojha, L, Panning, MP, Plesa, AC, Siegler, MA, Smrekar, SE, Spohn, T, and Banerdt, WB
Abstract: Analyses of seismic data from the InSight mission have provided the first in situ constraints on the thickness of the crust of Mars. These crustal thickness constraints are currently limited to beneath the lander that is located in the northern lowlands, and we use gravity and topography data to construct global crustal thickness models that satisfy the seismic data. These models consider a range of possible mantle and core density profiles, a range of crustal densities, a low-density surface layer, and the possibility that the crustal density of the northern lowlands is greater than that of the southern highlands. Using the preferred InSight three-layer seismic model of the crust, the average crustal thickness of the planet is found to lie between 30 and 72 km. Depending on the choice of the upper mantle density, the maximum permissible density of the northern lowlands and southern highlands crust is constrained to be between 2,850 and 3,100 kg m−3. These crustal densities are lower than typical Martian basaltic materials and are consistent with a crust that is on average more felsic than the materials found at the surface. We argue that a substantial portion of the crust of Mars is a primary crust that formed during the initial differentiation of the planet. Various hypotheses for the origin of the observed intracrustal seisimic layers are assessed, with our preferred interpretation including thick volcanic deposits, ejecta from the Utopia basin, porosity closure, and differentiation products of a Borealis impact melt sheet.
Published: 2022

3. Surface waves and crustal structure on Mars.

Author: Kim, D, Kim, D, Banerdt, WB, Ceylan, S, Giardini, D, Lekić, V, Lognonné, P, Beghein, C, Beucler, É, Carrasco, S, Charalambous, C, Clinton, J, Drilleau, M, Durán, C, Golombek, M, Joshi, R, Khan, A, Knapmeyer-Endrun, B, Li, J, Maguire, R, Pike, WT, Samuel, H, Schimmel, M, Schmerr, NC, Stähler, SC, Stutzmann, E, Wieczorek, M, Xu, Z, Batov, A, Bozdag, E, Dahmen, N, Davis, P, Gudkova, T, Horleston, A, Huang, Q, Kawamura, T, King, SD, McLennan, SM, Nimmo, F, Plasman, M, Plesa, AC, Stepanova, IE, Weidner, E, Zenhäusern, G, Daubar, IJ, Fernando, B, Garcia, RF, Posiolova, LV, Panning, MP, Kim, D, Kim, D, Banerdt, WB, Ceylan, S, Giardini, D, Lekić, V, Lognonné, P, Beghein, C, Beucler, É, Carrasco, S, Charalambous, C, Clinton, J, Drilleau, M, Durán, C, Golombek, M, Joshi, R, Khan, A, Knapmeyer-Endrun, B, Li, J, Maguire, R, Pike, WT, Samuel, H, Schimmel, M, Schmerr, NC, Stähler, SC, Stutzmann, E, Wieczorek, M, Xu, Z, Batov, A, Bozdag, E, Dahmen, N, Davis, P, Gudkova, T, Horleston, A, Huang, Q, Kawamura, T, King, SD, McLennan, SM, Nimmo, F, Plasman, M, Plesa, AC, Stepanova, IE, Weidner, E, Zenhäusern, G, Daubar, IJ, Fernando, B, Garcia, RF, Posiolova, LV, and Panning, MP
Abstract: We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.
Published: 2022

4. The tides of Enceladus' porous core

Author: Rovira-Navarro, M., Katz, R.F., Liao, Y., van der Wal, W., Nimmo, F., Rovira-Navarro, M., Katz, R.F., Liao, Y., van der Wal, W., and Nimmo, F.
Abstract: The inferred density of Enceladus' core, together with evidence of hydrothermal activity within the moon, suggests that the core is porous. Tidal dissipation in an unconsolidated core has been proposed as the main source of Enceladus' geological activity. However, the tidal response of its core has generally been modeled assuming it behaves viscoelastically rather than poroviscoelastically. In this work, we analyze the poroviscoelastic response to better constrain the distribution of tidal dissipation within Enceladus. A poroviscoelastic body has a different tidal response than a viscoelastic one; pressure within the pores alters the stress field and induces a Darcian porous flow. This flow represents an additional pathway for energy dissipation. Using Biot's theory of poroviscoelasticity, we develop a new framework to obtain the tidal response of a spherically symmetric, self-gravitating moon with porous layers and apply it to Enceladus. We show that the boundary conditions at the interface of the core and overlying ocean play a key role in the tidal response. The ocean hinders the development of a large-amplitude Darcian flow, making negligible the Darcian contribution to the dissipation budget. We therefore infer that Enceladus' core can be the source of its geological activity only if it has a low rigidity and a very low viscosity. A future mission to Enceladus could test this hypothesis by measuring the phase lags of tidally induced changes of gravitational potential and surface displacements.
Published: 2022

5. Surface waves and crustal structure on Mars

Author: Kim, D., Banerdt, W. B., Ceylan, S., Giardini, D., Lekic, V., Lognonne, P., Beghein, C., Beucler, E., Carrasco, S., Charalambous, C., Clinton, J., Drilleau, M., Duran, C., Golombek, M., Joshi, R., Khan, A., Knapmeyer-Endrun, B., Li, J., Maguire, R., Pike, W. T., Samuel, H., Schimmel, M., Schmerr, N. C., Stahler, S. C., Stutzmann, E., Wieczorek, M., Xu, Z., Batov, A., Bozdag, E., Dahmen, N., Davis, P., Gudkova, T., Horleston, A., Huang, Q., Kawamura, T., King, Scott D., McLennan, S. M., Nimmo, F., Plasman, M., Plesa, A. C., Stepanova, I. E., Weidner, E., Zenhausern, G., Daubar, I. J., Fernando, B., Garcia, R. F., Posiolova, L., Panning, M. P., Kim, D., Banerdt, W. B., Ceylan, S., Giardini, D., Lekic, V., Lognonne, P., Beghein, C., Beucler, E., Carrasco, S., Charalambous, C., Clinton, J., Drilleau, M., Duran, C., Golombek, M., Joshi, R., Khan, A., Knapmeyer-Endrun, B., Li, J., Maguire, R., Pike, W. T., Samuel, H., Schimmel, M., Schmerr, N. C., Stahler, S. C., Stutzmann, E., Wieczorek, M., Xu, Z., Batov, A., Bozdag, E., Dahmen, N., Davis, P., Gudkova, T., Horleston, A., Huang, Q., Kawamura, T., King, Scott D., McLennan, S. M., Nimmo, F., Plasman, M., Plesa, A. C., Stepanova, I. E., Weidner, E., Zenhausern, G., Daubar, I. J., Fernando, B., Garcia, R. F., Posiolova, L., and Panning, M. P.
Abstract: We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.
Published: 2022

6. Surface waves and crustal structure on Mars

Author: Kim, D., Banerdt, W. B., Ceylan, S., Giardini, D., Lekic, V, Lognonne, P., Beghein, C., Beucler, E., Carrasco, S., Charalambous, C., Clinton, J., Drilleau, M., Duran, C., Golombek, M., Joshi, R., Khan, A., Knapmeyer-Endrun, B., Li, J., Maguire, R., Pike, W. T., Samuel, H., Schimmel, M., Schmerr, N. C., Stahler, S. C., Stutzmann, E., Wieczorek, M., Xu, Z., Batov, A., Bozdag, E., Dahmen, N., Davis, P., Gudkova, T., Horleston, A., Huang, Q., Kawamura, T., King, S. D., McLennan, S. M., Nimmo, F., Plasman, M., Plesa, A. C., Stepanova, I. E., Weidner, E., Zenhausern, G., Daubar, I. J., Fernando, B., Garcia, R. F., Posiolova, L., V, Panning, M. P., Kim, D., Banerdt, W. B., Ceylan, S., Giardini, D., Lekic, V, Lognonne, P., Beghein, C., Beucler, E., Carrasco, S., Charalambous, C., Clinton, J., Drilleau, M., Duran, C., Golombek, M., Joshi, R., Khan, A., Knapmeyer-Endrun, B., Li, J., Maguire, R., Pike, W. T., Samuel, H., Schimmel, M., Schmerr, N. C., Stahler, S. C., Stutzmann, E., Wieczorek, M., Xu, Z., Batov, A., Bozdag, E., Dahmen, N., Davis, P., Gudkova, T., Horleston, A., Huang, Q., Kawamura, T., King, S. D., McLennan, S. M., Nimmo, F., Plasman, M., Plesa, A. C., Stepanova, I. E., Weidner, E., Zenhausern, G., Daubar, I. J., Fernando, B., Garcia, R. F., Posiolova, L., V, and Panning, M. P.
Published: 2022

7. Surface waves and crustal structure on Mars

Author: ETH Zurich, NASA Astrobiology Institute (US), Agence Nationale de la Recherche (France), UK Space Agency, California Institute of Technology, National Aeronautics and Space Administration (US), Kim, D., Banerdt, W. B., Ceylan, S., Giardini, Domenico, Lekic, Vedran, Lognonné, P., Beghein, C., Beucler, E., Carrasco, Sebastián, Charalambous, C., Clinton, John F., Drilleau, M., Duran, C., Golombek, M. P., Joshi, R., Khan, A., Knapmeyer‐Endrun, Brigitte, Li, J., Maguire, R., Pike, William T., Samuel, H., Schimmel, Martin, Schmerr, Nicholas C., Stähler, S. C., Stutzmann, E., Wieczorek, M., Xu, Z. D., Batov, A., Bozdag, E., Dahmen, N., Davis, P., Gudkova, T., Horleston, A., Huang, Quancheng, Kawamura, T., King, S., McLennan, S M, Nimmo, F., Plasman, M., Plesa, A. C., Stepanova, I. E., Weidner, E., Zenhäusern, Geraldine, Daubar, I., Fernando, B., García, R. F., Posiolova, L. V., Panning, Mark P., ETH Zurich, NASA Astrobiology Institute (US), Agence Nationale de la Recherche (France), UK Space Agency, California Institute of Technology, National Aeronautics and Space Administration (US), Kim, D., Banerdt, W. B., Ceylan, S., Giardini, Domenico, Lekic, Vedran, Lognonné, P., Beghein, C., Beucler, E., Carrasco, Sebastián, Charalambous, C., Clinton, John F., Drilleau, M., Duran, C., Golombek, M. P., Joshi, R., Khan, A., Knapmeyer‐Endrun, Brigitte, Li, J., Maguire, R., Pike, William T., Samuel, H., Schimmel, Martin, Schmerr, Nicholas C., Stähler, S. C., Stutzmann, E., Wieczorek, M., Xu, Z. D., Batov, A., Bozdag, E., Dahmen, N., Davis, P., Gudkova, T., Horleston, A., Huang, Quancheng, Kawamura, T., King, S., McLennan, S M, Nimmo, F., Plasman, M., Plesa, A. C., Stepanova, I. E., Weidner, E., Zenhäusern, Geraldine, Daubar, I., Fernando, B., García, R. F., Posiolova, L. V., and Panning, Mark P.
Abstract: We detected surface waves from two meteorite impacts on Mars. By measuring group velocity dispersion along the impact-lander path, we obtained a direct constraint on crustal structure away from the InSight lander. The crust north of the equatorial dichotomy had a shear wave velocity of approximately 3.2 kilometers per second in the 5- to 30-kilometer depth range, with little depth variation. This implies a higher crustal density than inferred beneath the lander, suggesting either compositional differences or reduced porosity in the volcanic areas traversed by the surface waves. The lower velocities and the crustal layering observed beneath the landing site down to a 10-kilometer depth are not a global feature. Structural variations revealed by surface waves hold implications for models of the formation and thickness of the martian crust.
Published: 2022

8. Enceladus as a potential oasis for life:science goals and investigations for future explorations

Author: Choblet, G. (Gaël), Tobie, G. (Gabriel), Buch, A. (Arnaud), Čadek, O. (Ondrej), Barge, L. M. (Laura M.), Bēhounková, M. (Marie), Camprubi, E. (Eloi), Freissinet, C. (Caroline), Hedman, M. (Matt), Jones, G. (Geraint), Lainey, V. (Valery), Le Gall, A. (Alice), Lucchetti, A. (Alice), MacKenzie, S. (Shannon), Mitri, G. (Giuseppe), Neveu, M. (Marc), Nimmo, F. (Francis), Olsson-Francis, K. (Karen), Panning, M. (Mark), Postberg, F. (Frank), Saur, J. (Joachim), Schmidt, J. (Jürgen), Sekine, Y. (Yasuhito), Shibuya, T. (Takazo), Sotin, C. (Christophe), Soucek, O. (Ondrej), Szopa, C. (Cyril), Usui, T. (Tomohiro), Vance, S. (Steven), Van Hoolst, T. (Tim), Choblet, G. (Gaël), Tobie, G. (Gabriel), Buch, A. (Arnaud), Čadek, O. (Ondrej), Barge, L. M. (Laura M.), Bēhounková, M. (Marie), Camprubi, E. (Eloi), Freissinet, C. (Caroline), Hedman, M. (Matt), Jones, G. (Geraint), Lainey, V. (Valery), Le Gall, A. (Alice), Lucchetti, A. (Alice), MacKenzie, S. (Shannon), Mitri, G. (Giuseppe), Neveu, M. (Marc), Nimmo, F. (Francis), Olsson-Francis, K. (Karen), Panning, M. (Mark), Postberg, F. (Frank), Saur, J. (Joachim), Schmidt, J. (Jürgen), Sekine, Y. (Yasuhito), Shibuya, T. (Takazo), Sotin, C. (Christophe), Soucek, O. (Ondrej), Szopa, C. (Cyril), Usui, T. (Tomohiro), Vance, S. (Steven), and Van Hoolst, T. (Tim)
Abstract: Enceladus is the first planetary object for which direct sampling of a subsurface water reservoir, likely habitable, has been performed. Over a decade of flybys and seven flythroughs of its watery plume, the Cassini spacecraft determined that Enceladus possesses all the ingredients for life. The existence of active eruptions blasting fresh water into space, makes Enceladus the easiest target in the search for life elsewhere in the Solar System. Flying again through the plume with more advanced instruments, landing at the surface near active sources and collecting a sample for return to Earth are the natural next steps for assessing whether life emerges in this active world. Characterizing this habitable world also requires detailed mapping and monitoring of its tidally-induced activity, from the orbit as well as from the surface using complementary platforms. Such ambitious goals may be achieved in the future in the framework of ESA large or medium-class missions in partnership with other international agencies, in the same spirit of the successful Cassini-Huygens mission. For all these reasons, exploring habitable ocean worlds, with Enceladus as a primary target, should be a priority topic of the ESA Voyage 2050 programme.
Published: 2021

9. Potential Pitfalls in the Analysis and Structural Interpretation of Seismic Data from the Mars InSight Mission.

Author: Kim, D, Kim, D, Davis, P, Lekić, V, Maguire, R, Compaire, N, Schimmel, M, Stutzmann, E, Irving, JCE, Lognonné, P, Scholz, J-R, Clinton, J, Zenhäusern, G, Dahmen, N, Deng, S, Levander, A, Panning, MP, Garcia, RF, Giardini, D, Hurst, K, Knapmeyer-Endrun, B, Nimmo, F, Pike, WT, Pou, L, Schmerr, N, Stähler, SC, Tauzin, B, Widmer-Schnidrig, R, Banerdt, WB, Kim, D, Kim, D, Davis, P, Lekić, V, Maguire, R, Compaire, N, Schimmel, M, Stutzmann, E, Irving, JCE, Lognonné, P, Scholz, J-R, Clinton, J, Zenhäusern, G, Dahmen, N, Deng, S, Levander, A, Panning, MP, Garcia, RF, Giardini, D, Hurst, K, Knapmeyer-Endrun, B, Nimmo, F, Pike, WT, Pou, L, Schmerr, N, Stähler, SC, Tauzin, B, Widmer-Schnidrig, R, and Banerdt, WB
Abstract: The Seismic Experiment for Interior Structure (SEIS) of the InSight mission to Mars, has been providing direct information on Martian interior structure and dynamics of that planet since it landed. Compared to seismic recordings on Earth, ground motion measurements acquired by SEIS on Mars are made under dramatically different ambient noise conditions, but include idiosyncratic signals that arise from coupling between different InSight sensors and spacecraft components. This work is to synthesize what is known about these signal types, illustrate how they can manifest in waveforms and noise correlations, and present pitfalls in structural interpretations based on standard seismic analysis methods. We show that glitches, a type of prominent transient signal, can produce artifacts in ambient noise correlations. Sustained signals that vary in frequency, such as lander modes which are affected by variations in temperature and wind conditions over the course of the Martian Sol, can also contaminate ambient noise results. Therefore, both types of signals have the potential to bias interpretation in terms of subsurface layering. We illustrate that signal processing in the presence of identified nonseismic signals must be informed by an understanding of the underlying physical processes in order for high fidelity waveforms of ground motion to be extracted. While the origins of most idiosyncratic signals are well understood, the 2.4 Hz resonance remains debated and the literature does not contain an explanation of its fine spectral structure. Even though the selection of idiosyncratic signal types discussed in this paper may not be exhaustive, we provide guidance on best practices for enhancing the robustness of structural interpretations.
Published: 2021

10. Seismic detection of the martian core by InSight

Author: Schimmel, Martin, Stähler, S. C., Savas, Ceylan, Duran, A. C., García, Raphael, Giardini, Domenico, Huang, Quancheng, Khan, A., Kim, Doyeon, Lognonné, P., Maguire, Ross, Marusiak, A. G., Plesa, A. C., Samuel, Henri, Schmerr, Nicholas C., Sollberger, David, Stutzmann, E., Antonangeli, D., Clinton, John F., van Driel, M., Drilleau, M., Gudkova, T., Horleston, Anna, Irving, J., Kawamura, T., Lekic, Vedran, Myhill, Robert, Nimmo, F., Panning, Mark, Rivoldini, A., Schmelzbach, C., Stanley, S., Weber, R., Xu, Zongbo, Zenhäusern, G., Banerdt, W. B., Schimmel, Martin, Stähler, S. C., Savas, Ceylan, Duran, A. C., García, Raphael, Giardini, Domenico, Huang, Quancheng, Khan, A., Kim, Doyeon, Lognonné, P., Maguire, Ross, Marusiak, A. G., Plesa, A. C., Samuel, Henri, Schmerr, Nicholas C., Sollberger, David, Stutzmann, E., Antonangeli, D., Clinton, John F., van Driel, M., Drilleau, M., Gudkova, T., Horleston, Anna, Irving, J., Kawamura, T., Lekic, Vedran, Myhill, Robert, Nimmo, F., Panning, Mark, Rivoldini, A., Schmelzbach, C., Stanley, S., Weber, R., Xu, Zongbo, Zenhäusern, G., and Banerdt, W. B.
Abstract: A plethora of geophysical, geo- chemical, and geodynamical observations indicate that the terrestrial planets have differentiated into silicate crusts and mantles that surround a dense core. The latter consists primarily of Fe and some lighter alloying elements (e.g., S, Si, C, O, and H) [1]¿. The Martian meteorites show evidence of chalcophile element depletion, suggesting that the otherwise Fe-Ni- rich core likely contains a sulfide component, which influences physical state.
Published: 2021

11. Potential Pitfalls in the Analysis and Structural Interpretation of Seismic Data from the Mars InSight Mission

Author: German Centre for Air and Space Travel, David and Lucile Packard Foundation, California Institute of Technology, Ministerio de Ciencia, Innovación y Universidades (España), Generalitat de Catalunya, European Commission, Agence Nationale de la Recherche (France), Schimmel, Martin [0000-0003-2601-4462], Kim, Doyeon, Davis, Paul, Lekic, Vedran, Maguire, Ross, Compaire, Nicolas, Schimmel, Martin, Stutzmann, E., Irving, Jessica C. E., Lognonné, P., Scholz, J. R., Clinton, John F., Zenhäusern, G., Deng, Sizhuang, Levander, A., Panning, Mark P., Garcia, Raphael F., Giardini, Domenico, Hurst, K., Knapmeyer‐Endrun, Brigitte, Nimmo, F., Pike, William T., Pou, Laurent, Schmerr, N., Stahler, S. C., Tauzin, Benoit, Widmer‐Schnidrig, Rudolf, Banerdt, William B., German Centre for Air and Space Travel, David and Lucile Packard Foundation, California Institute of Technology, Ministerio de Ciencia, Innovación y Universidades (España), Generalitat de Catalunya, European Commission, Agence Nationale de la Recherche (France), Schimmel, Martin [0000-0003-2601-4462], Kim, Doyeon, Davis, Paul, Lekic, Vedran, Maguire, Ross, Compaire, Nicolas, Schimmel, Martin, Stutzmann, E., Irving, Jessica C. E., Lognonné, P., Scholz, J. R., Clinton, John F., Zenhäusern, G., Deng, Sizhuang, Levander, A., Panning, Mark P., Garcia, Raphael F., Giardini, Domenico, Hurst, K., Knapmeyer‐Endrun, Brigitte, Nimmo, F., Pike, William T., Pou, Laurent, Schmerr, N., Stahler, S. C., Tauzin, Benoit, Widmer‐Schnidrig, Rudolf, and Banerdt, William B.
Abstract: The Seismic Experiment for Interior Structure (SEIS) of the InSight mission to Mars has been providing direct information on Martian interior structure and dynamics of that planet since it landed. Compared with seismic recordings on the Earth, ground‐motion measurements acquired by SEIS on Mars are not only made under dramatically different ambient noise conditions, but also include idiosyncratic signals that arise from coupling between different InSight sensors and spacecraft components. This work is to synthesize what is known about these signal types, illustrate how they can manifest in waveforms and noise correlations, and present pitfalls in structural interpretations based on standard seismic analysis methods. We show that glitches (a type of prominent transient signal) can produce artifacts in ambient noise correlations. Sustained signals that vary in frequency, such as lander modes that are affected by variations in temperature and wind conditions over the course of the Martian sol, can also contaminate ambient noise results. Therefore, both types of signals have the potential to bias interpretation in terms of subsurface layering. We illustrate that signal processing in the presence of identified nonseismic signals must be informed by an understanding of the underlying physical processes in order for high‐fidelity waveforms of ground motion to be extracted. Whereas the origins of the most idiosyncratic signals are well understood, the 2.4 Hz resonance remains debated, and the literature does not contain an explanation of its fine spectral structure. Even though the selection of idiosyncratic signal types discussed in this article may not be exhaustive, we provide guidance on the best practices for enhancing the robustness of structural interpretations.
Published: 2021

12. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data

Author: Lognonné, P.; Banerdt, W.B.; Pike, W.T.; Giardini, D.; Christensen, U.; Garcia, R.F.; Kawamura, T.; Kedar, S.; Knapmeyer-Endrun, B.; Margerin, L.; Nimmo, F.; Panning, M.; Tauzin, B.; Scholz, J.R.; Antonangeli, D.; Barkaoui, S.; Beucler, E.; Bissig, F.; Brinkman, N.; Calvet, M.; Ceylan, S.; Charalambous, C.; Davis, P.; van Driel, M.; Drilleau, M.; Fayon, L.; Joshi, R.; Kenda, B.; Khan, A.; Knapmeyer, M.; Lekic, V.; McClean, J.; Mimoun, D.; Murdoch, N.; Pan, L.; Perrin, C.; Pinot, B.; Pou, L.; Menina, S.; Rodriguez, S.; Schmelzbach, C.; Schmerr, N.; Sollberger, D.; Spiga, A.; Stähler, S.; Stott, A.; Stutzmann, E.; Tharimena, S.; Widmer-Schnidrig, R.; Schimmel, M.; Rodriguez Manfredi, J.A. and Lognonné, P.; Banerdt, W.B.; Pike, W.T.; Giardini, D.; Christensen, U.; Garcia, R.F.; Kawamura, T.; Kedar, S.; Knapmeyer-Endrun, B.; Margerin, L.; Nimmo, F.; Panning, M.; Tauzin, B.; Scholz, J.R.; Antonangeli, D.; Barkaoui, S.; Beucler, E.; Bissig, F.; Brinkman, N.; Calvet, M.; Ceylan, S.; Charalambous, C.; Davis, P.; van Driel, M.; Drilleau, M.; Fayon, L.; Joshi, R.; Kenda, B.; Khan, A.; Knapmeyer, M.; Lekic, V.; McClean, J.; Mimoun, D.; Murdoch, N.; Pan, L.; Perrin, C.; Pinot, B.; Pou, L.; Menina, S.; Rodriguez, S.; Schmelzbach, C.; Schmerr, N.; Sollberger, D.; Spiga, A.; Stähler, S.; Stott, A.; Stutzmann, E.; Tharimena, S.; Widmer-Schnidrig, R.; Schimmel, M.; Rodriguez Manfredi, J.A.
Abstract: Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.
Published: 2020

13. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data

Author: Lognonne, P., Banerdt, W. B., Pike, W. T., Giardini, D., Christensen, U., Garcia, R. F., Kawamura, T., Kedar, S., Knapmeyer-Endrun, B., Margerin, L., Nimmo, F., Panning, M., Tauzin, B., Scholz, J. -R., Antonangeli, D., Barkaoui, S., Beucler, E., Bissig, F., Brinkman, N., Calvet, M., Ceylan, S., Charalambous, C., Davis, P., Van Driel, M., Drilleau, M., Fayon, L., Joshi, R., Kenda, B., Khan, A., Knapmeyer, M., Lekic, V., McClean, J., Mimoun, D., Murdoch, N., Pan, L., Perrin, C., Pinot, B., Pou, L., Menina, S., Rodriguez, S., Schmelzbach, C., Schmerr, N., Sollberger, D., Spiga, A., Staehler, S., Stott, A., Stutzmann, E., Tharimena, S., Widmer-Schnidrig, R., Andersson, F., Ansan, V., Beghein, C., Boese, M., Bozdag, E., Clinton, J., Daubar, I., Delage, P., Fuji, N., Golombek, M., Grott, M., Horleston, A., Hurst, K., Irving, J., Jacob, A., Knollenberg, J., Krasner, S., Krause, C., Lorenz, R., Michaut, C., Myhill, R., Nissen-Meyer, T., Ten Pierick, J., Plesa, A. -C., Quantin-Nataf, C., Robertsson, J., Rochas, L., Schimmel, M., Smrekar, S., Spohn, T., Teanby, N., Tromp, J., Vallade, J., Verdier, N., Vrettos, C., Weber, R., Banfield, D., Barrett, E., Bierwirth, M., Calcutt, S., Compaire, N., Johnson, C. L., Mance, D., Euchner, F., Kerjean, L., Mainsant, G., Mocquet, A., Rodriguez Manfredi, J. A., Pont, G., Laudet, P., Nebut, T., De Raucourt, S., Robert, O., Russell, C. T., Sylvestre-Baron, A., Tillier, S., Warren, T., Wieczorek, M., Yana, C., Zweifel, P., Lognonne, P., Banerdt, W. B., Pike, W. T., Giardini, D., Christensen, U., Garcia, R. F., Kawamura, T., Kedar, S., Knapmeyer-Endrun, B., Margerin, L., Nimmo, F., Panning, M., Tauzin, B., Scholz, J. -R., Antonangeli, D., Barkaoui, S., Beucler, E., Bissig, F., Brinkman, N., Calvet, M., Ceylan, S., Charalambous, C., Davis, P., Van Driel, M., Drilleau, M., Fayon, L., Joshi, R., Kenda, B., Khan, A., Knapmeyer, M., Lekic, V., McClean, J., Mimoun, D., Murdoch, N., Pan, L., Perrin, C., Pinot, B., Pou, L., Menina, S., Rodriguez, S., Schmelzbach, C., Schmerr, N., Sollberger, D., Spiga, A., Staehler, S., Stott, A., Stutzmann, E., Tharimena, S., Widmer-Schnidrig, R., Andersson, F., Ansan, V., Beghein, C., Boese, M., Bozdag, E., Clinton, J., Daubar, I., Delage, P., Fuji, N., Golombek, M., Grott, M., Horleston, A., Hurst, K., Irving, J., Jacob, A., Knollenberg, J., Krasner, S., Krause, C., Lorenz, R., Michaut, C., Myhill, R., Nissen-Meyer, T., Ten Pierick, J., Plesa, A. -C., Quantin-Nataf, C., Robertsson, J., Rochas, L., Schimmel, M., Smrekar, S., Spohn, T., Teanby, N., Tromp, J., Vallade, J., Verdier, N., Vrettos, C., Weber, R., Banfield, D., Barrett, E., Bierwirth, M., Calcutt, S., Compaire, N., Johnson, C. L., Mance, D., Euchner, F., Kerjean, L., Mainsant, G., Mocquet, A., Rodriguez Manfredi, J. A., Pont, G., Laudet, P., Nebut, T., De Raucourt, S., Robert, O., Russell, C. T., Sylvestre-Baron, A., Tillier, S., Warren, T., Wieczorek, M., Yana, C., and Zweifel, P.
Abstract: The crust beneath the InSight lander on Mars is altered or fractured to 8-11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight's seismometer. Mars's seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth's microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight's Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8-11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.
Published: 2020

14. The seismicity of Mars

Author: Giardini, D., Lognonne, P., Banerdt, W. B., Pike, W. T., Christensen, U., Ceylan, S., Clinton, J. F., van Driel, M., Staehler, S. C., Boese, M., Garcia, R. F., Khan, A., Panning, M., Perrin, C., Banfield, D., Beucler, E., Charalambous, C., Euchner, F., Horleston, A., Jacob, A., Kawamura, T., Kedar, S., Mainsant, G., Scholz, J. -R., Smrekar, S. E., Spiga, A., Agard, C., Antonangeli, D., Barkaoui, S., Barrett, E., Combes, P., Conejero, V., Daubar, I., Drilleau, M., Ferrier, C., Gabsi, T., Gudkova, T., Hurst, K., Karakostas, F., King, S., Knapmeyer, M., Knapmeyer-Endrun, B., Llorca-Cejudo, R., Lucas, A., Luno, L., Margerin, L., McClean, J. B., Mimoun, D., Murdoch, N., Nimmo, F., Nonon, M., Pardo, C., Rivoldini, A., Manfredi, J. A. Rodriguez, Samuel, H., Schimmel, M., Stott, A. E., Stutzmann, E., Teanby, N., Warren, T., Weber, R. C., Wieczorek, M., Yana, C., Giardini, D., Lognonne, P., Banerdt, W. B., Pike, W. T., Christensen, U., Ceylan, S., Clinton, J. F., van Driel, M., Staehler, S. C., Boese, M., Garcia, R. F., Khan, A., Panning, M., Perrin, C., Banfield, D., Beucler, E., Charalambous, C., Euchner, F., Horleston, A., Jacob, A., Kawamura, T., Kedar, S., Mainsant, G., Scholz, J. -R., Smrekar, S. E., Spiga, A., Agard, C., Antonangeli, D., Barkaoui, S., Barrett, E., Combes, P., Conejero, V., Daubar, I., Drilleau, M., Ferrier, C., Gabsi, T., Gudkova, T., Hurst, K., Karakostas, F., King, S., Knapmeyer, M., Knapmeyer-Endrun, B., Llorca-Cejudo, R., Lucas, A., Luno, L., Margerin, L., McClean, J. B., Mimoun, D., Murdoch, N., Nimmo, F., Nonon, M., Pardo, C., Rivoldini, A., Manfredi, J. A. Rodriguez, Samuel, H., Schimmel, M., Stott, A. E., Stutzmann, E., Teanby, N., Warren, T., Weber, R. C., Wieczorek, M., and Yana, C.
Abstract: The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019. The mission aims to detect, characterize and locate seismic activity on Mars, and to further constrain the internal structure, composition and dynamics of the planet. Here, we present seismometer data recorded until 30 September 2019, which reveal that Mars is seismically active. We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude M-w 3-4 with waves propagating at various depths in the mantle. These marsquakes have spectral characteristics similar to the seismicity observed on the Earth and Moon. We determine that two of the largest detected marsquakes were located near the Cerberus Fossae fracture system. From the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-S-wave-velocity layer in the upper mantle. Mars is seismically active: 24 subcrustal magnitude 3-4 marsquakes and 150 smaller events have been identified up to 30 September 2019, by an analysis of seismometer data from the InSight lander.
Published: 2020

15. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data

Author: Lognonne, P., Banerdt, W. B., Pike, W. T., Giardini, D., Christensen, U., Garcia, R. F., Kawamura, T., Kedar, S., Knapmeyer-Endrun, B., Margerin, L., Nimmo, F., Panning, M., Tauzin, B., Scholz, J. -R., Antonangeli, D., Barkaoui, S., Beucler, E., Bissig, F., Brinkman, N., Calvet, M., Ceylan, S., Charalambous, C., Davis, P., Van Driel, M., Drilleau, M., Fayon, L., Joshi, R., Kenda, B., Khan, A., Knapmeyer, M., Lekic, V., McClean, J., Mimoun, D., Murdoch, N., Pan, L., Perrin, C., Pinot, B., Pou, L., Menina, S., Rodriguez, S., Schmelzbach, C., Schmerr, N., Sollberger, D., Spiga, A., Staehler, S., Stott, A., Stutzmann, E., Tharimena, S., Widmer-Schnidrig, R., Andersson, F., Ansan, V., Beghein, C., Boese, M., Bozdag, E., Clinton, J., Daubar, I., Delage, P., Fuji, N., Golombek, M., Grott, M., Horleston, A., Hurst, K., Irving, J., Jacob, A., Knollenberg, J., Krasner, S., Krause, C., Lorenz, R., Michaut, C., Myhill, R., Nissen-Meyer, T., Ten Pierick, J., Plesa, A. -C., Quantin-Nataf, C., Robertsson, J., Rochas, L., Schimmel, M., Smrekar, S., Spohn, T., Teanby, N., Tromp, J., Vallade, J., Verdier, N., Vrettos, C., Weber, R., Banfield, D., Barrett, E., Bierwirth, M., Calcutt, S., Compaire, N., Johnson, C. L., Mance, D., Euchner, F., Kerjean, L., Mainsant, G., Mocquet, A., Rodriguez Manfredi, J. A., Pont, G., Laudet, P., Nebut, T., De Raucourt, S., Robert, O., Russell, C. T., Sylvestre-Baron, A., Tillier, S., Warren, T., Wieczorek, M., Yana, C., Zweifel, P., Lognonne, P., Banerdt, W. B., Pike, W. T., Giardini, D., Christensen, U., Garcia, R. F., Kawamura, T., Kedar, S., Knapmeyer-Endrun, B., Margerin, L., Nimmo, F., Panning, M., Tauzin, B., Scholz, J. -R., Antonangeli, D., Barkaoui, S., Beucler, E., Bissig, F., Brinkman, N., Calvet, M., Ceylan, S., Charalambous, C., Davis, P., Van Driel, M., Drilleau, M., Fayon, L., Joshi, R., Kenda, B., Khan, A., Knapmeyer, M., Lekic, V., McClean, J., Mimoun, D., Murdoch, N., Pan, L., Perrin, C., Pinot, B., Pou, L., Menina, S., Rodriguez, S., Schmelzbach, C., Schmerr, N., Sollberger, D., Spiga, A., Staehler, S., Stott, A., Stutzmann, E., Tharimena, S., Widmer-Schnidrig, R., Andersson, F., Ansan, V., Beghein, C., Boese, M., Bozdag, E., Clinton, J., Daubar, I., Delage, P., Fuji, N., Golombek, M., Grott, M., Horleston, A., Hurst, K., Irving, J., Jacob, A., Knollenberg, J., Krasner, S., Krause, C., Lorenz, R., Michaut, C., Myhill, R., Nissen-Meyer, T., Ten Pierick, J., Plesa, A. -C., Quantin-Nataf, C., Robertsson, J., Rochas, L., Schimmel, M., Smrekar, S., Spohn, T., Teanby, N., Tromp, J., Vallade, J., Verdier, N., Vrettos, C., Weber, R., Banfield, D., Barrett, E., Bierwirth, M., Calcutt, S., Compaire, N., Johnson, C. L., Mance, D., Euchner, F., Kerjean, L., Mainsant, G., Mocquet, A., Rodriguez Manfredi, J. A., Pont, G., Laudet, P., Nebut, T., De Raucourt, S., Robert, O., Russell, C. T., Sylvestre-Baron, A., Tillier, S., Warren, T., Wieczorek, M., Yana, C., and Zweifel, P.
Abstract: The crust beneath the InSight lander on Mars is altered or fractured to 8-11 km depth and may bear volatiles, according to an analysis of seismic noise and wave scattering recorded by InSight's seismometer. Mars's seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth's microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight's Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8-11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.
Published: 2020

16. The seismicity of Mars

Author: Giardini, D., Lognonne, P., Banerdt, W. B., Pike, W. T., Christensen, U., Ceylan, S., Clinton, J. F., van Driel, M., Staehler, S. C., Boese, M., Garcia, R. F., Khan, A., Panning, M., Perrin, C., Banfield, D., Beucler, E., Charalambous, C., Euchner, F., Horleston, A., Jacob, A., Kawamura, T., Kedar, S., Mainsant, G., Scholz, J. -R., Smrekar, S. E., Spiga, A., Agard, C., Antonangeli, D., Barkaoui, S., Barrett, E., Combes, P., Conejero, V., Daubar, I., Drilleau, M., Ferrier, C., Gabsi, T., Gudkova, T., Hurst, K., Karakostas, F., King, S., Knapmeyer, M., Knapmeyer-Endrun, B., Llorca-Cejudo, R., Lucas, A., Luno, L., Margerin, L., McClean, J. B., Mimoun, D., Murdoch, N., Nimmo, F., Nonon, M., Pardo, C., Rivoldini, A., Manfredi, J. A. Rodriguez, Samuel, H., Schimmel, M., Stott, A. E., Stutzmann, E., Teanby, N., Warren, T., Weber, R. C., Wieczorek, M., Yana, C., Giardini, D., Lognonne, P., Banerdt, W. B., Pike, W. T., Christensen, U., Ceylan, S., Clinton, J. F., van Driel, M., Staehler, S. C., Boese, M., Garcia, R. F., Khan, A., Panning, M., Perrin, C., Banfield, D., Beucler, E., Charalambous, C., Euchner, F., Horleston, A., Jacob, A., Kawamura, T., Kedar, S., Mainsant, G., Scholz, J. -R., Smrekar, S. E., Spiga, A., Agard, C., Antonangeli, D., Barkaoui, S., Barrett, E., Combes, P., Conejero, V., Daubar, I., Drilleau, M., Ferrier, C., Gabsi, T., Gudkova, T., Hurst, K., Karakostas, F., King, S., Knapmeyer, M., Knapmeyer-Endrun, B., Llorca-Cejudo, R., Lucas, A., Luno, L., Margerin, L., McClean, J. B., Mimoun, D., Murdoch, N., Nimmo, F., Nonon, M., Pardo, C., Rivoldini, A., Manfredi, J. A. Rodriguez, Samuel, H., Schimmel, M., Stott, A. E., Stutzmann, E., Teanby, N., Warren, T., Weber, R. C., Wieczorek, M., and Yana, C.
Abstract: The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019. The mission aims to detect, characterize and locate seismic activity on Mars, and to further constrain the internal structure, composition and dynamics of the planet. Here, we present seismometer data recorded until 30 September 2019, which reveal that Mars is seismically active. We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude M-w 3-4 with waves propagating at various depths in the mantle. These marsquakes have spectral characteristics similar to the seismicity observed on the Earth and Moon. We determine that two of the largest detected marsquakes were located near the Cerberus Fossae fracture system. From the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-S-wave-velocity layer in the upper mantle. Mars is seismically active: 24 subcrustal magnitude 3-4 marsquakes and 150 smaller events have been identified up to 30 September 2019, by an analysis of seismometer data from the InSight lander.
Published: 2020

17. InSight seismic data from Mars: Effect and treatment of transient data disturbances.

Author: Widmer-Schnidrig, Rudolf, Scholz, J. R., Davis, Paul, Lognonné, P., Pinot, Baptiste, García, Raphael, Hurst, K., Pou, Laurent, Nimmo, F., Barkaoui, Salma, De Raucourt, Sebastien, Knapmeyer‐Endrun, Brigitte, Knapmeyer, M., Orhand-Mainsant, Guenolé, Compaire, Nicolas, Cuvier, Arthur, Beucler, E., Bonnin, Mickaël J. A., Joshi, Rakshit, Sainton, G., Stutzmann, E., Schimmel, Martin, Horleston, Anna C., Böse, M., Ceylan, S., Clinton, John F., van Driel, M., Kawamura, T., Khan, A., Staehler, Simon C., Giardini, Domenico, Charalambous, C., Stott, Alexander, Pike, William T., Christensen, U., Banerdt, William B., Widmer-Schnidrig, Rudolf, Scholz, J. R., Davis, Paul, Lognonné, P., Pinot, Baptiste, García, Raphael, Hurst, K., Pou, Laurent, Nimmo, F., Barkaoui, Salma, De Raucourt, Sebastien, Knapmeyer‐Endrun, Brigitte, Knapmeyer, M., Orhand-Mainsant, Guenolé, Compaire, Nicolas, Cuvier, Arthur, Beucler, E., Bonnin, Mickaël J. A., Joshi, Rakshit, Sainton, G., Stutzmann, E., Schimmel, Martin, Horleston, Anna C., Böse, M., Ceylan, S., Clinton, John F., van Driel, M., Kawamura, T., Khan, A., Staehler, Simon C., Giardini, Domenico, Charalambous, C., Stott, Alexander, Pike, William T., Christensen, U., and Banerdt, William B.
Abstract: The instrument package SEIS (Seismic Experiment for Internal Structure) with the two co-located seismometers VBB and SP is installed on the surface of Mars as part of NASA's InSight mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. The daily atmospheric temperature variations of approx. 80K are attenuated by different insulation layers to approx. 15K peak-to-peak at the sensor level. Typical wind speeds vary between 0 and 5 m/s leading to a diurnal variation in the broad-band rms noise level by two orders of magnitude. One ubiquitous artifact in the raw broad-band data is an abundance of one-sided, transient pulses often accompanied by high-frequency spikes. We show that these pulses, which we term "glitches", can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to intermittent stress relaxation events internal to SEIS caused by the large diurnal temperature variations to which the instrument is exposed during a Martian sol. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of the instrument. Whilst such kind of data disturbances are typically discarded when occurring in terrestrial data, this is no option for the data returned from the Red Planet. We therefore do not only demonstrate their effects on the seismic data and analyze their origins, but also propose algorithms that are able to detect and remove many of these (mostly) non-seismic signals. We further published our codes (both Python and MATLAB) so that interested researchers can make their own choices on how to treat the data and to which extent.
Published: 2020

18. Detection, Analysis, and Removal of Glitches From InSight's Seismic Data From Mars

Author: Agence Nationale de la Recherche (France), Swiss Space Office, Schimmel, Martin [0000-0003-2601-4462], Scholz, J. R., Widmer‐Schnidrig, Rudolf, Davis, Paul, Lognonné, P., Pinot, Baptiste, Garcia, Raphael F., Hurst, K., Pou, Laurent, Nimmo, F., Barkaoui, Salma, De Raucourt, Sebastien, Knapmeyer‐Endrun, Brigitte, Knapmeyer, M., Orhand-Mainsant, Guenolé, Compaire, Nicolas, Cuvier, Arthur, Beucler, E., Bonnin, Mickaël, Joshi, Rakshit, Sainton, G., Stutzmann, E., Schimmel, Martin, Horleston, Anna, Böse, M., Ceylan, S., Clinton, John F., van Driel, M., Kawamura, T., Khan, A., Stähler, S. C., Giardini, Domenico, Charalambous, C., Stott, A. E., Pike, William T., Christensen, U., Banerdt, William B., Agence Nationale de la Recherche (France), Swiss Space Office, Schimmel, Martin [0000-0003-2601-4462], Scholz, J. R., Widmer‐Schnidrig, Rudolf, Davis, Paul, Lognonné, P., Pinot, Baptiste, Garcia, Raphael F., Hurst, K., Pou, Laurent, Nimmo, F., Barkaoui, Salma, De Raucourt, Sebastien, Knapmeyer‐Endrun, Brigitte, Knapmeyer, M., Orhand-Mainsant, Guenolé, Compaire, Nicolas, Cuvier, Arthur, Beucler, E., Bonnin, Mickaël, Joshi, Rakshit, Sainton, G., Stutzmann, E., Schimmel, Martin, Horleston, Anna, Böse, M., Ceylan, S., Clinton, John F., van Driel, M., Kawamura, T., Khan, A., Stähler, S. C., Giardini, Domenico, Charalambous, C., Stott, A. E., Pike, William T., Christensen, U., and Banerdt, William B.
Abstract: The instrument package SEIS (Seismic Experiment for Internal Structure) with the three very broadband and three short‐period seismic sensors is installed on the surface on Mars as part of NASA's InSight Discovery mission. When compared to terrestrial installations, SEIS is deployed in a very harsh wind and temperature environment that leads to inevitable degradation of the quality of the recorded data. One ubiquitous artifact in the raw data is an abundance of transient one‐sided pulses often accompanied by high‐frequency spikes. These pulses, which we term “glitches”, can be modeled as the response of the instrument to a step in acceleration, while the spikes can be modeled as the response to a simultaneous step in displacement. We attribute the glitches primarily to SEIS‐internal stress relaxations caused by the large temperature variations to which the instrument is exposed during a Martian day. Only a small fraction of glitches correspond to a motion of the SEIS package as a whole caused by minuscule tilts of either the instrument or the ground. In this study, we focus on the analysis of the glitch+spike phenomenon and present how these signals can be automatically detected and removed from SEIS's raw data. As glitches affect many standard seismological analysis methods such as receiver functions, spectral decomposition and source inversions, we anticipate that studies of the Martian seismicity as well as studies of Mars' internal structure should benefit from deglitched seismic data.
Published: 2020

19. Constraints on the shallow elastic and anelastic structure of Mars from InSight seismic data

Author: Centre National D'Etudes Spatiales (France), California Institute of Technology, NASA Astrobiology Institute (US), Swiss National Science Foundation, European Commission, Schimmel, Martin [0000-0003-2601-4462], Lognonné, P., Banerdt, W. B., Pike, William T., Giardini, Domenico, Christensen, U., Garcia, R. F., Kawamura, T., Kedar, S., Knapmeyer‐Endrun, Brigitte, Margerin, L., Nimmo, F., Daubar, I., Delage, P., Fuji, N., Golombek, M., Grott, M., Horleston, A., Hurst, K., Irving, J., Jacob, A., Knollenberg, J., Krasner, S., Krause, C., Lorenz, R., Michaut, C., Myhill, Robert, Nissen-Meyer, T., ten Pierick, J., Plesa, A. C., Quantin-Nataf, C., Robertsson, J., Rochas, L., Schimmel, Martin, Smrekar, S., Spohn, T., Teanby, N., Tromp, J., Vallade, J., Verdier, N., Vrettos, C., Weber, R., Banfield, D., Barrett, E., Bierwirth, M., Calcutt, S., Compaire, N., Johnson, C. L., Mance, D., Euchner, F., Kerjean, L., Mainsant, G., Mocquet, A., Rodriguez Manfredi, J. A., Pont, G., Laudet, P., Nebut, T., de Raucourt, S., Robert, O., Russell, C. T., Sylvestre-Baron, A., Tillier, S., Warren, T., Wieczorek, M., Yana, C., Zweifel, P., Panning, M., Tauzin, B., Scholz, J. R., Antonangeli, D., Barkaoui, S., Beucler, E., Bissig, F., Brinkman, N., Calvet, M., Ceylan, S., Charalambous, C., Davis, P., van Driel, M., Drilleau, M., Fayon, L., Joshi, R., Kenda, B., Khan, A., Knapmeyer, M., Lekic, Vedran, McClean, J., Mimoun, D., Murdoch, N., Pan, L., Perrin , C., Pinot, B, Pou, L., Menina, S., Rodríguez, S., Schmelzbach, C., Schmerr, N., Sollberger, D., Spiga, A., Stähler, S., Stott, A., Stutzmann, E., Tharimena, S., Widmer-Schnidrig, R., Andersson, F., Ansan, V., Beghein, C., Böse, M., Bozdag, E., Clinton, John F., Centre National D'Etudes Spatiales (France), California Institute of Technology, NASA Astrobiology Institute (US), Swiss National Science Foundation, European Commission, Schimmel, Martin [0000-0003-2601-4462], Lognonné, P., Banerdt, W. B., Pike, William T., Giardini, Domenico, Christensen, U., Garcia, R. F., Kawamura, T., Kedar, S., Knapmeyer‐Endrun, Brigitte, Margerin, L., Nimmo, F., Daubar, I., Delage, P., Fuji, N., Golombek, M., Grott, M., Horleston, A., Hurst, K., Irving, J., Jacob, A., Knollenberg, J., Krasner, S., Krause, C., Lorenz, R., Michaut, C., Myhill, Robert, Nissen-Meyer, T., ten Pierick, J., Plesa, A. C., Quantin-Nataf, C., Robertsson, J., Rochas, L., Schimmel, Martin, Smrekar, S., Spohn, T., Teanby, N., Tromp, J., Vallade, J., Verdier, N., Vrettos, C., Weber, R., Banfield, D., Barrett, E., Bierwirth, M., Calcutt, S., Compaire, N., Johnson, C. L., Mance, D., Euchner, F., Kerjean, L., Mainsant, G., Mocquet, A., Rodriguez Manfredi, J. A., Pont, G., Laudet, P., Nebut, T., de Raucourt, S., Robert, O., Russell, C. T., Sylvestre-Baron, A., Tillier, S., Warren, T., Wieczorek, M., Yana, C., Zweifel, P., Panning, M., Tauzin, B., Scholz, J. R., Antonangeli, D., Barkaoui, S., Beucler, E., Bissig, F., Brinkman, N., Calvet, M., Ceylan, S., Charalambous, C., Davis, P., van Driel, M., Drilleau, M., Fayon, L., Joshi, R., Kenda, B., Khan, A., Knapmeyer, M., Lekic, Vedran, McClean, J., Mimoun, D., Murdoch, N., Pan, L., Perrin , C., Pinot, B, Pou, L., Menina, S., Rodríguez, S., Schmelzbach, C., Schmerr, N., Sollberger, D., Spiga, A., Stähler, S., Stott, A., Stutzmann, E., Tharimena, S., Widmer-Schnidrig, R., Andersson, F., Ansan, V., Beghein, C., Böse, M., Bozdag, E., and Clinton, John F.
Abstract: Mars’s seismic activity and noise have been monitored since January 2019 by the seismometer of the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. At night, Mars is extremely quiet; seismic noise is about 500 times lower than Earth’s microseismic noise at periods between 4 s and 30 s. The recorded seismic noise increases during the day due to ground deformations induced by convective atmospheric vortices and ground-transferred wind-generated lander noise. Here we constrain properties of the crust beneath InSight, using signals from atmospheric vortices and from the hammering of InSight’s Heat Flow and Physical Properties (HP3) instrument, as well as the three largest Marsquakes detected as of September 2019. From receiver function analysis, we infer that the uppermost 8–11 km of the crust is highly altered and/or fractured. We measure the crustal diffusivity and intrinsic attenuation using multiscattering analysis and find that seismic attenuation is about three times larger than on the Moon, which suggests that the crust contains small amounts of volatiles.
Published: 2020

20. The seismicity of Mars

Author: Swiss National Supercomputing Centre, Swiss National Science Foundation, Agence Nationale de la Recherche (France), State Secretariat for Education, Research and Innovation (Switzerland), UK Space Agency, California Institute of Technology, German Centre for Air and Space Travel, Schimmel, Martin [0000-0003-2601-4462], Giardini, Domenico, Lognonné, P., Banerdt, W. B., Pike, William T., Christensen, U., Ceylan, S., Clinton, John F., van Driel, M., Stähler, S. C., Böse, M., Garcia, R. F., Khan, A., Panning, M., Perrin, C., Banfield, D., Beucler, E., Charalambous, C., Euchner, F., Horleston, A., Jacob, A., Kawamura, T., Kedar, S., Mainsant, G., Scholz, J. R., Smrekar, S. E., Spiga, A., Agard, C., Antonangeli, D., Barkaoui, S., Barrett, E., Combes, P., Conejero, Vicente, Daubar, I., Drilleau, M., Ferrier, C., Gabsi, T., Gudkova, T., Hurst, K., Karakostas, F., King, S., Knapmeyer, M., Knapmeyer‐Endrun, Brigitte, Llorca-Cejudo, R., Lucas, A., Luno, L., Margerin, L., McClean, J. B., Mimoun, D., Murdoch, N., Nimmo, F., Nonon, M., Pardo, C., Rivoldini, A., Manfredi, J. A. R., Samuel, H., Schimmel, Martin, Stott, A. E., Stutzmann, E., Teanby, N., Warren, T., Weber, R. C., Wieczorek, M., Yana, C., Swiss National Supercomputing Centre, Swiss National Science Foundation, Agence Nationale de la Recherche (France), State Secretariat for Education, Research and Innovation (Switzerland), UK Space Agency, California Institute of Technology, German Centre for Air and Space Travel, Schimmel, Martin [0000-0003-2601-4462], Giardini, Domenico, Lognonné, P., Banerdt, W. B., Pike, William T., Christensen, U., Ceylan, S., Clinton, John F., van Driel, M., Stähler, S. C., Böse, M., Garcia, R. F., Khan, A., Panning, M., Perrin, C., Banfield, D., Beucler, E., Charalambous, C., Euchner, F., Horleston, A., Jacob, A., Kawamura, T., Kedar, S., Mainsant, G., Scholz, J. R., Smrekar, S. E., Spiga, A., Agard, C., Antonangeli, D., Barkaoui, S., Barrett, E., Combes, P., Conejero, Vicente, Daubar, I., Drilleau, M., Ferrier, C., Gabsi, T., Gudkova, T., Hurst, K., Karakostas, F., King, S., Knapmeyer, M., Knapmeyer‐Endrun, Brigitte, Llorca-Cejudo, R., Lucas, A., Luno, L., Margerin, L., McClean, J. B., Mimoun, D., Murdoch, N., Nimmo, F., Nonon, M., Pardo, C., Rivoldini, A., Manfredi, J. A. R., Samuel, H., Schimmel, Martin, Stott, A. E., Stutzmann, E., Teanby, N., Warren, T., Weber, R. C., Wieczorek, M., and Yana, C.
Abstract: The InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018 and fully deployed its seismometer by the end of February 2019. The mission aims to detect, characterize and locate seismic activity on Mars, and to further constrain the internal structure, composition and dynamics of the planet. Here, we present seismometer data recorded until 30 September 2019, which reveal that Mars is seismically active. We identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude Mw 3–4 with waves propagating at various depths in the mantle. These marsquakes have spectral characteristics similar to the seismicity observed on the Earth and Moon. We determine that two of the largest detected marsquakes were located near the Cerberus Fossae fracture system. From the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-S-wave-velocity layer in the upper mantle. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
Published: 2020

21. Modeling glacial flow on and onto Pluto’s Sputnik Planitia

Author: Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology. Department of Aeronautics and Astronautics, Umurhan, O.M., Howard, A.D., Moore, J.M., Earle, Alissa Michelle, White, O.L., Schenk, P.M., Binzel, Richard P, Stern, S.A., Beyer, R.A., Nimmo, F., McKinnon, W.B., Ennico, K., Olkin, C.B., Weaver, H.A., Young, L.A., Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology. Department of Aeronautics and Astronautics, Umurhan, O.M., Howard, A.D., Moore, J.M., Earle, Alissa Michelle, White, O.L., Schenk, P.M., Binzel, Richard P, Stern, S.A., Beyer, R.A., Nimmo, F., McKinnon, W.B., Ennico, K., Olkin, C.B., Weaver, H.A., and Young, L.A.
Abstract: Observations of Pluto's surface made by the New Horizons spacecraft indicate present-day N2 ice glaciation in and around the basin informally known as Sputnik Planitia. Motivated by these observations, we have developed an evolutionary glacial flow model of solid N2 ice that takes into account its published thermophysical and rheological properties. This model assumes that glacial ice flows laminarly and has a low aspect ratio which permits a vertically integrated mathematical formulation. We assess the conditions for the validity of laminar N2 ice motion by revisiting the problem of the onset of solid-state buoyant convection of N2 ice for a variety of bottom thermal boundary conditions. Subject to uncertainties in N2 ice rheology, N2 ice layers are estimated to flow laminarly for thicknesses less than 400–1000 m. The resulting mass-flux formulation for when the N2 ice flows as a laminar dry glacier is characterized by an Arrhenius–Glen functional form. The flow model developed is used here to qualitatively answer some questions motivated by features we interpret to be a result of glacial flow found on Sputnik Planitia. We find that the wavy transverse dark features found along the northern shoreline of Sputnik Planitia may be a transitory imprint of shallow topography just beneath the ice surface suggesting the possibility that a major shoreward flow event happened relatively recently, within the last few hundred years. Model results also support the interpretation that the prominent darkened features resembling flow lobes observed along the eastern shoreline of the Sputnik Planitia basin may be the result of a basally wet N2 glacier flowing into the basin from the pitted highlands of eastern Tombaugh Regio.
Published: 2020

22. Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto

Author: Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Nimmo, F., Hamilton, D. P., McKinnon, W. B., Schenk, P. M., Bierson, C. J., Beyer, R. A., Moore, J. M., Stern, S. A., Weaver, H. A., Olkin, C. B., Young, L. A., Smith, K. E., New Horizons Geology, Geophysics and Imaging Theme Team, Binzel, Richard P, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Nimmo, F., Hamilton, D. P., McKinnon, W. B., Schenk, P. M., Bierson, C. J., Beyer, R. A., Moore, J. M., Stern, S. A., Weaver, H. A., Olkin, C. B., Young, L. A., Smith, K. E., New Horizons Geology, Geophysics and Imaging Theme Team, and Binzel, Richard P
Abstract: The deep nitrogen-covered basin on Pluto, informally named Sputnik Planitia, is located very close to the longitude of Pluto's tidal axis and may be an impact feature, by analogy with other large basins in the Solar System. Reorientation of Sputnik Planitia arising from tidal and rotational torques can explain the basin's present-day location, but requires the feature to be a positive gravity anomaly, despite its negative topography. Here we argue that if Sputnik Planitia did indeed form as a result of an impact and if Pluto possesses a subsurface ocean, the required positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by later modest nitrogen deposition. Without a subsurface ocean, a positive gravity anomaly requires an implausibly thick nitrogen layer (exceeding 40 kilometres). To prolong the lifetime of such a subsurface ocean to the present day and to maintain ocean uplift, a rigid, conductive water-ice shell is required. Because nitrogen deposition is latitude-dependent, nitrogen loading and reorientation may have exhibited complex feedbacks.
Published: 2020

23. Near-equilibrium isotope fractionation during planetesimal evaporation

Author: Young, E. D., Shahar, A., Nimmo, F., Schlichting, H. E., Schauble, E. A., Tang, H., Labidi, J., Young, E. D., Shahar, A., Nimmo, F., Schlichting, H. E., Schauble, E. A., Tang, H., and Labidi, J.
Abstract: Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. We evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controlled attendant isotope fractionations. Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order < 1 meter that would be subject to foundering. Bodies that are massive enough to form magma oceans by radioisotope decay (ge 0.1%) can retain hot rock vapor even in the absence of ambient nebular gas. We find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. Numerical simulations of this near-equilibrium evaporation process for a body with a radius of ~ 700 km yield a steady-state far-field vapor pressure corresponding to 95% saturation. Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas. We model the Si and Mg isotopic composition of bulk Earth and show that the best fit is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium evaporation into the solar protostellar disk of hydrogen gas on timescales of 10,000 to 100,000 years., Comment: 35 pages, 15 figures
Published: 2019
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24. Formation of Charon's Red Poles From Seasonally Cold-Trapped Volatiles

Author: Grundy, W. M., Cruikshank, D. P., Gladstone, G. R., Howett, C. J. A., Lauer, T. R., Spencer, J. R., Summers, M. E., Buie, M. W., Earle, A. M., Ennico, K., Parker, J. Wm., Porter, S. B., Singer, K. N., Stern, S. A., Verbiscer, A. J., Beyer, R. A., Binzel, R. P., Buratti, B. J., Cook, J. C., Ore, C. M. Dalle, Olkin, C. B., Parker, A. H., Protopapa, S., Quirico, E., Retherford, K. D., Robbins, S. J., Schmitt, B., Stansberry, J. A., Umurhan, O. M., Weaver, H. A., Young, L. A., Zangari, A. M., Bray, V. J., Cheng, A. F., McKinnon, W. B., McNutt Jr., R. L., Moore, J. M., Nimmo, F., Reuter, D. C., Schenk, P. M., Team, the New Horizons Science, Grundy, W. M., Cruikshank, D. P., Gladstone, G. R., Howett, C. J. A., Lauer, T. R., Spencer, J. R., Summers, M. E., Buie, M. W., Earle, A. M., Ennico, K., Parker, J. Wm., Porter, S. B., Singer, K. N., Stern, S. A., Verbiscer, A. J., Beyer, R. A., Binzel, R. P., Buratti, B. J., Cook, J. C., Ore, C. M. Dalle, Olkin, C. B., Parker, A. H., Protopapa, S., Quirico, E., Retherford, K. D., Robbins, S. J., Schmitt, B., Stansberry, J. A., Umurhan, O. M., Weaver, H. A., Young, L. A., Zangari, A. M., Bray, V. J., Cheng, A. F., McKinnon, W. B., McNutt Jr., R. L., Moore, J. M., Nimmo, F., Reuter, D. C., Schenk, P. M., and Team, the New Horizons Science
Abstract: A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location of this material on Charon implicates the temperature extremes that result from Charon's high obliquity and long seasons. The escape of Pluto's atmosphere provides a potential feed stock for production of complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase showing the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon, the supply and temporary cold-trapping of material escaping from Pluto, and, while cold-trapped, its photolytic processing into more complex and less volatile molecules. The model results are consistent with the proposed mechanism producing the observed colour pattern on Charon.
Published: 2019
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25. Reorientation of Sputnik Planitia implies a Subsurface Ocean on Pluto

Author: Nimmo, F., Hamilton, D. P., Schenk, W. B. McKinnon P. M., Binzel, R. P., Bierson, C. J., Beyer, R. A., Moore, J. M., Stern, S. A., Weaver, H. A., Olkin, C., Young, L. A., Smith, K. E., Spencer, J. R., Buie, M., Buratti, B., Cheng, A., Cruikshank, D., Ore, C. Dalle, Earle, A., Gladstone, R., Grundy, W., Howard, A. D., Lauer, T., Linscott, I., Parker, J., Porter, S., Reitsema, H., Reuter, D., Roberts, J. H., Robbins, S., Showalter, M., Singer, K., Strobel, D., Summers, M., Tyler, L., Weaver, H., White, O. L., Umurhan, O. M., Banks, M., Barnouin, O., Bray, V., Carcich, B., Chaikin, A., Chavez, C., Conrad, C., Howett, C., Hofgartner, J., Kammer, J., Lisse, C., Marcotte, A., Parker, A., Retherford, K., Saina, M., Runyon, K., Schindhelm, R., Stansberry, J., Steffl, A., Stryk, T., Throop, . H., Tsang, C., Verbiscer, A., Winters, H., Zangari, A., Nimmo, F., Hamilton, D. P., Schenk, W. B. McKinnon P. M., Binzel, R. P., Bierson, C. J., Beyer, R. A., Moore, J. M., Stern, S. A., Weaver, H. A., Olkin, C., Young, L. A., Smith, K. E., Spencer, J. R., Buie, M., Buratti, B., Cheng, A., Cruikshank, D., Ore, C. Dalle, Earle, A., Gladstone, R., Grundy, W., Howard, A. D., Lauer, T., Linscott, I., Parker, J., Porter, S., Reitsema, H., Reuter, D., Roberts, J. H., Robbins, S., Showalter, M., Singer, K., Strobel, D., Summers, M., Tyler, L., Weaver, H., White, O. L., Umurhan, O. M., Banks, M., Barnouin, O., Bray, V., Carcich, B., Chaikin, A., Chavez, C., Conrad, C., Howett, C., Hofgartner, J., Kammer, J., Lisse, C., Marcotte, A., Parker, A., Retherford, K., Saina, M., Runyon, K., Schindhelm, R., Stansberry, J., Steffl, A., Stryk, T., Throop, . H., Tsang, C., Verbiscer, A., Winters, H., and Zangari, A.
Abstract: The deep nitrogen-covered Sputnik Planitia (SP; informal name) basin on Pluto is located very close to the longitude of Pluto's tidal axis[1] and may be an impact feature [2], by analogy with other large basins in the solar system[3,4]. Reorientation[5-7] due to tidal and rotational torques can explain SP's location, but requires it to be a positive gravity anomaly[7], despite its negative topography. Here we argue that if SP formed via impact and if Pluto possesses a subsurface ocean, a positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by later modest N2 deposition. Without a subsurface ocean a positive gravity anomaly requires an implausibly thick N2 layer (greater than 40 km). A rigid, conductive ice shell is required to prolong such an ocean's lifetime to the present day[8] and maintain ocean uplift. Because N2 deposition is latitude-dependent[9], nitrogen loading and reorientation may have exhibited complex feedbacks[7].
Published: 2019
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26. Near-equilibrium isotope fractionation during planetesimal evaporation.

Author: Young, ED, Young, ED, Shahar, A, Nimmo, F, Schlichting, HE, Schauble, EA, Tang, H, Labidi, J, Young, ED, Young, ED, Shahar, A, Nimmo, F, Schlichting, HE, Schauble, EA, Tang, H, and Labidi, J
Abstract: Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. We evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controled attendant isotope fractionations. Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order < 1 meter that would be subject to foundering. Bodies that are massive enough to form magma oceans by radioisotope decay (≥ 0.1% M ⊕) can retain hot rock vapor even in the absence of ambient nebular gas. We find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. Numerical simulations of this near-equilibrium evaporation process for a body with a radius of ~ 700 km yield a steady-state far-field vapor pressure of 10-8 bar and a vapor pressure at the surface of 10-4 bar, corresponding to 95% saturation. Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas. We model the Si and Mg isotopic composition of bulk Earth as a consequence of accretion of planetesimals that evaporated subject to the conditions described above. The results show that the best fit to bulk Earth is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium evaporation into the solar protostellar disk of H2 on
Published: 2019

27. Reorientation of Sputnik Planitia implies a Subsurface Ocean on Pluto

Author: Nimmo, F., Hamilton, D. P., Schenk, W. B. McKinnon P. M., Binzel, R. P., Bierson, C. J., Beyer, R. A., Moore, J. M., Stern, S. A., Weaver, H. A., Olkin, C., Young, L. A., Smith, K. E., Spencer, J. R., Buie, M., Buratti, B., Cheng, A., Cruikshank, D., Ore, C. Dalle, Earle, A., Gladstone, R., Grundy, W., Howard, A. D., Lauer, T., Linscott, I., Parker, J., Porter, S., Reitsema, H., Reuter, D., Roberts, J. H., Robbins, S., Showalter, M., Singer, K., Strobel, D., Summers, M., Tyler, L., Weaver, H., White, O. L., Umurhan, O. M., Banks, M., Barnouin, O., Bray, V., Carcich, B., Chaikin, A., Chavez, C., Conrad, C., Howett, C., Hofgartner, J., Kammer, J., Lisse, C., Marcotte, A., Parker, A., Retherford, K., Saina, M., Runyon, K., Schindhelm, R., Stansberry, J., Steffl, A., Stryk, T., Throop, . H., Tsang, C., Verbiscer, A., Winters, H., Zangari, A., Nimmo, F., Hamilton, D. P., Schenk, W. B. McKinnon P. M., Binzel, R. P., Bierson, C. J., Beyer, R. A., Moore, J. M., Stern, S. A., Weaver, H. A., Olkin, C., Young, L. A., Smith, K. E., Spencer, J. R., Buie, M., Buratti, B., Cheng, A., Cruikshank, D., Ore, C. Dalle, Earle, A., Gladstone, R., Grundy, W., Howard, A. D., Lauer, T., Linscott, I., Parker, J., Porter, S., Reitsema, H., Reuter, D., Roberts, J. H., Robbins, S., Showalter, M., Singer, K., Strobel, D., Summers, M., Tyler, L., Weaver, H., White, O. L., Umurhan, O. M., Banks, M., Barnouin, O., Bray, V., Carcich, B., Chaikin, A., Chavez, C., Conrad, C., Howett, C., Hofgartner, J., Kammer, J., Lisse, C., Marcotte, A., Parker, A., Retherford, K., Saina, M., Runyon, K., Schindhelm, R., Stansberry, J., Steffl, A., Stryk, T., Throop, . H., Tsang, C., Verbiscer, A., Winters, H., and Zangari, A.
Abstract: The deep nitrogen-covered Sputnik Planitia (SP; informal name) basin on Pluto is located very close to the longitude of Pluto's tidal axis[1] and may be an impact feature [2], by analogy with other large basins in the solar system[3,4]. Reorientation[5-7] due to tidal and rotational torques can explain SP's location, but requires it to be a positive gravity anomaly[7], despite its negative topography. Here we argue that if SP formed via impact and if Pluto possesses a subsurface ocean, a positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by later modest N2 deposition. Without a subsurface ocean a positive gravity anomaly requires an implausibly thick N2 layer (greater than 40 km). A rigid, conductive ice shell is required to prolong such an ocean's lifetime to the present day[8] and maintain ocean uplift. Because N2 deposition is latitude-dependent[9], nitrogen loading and reorientation may have exhibited complex feedbacks[7].
Published: 2019
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28. Formation of Charon's Red Poles From Seasonally Cold-Trapped Volatiles

Author: Grundy, W. M., Cruikshank, D. P., Gladstone, G. R., Howett, C. J. A., Lauer, T. R., Spencer, J. R., Summers, M. E., Buie, M. W., Earle, A. M., Ennico, K., Parker, J. Wm., Porter, S. B., Singer, K. N., Stern, S. A., Verbiscer, A. J., Beyer, R. A., Binzel, R. P., Buratti, B. J., Cook, J. C., Ore, C. M. Dalle, Olkin, C. B., Parker, A. H., Protopapa, S., Quirico, E., Retherford, K. D., Robbins, S. J., Schmitt, B., Stansberry, J. A., Umurhan, O. M., Weaver, H. A., Young, L. A., Zangari, A. M., Bray, V. J., Cheng, A. F., McKinnon, W. B., McNutt Jr., R. L., Moore, J. M., Nimmo, F., Reuter, D. C., Schenk, P. M., Team, the New Horizons Science, Grundy, W. M., Cruikshank, D. P., Gladstone, G. R., Howett, C. J. A., Lauer, T. R., Spencer, J. R., Summers, M. E., Buie, M. W., Earle, A. M., Ennico, K., Parker, J. Wm., Porter, S. B., Singer, K. N., Stern, S. A., Verbiscer, A. J., Beyer, R. A., Binzel, R. P., Buratti, B. J., Cook, J. C., Ore, C. M. Dalle, Olkin, C. B., Parker, A. H., Protopapa, S., Quirico, E., Retherford, K. D., Robbins, S. J., Schmitt, B., Stansberry, J. A., Umurhan, O. M., Weaver, H. A., Young, L. A., Zangari, A. M., Bray, V. J., Cheng, A. F., McKinnon, W. B., McNutt Jr., R. L., Moore, J. M., Nimmo, F., Reuter, D. C., Schenk, P. M., and Team, the New Horizons Science
Abstract: A unique feature of Pluto's large satellite Charon is its dark red northern polar cap. Similar colours on Pluto's surface have been attributed to organic macromolecules produced by energetic radiation processing of hydrocarbons. The polar location of this material on Charon implicates the temperature extremes that result from Charon's high obliquity and long seasons. The escape of Pluto's atmosphere provides a potential feed stock for production of complex chemistry. Gas from Pluto that is transiently cold-trapped and processed at Charon's winter pole was proposed as an explanation on the basis of an image of Charon's northern hemisphere, but not modelled quantitatively. Here we report images of the southern hemisphere illuminated by Pluto-shine and also images taken during the approach phase showing the northern polar cap over a range of longitudes. We model the surface thermal environment on Charon, the supply and temporary cold-trapping of material escaping from Pluto, and, while cold-trapped, its photolytic processing into more complex and less volatile molecules. The model results are consistent with the proposed mechanism producing the observed colour pattern on Charon.
Published: 2019
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29. Near-equilibrium isotope fractionation during planetesimal evaporation

Author: Young, E. D., Shahar, A., Nimmo, F., Schlichting, H. E., Schauble, E. A., Tang, H., Labidi, J., Young, E. D., Shahar, A., Nimmo, F., Schlichting, H. E., Schauble, E. A., Tang, H., and Labidi, J.
Abstract: Silicon and Mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. We evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controlled attendant isotope fractionations. Energy balance at the surface of a body accreted within ~1 Myr of CAI formation and heated from within by 26Al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order < 1 meter that would be subject to foundering. Bodies that are massive enough to form magma oceans by radioisotope decay (ge 0.1%) can retain hot rock vapor even in the absence of ambient nebular gas. We find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. Vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. Numerical simulations of this near-equilibrium evaporation process for a body with a radius of ~ 700 km yield a steady-state far-field vapor pressure corresponding to 95% saturation. Approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas. We model the Si and Mg isotopic composition of bulk Earth and show that the best fit is for a carbonaceous chondrite-like source material with about 12% loss of Mg and 15% loss of Si resulting from near-equilibrium evaporation into the solar protostellar disk of hydrogen gas on timescales of 10,000 to 100,000 years., Comment: 35 pages, 15 figures
Published: 2019
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30. SEIS first year: nm/s^2 (and less) broadband seismology on Mars and first steps in Mars-Earth-Moon comparative seismology. (Invited)

Author: Lognonné, P., Banerdt, William B., Pike, William T., Giardini, Domenico, Banfield, D., Christensen, U., Beucler, E., Bierwirth, Marco, Calcutt, Simon B., Daubar, I., Clinton, John F., Kedar, S., Gabsi, T., Garcia, Raphael G., Hurst, K., Kawamura, T., Knapmeyer‐Endrun, Brigitte, Margerin, Ludovic, Mimoun, D., Nimmo, F., Panning, Mark P., De Raucourt, Sebastien, Schmerr, Nicholas C., Smrekar, Suzanne, Spiga, A., Teanby, Nicholas A., Weber, R. C., Wieczorek, M., Zweifel, Peter, Yana, C., Barkaoui, Salma, Brinkman, N., Ceylan, S., Conejero, Vicente, Compaire, Nicolas, Charalambous, C., Davis, Paul, van Driel, M., Drilleau, M., Fayon, Lucile, Kenda, B., Mance, Davor, McClean, John, Murdoch, N., Nebut, Tanguy, Pardo, Constanza, Pinot, Baptiste, Pou, Laurent, Perrin, C., Sainton, G., Sollberger, David, Scholz, J. R., Staehler, Simon C., Roberts, Oliver, Schmelzbach, C., Stott, A., Schimmel, Martin, Stutzmann, E., Tillier, Sylvain, Verdier, Nicolas, Warren, T., Widmer-Schnidrig, Rudolf, Böse, M., Euchner, F., Horleston, Anna C., Khan, A., Orhand-Mainsant, Guenolé, Barrett, E., Gaudin, E., Kerjean, Laurent, Julien, Agnès, Nonon, M., Llorca-Cejudo, R., Laudet, Philippe, Maki, Justin, Mouret, Jean-Marie, Pont, Gabriel, Meunier, Frederic A., Rochas, Ludovic, de Larclause, Isabel Savin, Sylvestre-Baron, Annick, Trebi-Ollenu, Ashitey, Valladeau, J., Delage, P., Jacob, A., Calvet, Marie, Grotte, M., Rodríguez-Manfredi, José Antonio, Lekic, Vedran, Menina, Sabrina, Robertsson, John O.A., Spohn, Tilman, Tauzin, Benoit, Tharimena, S., Pierick, Jen Ten, Lognonné, P., Banerdt, William B., Pike, William T., Giardini, Domenico, Banfield, D., Christensen, U., Beucler, E., Bierwirth, Marco, Calcutt, Simon B., Daubar, I., Clinton, John F., Kedar, S., Gabsi, T., Garcia, Raphael G., Hurst, K., Kawamura, T., Knapmeyer‐Endrun, Brigitte, Margerin, Ludovic, Mimoun, D., Nimmo, F., Panning, Mark P., De Raucourt, Sebastien, Schmerr, Nicholas C., Smrekar, Suzanne, Spiga, A., Teanby, Nicholas A., Weber, R. C., Wieczorek, M., Zweifel, Peter, Yana, C., Barkaoui, Salma, Brinkman, N., Ceylan, S., Conejero, Vicente, Compaire, Nicolas, Charalambous, C., Davis, Paul, van Driel, M., Drilleau, M., Fayon, Lucile, Kenda, B., Mance, Davor, McClean, John, Murdoch, N., Nebut, Tanguy, Pardo, Constanza, Pinot, Baptiste, Pou, Laurent, Perrin, C., Sainton, G., Sollberger, David, Scholz, J. R., Staehler, Simon C., Roberts, Oliver, Schmelzbach, C., Stott, A., Schimmel, Martin, Stutzmann, E., Tillier, Sylvain, Verdier, Nicolas, Warren, T., Widmer-Schnidrig, Rudolf, Böse, M., Euchner, F., Horleston, Anna C., Khan, A., Orhand-Mainsant, Guenolé, Barrett, E., Gaudin, E., Kerjean, Laurent, Julien, Agnès, Nonon, M., Llorca-Cejudo, R., Laudet, Philippe, Maki, Justin, Mouret, Jean-Marie, Pont, Gabriel, Meunier, Frederic A., Rochas, Ludovic, de Larclause, Isabel Savin, Sylvestre-Baron, Annick, Trebi-Ollenu, Ashitey, Valladeau, J., Delage, P., Jacob, A., Calvet, Marie, Grotte, M., Rodríguez-Manfredi, José Antonio, Lekic, Vedran, Menina, Sabrina, Robertsson, John O.A., Spohn, Tilman, Tauzin, Benoit, Tharimena, S., and Pierick, Jen Ten
Abstract: InSight is the first planetary mission with a seismometer package, SEIS, since the Apollo Lunar Surface Experiments Package. SEIS is complimented by APSS, which has as a goal to document the atmospheric source of seismic noise and signals. Since June 2019, SEIS has been delivering 6 axis 20 sps continuous seismic data, a rate one order of magnitude larger originally planned. More than 50 events have been detected by the end of July 2019 but only three have amplitudes significantly above the SEIS instrument requirement. Two have clear and coherent arrivals of P and S waves, enabling location, diffusion/attenuation characterization and receiver function analysis. The event¿s magnitudes are likely ¿ 3 and no clear surface waves nor deep interior phases have been identified. This suggests deep events with scattering along their final propagation paths and with large propagation differences as compared to Earth and Moon quakes. Most of the event¿s detections are made possible due to the very low noise achieved by the instrument installation strategy and the very low VBB self-noise. Most of the SEIS signals have amplitudes of spectral densities in the 0.03-5Hz frequency bandwidth ranging from 10-10 m/s2/Hz1/2 to 5 10-9 m/s2/Hz1/2. The smallest noise levels occurs during the early night, with angstrom displacements or nano-radian tilts. This monitors the elastic and seismic interaction of a planetary surface with its atmosphere, illustrated not only by a wide range of SEIS signals correlated with pressure vortexes, dust devils or wind activity but also by modulation of resonances above 1 Hz, amplified by ultra-low velocity surface layers. After about one half of a Martian year, clear seasonal changes appear also in the noise, which will be discussed. One year after landing, the seismic noise is therefore better and better understood, and noise correction techniques begun to be implemented, either thanks to the APSS wind and pressure sensors, or by SEIS only data processing
Published: 2019

31. Plume Origins and Plumbing: From Ocean to Surface

Author: Schenk, Paul M., Clark, Roger N., Howett, Carly J. A., Verbiscer, Anne J., Waite, J. Hunter, Spencer, J. R., Nimmo, F., Ingersoll, Andrew P., Hurford, T. A., Kite, E. S., Rhoden, A. R., Schmidt, J., Howett, C. J. A., Schenk, Paul M., Clark, Roger N., Howett, Carly J. A., Verbiscer, Anne J., Waite, J. Hunter, Spencer, J. R., Nimmo, F., Ingersoll, Andrew P., Hurford, T. A., Kite, E. S., Rhoden, A. R., Schmidt, J., and Howett, C. J. A.
Abstract: The plume of Enceladus provides a unique window into subsurface processes in the ice shell and ocean of an icy world. Thanks to a decade of observations and modeling, a coherent picture is emerging of a thin ice shell extending across the south polar region, cut through by fractures directly connected to the underlying ocean, and at least partially filled with water. The plume jets emerging from the fractures directly sample this water reservoir. The shell undergoes daily tidal flexing, which modulates plume activity by opening and closing the fractures. Dissipation in the ice and conduit water components due to this flexing is likely to generate the several gigawatts of observed power that are lost from the south pole as infrared radiation and plume latent heat.
Published: 2018

32. Modeling glacial flow on and onto Pluto's Sputnik Planitia

Author: Umurhan, O. M., Howard, A. D., Moore, J. M., Earle, A. M., Binzel, R. P., Stern, S. A., Schenk, P. M., Beyer, R. A., White, O. L., NImmo, F., McKinnon, W. B., Ennico, K., Olkin, C. B., Weaver, H. A., Young, L. A., Umurhan, O. M., Howard, A. D., Moore, J. M., Earle, A. M., Binzel, R. P., Stern, S. A., Schenk, P. M., Beyer, R. A., White, O. L., NImmo, F., McKinnon, W. B., Ennico, K., Olkin, C. B., Weaver, H. A., and Young, L. A.
Abstract: Observations of Pluto's surface made by the New Horizons spacecraft indicates present-day nitrogen ice glaciation in and around the basin known as Sputnik Planum. Motivated by these observations, we have developed an evolutionary glacial flow model of solid nitrogen ice taking into account its published thermophysical and rheologies properties. This model assumes that glacial ice layers flow laminarly and have low aspect ratios which permits a vertically integrated mathematical formulation. We assess the conditions for the validity of laminar nitrogen ice motion by revisiting the problem of the onset of solid-state buoyant convection of nitrogen ice for a variety of bottom thermal boundary conditions. Subject to uncertainties in nitrogen ice rheology, nitrogen ice layers are estimated to flow laminarly for thicknesses less than 400-1000 meters. The resulting mass-flux formulation for when the nitrogen ice flows as a laminar dry glacier is characterized by an Arrhenius-Glen functional form. The flow model developed is used here to qualitatively answer some questions motivated by observed glacial flow features found on Sputnik Planum. We find that the wavy transverse dark features found along the northern shoreline of Sputnik Planum may be a transitory imprint of shallow topography just beneath the ice surface suggesting the possibility that a major shoreward flow event happened relatively recently within the last few hundred years. Model results also support the interpretation that the prominent darkened features resembling flow lobes observed along the eastern shoreline of the Sputnik Planum basin may be a result of wet nitrogen glacial ice flowing into the basin from the pitted highlands of eastern Tombaugh Regio., Comment: This definitive version has several typos corrected including equation expressions in Appendix C.2 and C.3. Updated version with associated errata in process at Icarus (July 26, 2018). All previous results appearing in journal version --especially those pertaining to glacial flow and their related timescales (Sections 4 & 5) -- are unchanged
Published: 2016
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33. The Small Satellites of Pluto as Observed by New Horizons

Author: Weaver, H. A., Buie, M. W., Buratti, B. J., Grundy, W. M., Lauer, T. R., Olkin, C. B., Parker, A. H., Porter, S. B., Showalter, M. R., Spencer, J. R., Stern, S. A., Verbiscer, A. J., McKinnon, W. B., Moore, J. M., Robbins, S. J., Schenk, P., Singer, K. N., Barnouin, O. S., Cheng, A. F., Ernst, C. M., Lisse, C. M., Jennings, D. E., Lunsford, A. W., Reuter, D. C., Hamilton, D. P., Kaufmann, D. E., Ennico, K., Young, L. A., Beyer, R. A., Binzel, R. P., Bray, V. J., Chaikin, A. L., Cook, J. C., Cruikshank, D. P., Ore, C. M. Dalle, Earle, A. M., Gladstone, G. R., Howett, C. J. A., Linscott, I. R., Nimmo, F., Parker, J. Wm., Philippe, S., Protopapa, S., Reitsema, H. J., Schmitt, B., Stryk, T., Summers, M. E., Tsang, C. C. C., Throop, H. H. B., White, O. L., Zangari, A. M., Weaver, H. A., Buie, M. W., Buratti, B. J., Grundy, W. M., Lauer, T. R., Olkin, C. B., Parker, A. H., Porter, S. B., Showalter, M. R., Spencer, J. R., Stern, S. A., Verbiscer, A. J., McKinnon, W. B., Moore, J. M., Robbins, S. J., Schenk, P., Singer, K. N., Barnouin, O. S., Cheng, A. F., Ernst, C. M., Lisse, C. M., Jennings, D. E., Lunsford, A. W., Reuter, D. C., Hamilton, D. P., Kaufmann, D. E., Ennico, K., Young, L. A., Beyer, R. A., Binzel, R. P., Bray, V. J., Chaikin, A. L., Cook, J. C., Cruikshank, D. P., Ore, C. M. Dalle, Earle, A. M., Gladstone, G. R., Howett, C. J. A., Linscott, I. R., Nimmo, F., Parker, J. Wm., Philippe, S., Protopapa, S., Reitsema, H. J., Schmitt, B., Stryk, T., Summers, M. E., Tsang, C. C. C., Throop, H. H. B., White, O. L., and Zangari, A. M.
Abstract: The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of $\approx$40 km for Nix and Hydra and ~10 km for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of $\approx$2. All four moons have high albedos ( $\approx$50-90 %) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages $\gtrsim$ 4 Ga. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary., Comment: in Science 351, aae0030 (2016)
Published: 2016
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34. Modeling glacial flow on and onto Pluto's Sputnik Planitia

Author: Umurhan, O. M., Howard, A. D., Moore, J. M., Earle, A. M., Binzel, R. P., Stern, S. A., Schenk, P. M., Beyer, R. A., White, O. L., NImmo, F., McKinnon, W. B., Ennico, K., Olkin, C. B., Weaver, H. A., Young, L. A., Umurhan, O. M., Howard, A. D., Moore, J. M., Earle, A. M., Binzel, R. P., Stern, S. A., Schenk, P. M., Beyer, R. A., White, O. L., NImmo, F., McKinnon, W. B., Ennico, K., Olkin, C. B., Weaver, H. A., and Young, L. A.
Abstract: Observations of Pluto's surface made by the New Horizons spacecraft indicates present-day nitrogen ice glaciation in and around the basin known as Sputnik Planum. Motivated by these observations, we have developed an evolutionary glacial flow model of solid nitrogen ice taking into account its published thermophysical and rheologies properties. This model assumes that glacial ice layers flow laminarly and have low aspect ratios which permits a vertically integrated mathematical formulation. We assess the conditions for the validity of laminar nitrogen ice motion by revisiting the problem of the onset of solid-state buoyant convection of nitrogen ice for a variety of bottom thermal boundary conditions. Subject to uncertainties in nitrogen ice rheology, nitrogen ice layers are estimated to flow laminarly for thicknesses less than 400-1000 meters. The resulting mass-flux formulation for when the nitrogen ice flows as a laminar dry glacier is characterized by an Arrhenius-Glen functional form. The flow model developed is used here to qualitatively answer some questions motivated by observed glacial flow features found on Sputnik Planum. We find that the wavy transverse dark features found along the northern shoreline of Sputnik Planum may be a transitory imprint of shallow topography just beneath the ice surface suggesting the possibility that a major shoreward flow event happened relatively recently within the last few hundred years. Model results also support the interpretation that the prominent darkened features resembling flow lobes observed along the eastern shoreline of the Sputnik Planum basin may be a result of wet nitrogen glacial ice flowing into the basin from the pitted highlands of eastern Tombaugh Regio., Comment: This definitive version has several typos corrected including equation expressions in Appendix C.2 and C.3. Updated version with associated errata in process at Icarus (July 26, 2018). All previous results appearing in journal version --especially those pertaining to glacial flow and their related timescales (Sections 4 & 5) -- are unchanged
Published: 2016
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35. The Small Satellites of Pluto as Observed by New Horizons

Author: Weaver, H. A., Buie, M. W., Buratti, B. J., Grundy, W. M., Lauer, T. R., Olkin, C. B., Parker, A. H., Porter, S. B., Showalter, M. R., Spencer, J. R., Stern, S. A., Verbiscer, A. J., McKinnon, W. B., Moore, J. M., Robbins, S. J., Schenk, P., Singer, K. N., Barnouin, O. S., Cheng, A. F., Ernst, C. M., Lisse, C. M., Jennings, D. E., Lunsford, A. W., Reuter, D. C., Hamilton, D. P., Kaufmann, D. E., Ennico, K., Young, L. A., Beyer, R. A., Binzel, R. P., Bray, V. J., Chaikin, A. L., Cook, J. C., Cruikshank, D. P., Ore, C. M. Dalle, Earle, A. M., Gladstone, G. R., Howett, C. J. A., Linscott, I. R., Nimmo, F., Parker, J. Wm., Philippe, S., Protopapa, S., Reitsema, H. J., Schmitt, B., Stryk, T., Summers, M. E., Tsang, C. C. C., Throop, H. H. B., White, O. L., Zangari, A. M., Weaver, H. A., Buie, M. W., Buratti, B. J., Grundy, W. M., Lauer, T. R., Olkin, C. B., Parker, A. H., Porter, S. B., Showalter, M. R., Spencer, J. R., Stern, S. A., Verbiscer, A. J., McKinnon, W. B., Moore, J. M., Robbins, S. J., Schenk, P., Singer, K. N., Barnouin, O. S., Cheng, A. F., Ernst, C. M., Lisse, C. M., Jennings, D. E., Lunsford, A. W., Reuter, D. C., Hamilton, D. P., Kaufmann, D. E., Ennico, K., Young, L. A., Beyer, R. A., Binzel, R. P., Bray, V. J., Chaikin, A. L., Cook, J. C., Cruikshank, D. P., Ore, C. M. Dalle, Earle, A. M., Gladstone, G. R., Howett, C. J. A., Linscott, I. R., Nimmo, F., Parker, J. Wm., Philippe, S., Protopapa, S., Reitsema, H. J., Schmitt, B., Stryk, T., Summers, M. E., Tsang, C. C. C., Throop, H. H. B., White, O. L., and Zangari, A. M.
Abstract: The New Horizons mission has provided resolved measurements of Pluto's moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of $\approx$40 km for Nix and Hydra and ~10 km for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of $\approx$2. All four moons have high albedos ( $\approx$50-90 %) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages $\gtrsim$ 4 Ga. The small moons rotate much faster than synchronous, with rotational poles clustered nearly orthogonal to the common pole directions of Pluto and Charon. These results reinforce the hypothesis that the small moons formed in the aftermath of a collision that produced the Pluto-Charon binary., Comment: in Science 351, aae0030 (2016)
Published: 2016
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36. Formation of the Orientale lunar multiring basin

Author: Johnson, B., Blair, D., Collins, G., Melosh, H., Freed, A., Taylor, G., Head, J., Wieczorek, M., Andrews-Hanna, J., Nimmo, F., Keane, J., Miljkovic, Katarina, Soderblom, J., Zuber, M., Johnson, B., Blair, D., Collins, G., Melosh, H., Freed, A., Taylor, G., Head, J., Wieczorek, M., Andrews-Hanna, J., Nimmo, F., Keane, J., Miljkovic, Katarina, Soderblom, J., and Zuber, M.
Abstract: Multiring basins, large impact craters characterized by multiple concentric topographic rings, dominate the stratigraphy, tectonics, and crustal structure of the Moon. Using a hydrocode, we simulated the formation of the Orientale multiring basin, producing a subsurface structure consistent with high-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft. The simulated impact produced a transient crater, ~390 kilometers in diameter, that was not maintained because of subsequent gravitational collapse. Our simulations indicate that the flow of warm weak material at depth was crucial to the formation of the basin's outer rings, which are large normal faults that formed at different times during the collapse stage. The key parameters controlling ring location and spacing are impactor diameter and lunar thermal gradients.
Published: 2016

37. Gravity field of the orientale basin from the gravity recovery and interior laboratory mission

Author: Zuber, M., Smith, D., Neumann, G., Goossens, S., Andrews-Hanna, J., Head, J., Kiefer, W., Asmar, S., Konopliv, A., Lemoine, F., Matsuyama, I., Melosh, H., McGovern, P., Nimmo, F., Phillips, R., Solomon, S., Taylor, G., Watkins, M., Wieczorek, M., Williams, J., Jansen, J., Johnson, B., Keane, J., Mazarico, E., Miljkovic, Katarina, Park, R., Soderblom, J., Yuan, D., Zuber, M., Smith, D., Neumann, G., Goossens, S., Andrews-Hanna, J., Head, J., Kiefer, W., Asmar, S., Konopliv, A., Lemoine, F., Matsuyama, I., Melosh, H., McGovern, P., Nimmo, F., Phillips, R., Solomon, S., Taylor, G., Watkins, M., Wieczorek, M., Williams, J., Jansen, J., Johnson, B., Keane, J., Mazarico, E., Miljkovic, Katarina, Park, R., Soderblom, J., and Yuan, D.
Abstract: The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 ± 0.2) × 106 km3 of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.
Published: 2016

38. The Pluto system: Initial results from its exploration by New Horizons

Author: Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt Jr., R. L., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, R., Sepan, B., Showalter, M. R., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webbert, R., Weidner, S., Weigle II, G. E., White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., Zirnstein, E., Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt Jr., R. L., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, R., Sepan, B., Showalter, M. R., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webbert, R., Weidner, S., Weigle II, G. E., White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., and Zirnstein, E.
Abstract: The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition, its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected., Comment: 8 pages - Initial Science paper from NASA's New Horizons Pluto Encounter
Published: 2015
Full Text: View/download PDF

39. The Pluto system: Initial results from its exploration by New Horizons

Author: Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt, R. L., Jr., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, E., Sepan, B., Showalter, M. K., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webber, R., Weidner, S., Weigle, G. E., II, White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., Zirnstein, E., Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt, R. L., Jr., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, E., Sepan, B., Showalter, M. K., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webber, R., Weidner, S., Weigle, G. E., II, White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., and Zirnstein, E.
Abstract: The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.
Published: 2015

40. The Pluto system: Initial results from its exploration by New Horizons

Author: Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt, R. L., Jr., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, E., Sepan, B., Showalter, M. K., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webber, R., Weidner, S., Weigle, G. E., II, White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., Zirnstein, E., Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt, R. L., Jr., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, E., Sepan, B., Showalter, M. K., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webber, R., Weidner, S., Weigle, G. E., II, White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., and Zirnstein, E.
Abstract: The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected.
Published: 2015

41. The Pluto system: Initial results from its exploration by New Horizons

Author: Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt Jr., R. L., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, R., Sepan, B., Showalter, M. R., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webbert, R., Weidner, S., Weigle II, G. E., White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., Zirnstein, E., Stern, S. A., Bagenal, F., Ennico, K., Gladstone, G. R., Grundy, W. M., McKinnon, W. B., Moore, J. M., Olkin, C. B., Spencer, J. R., Weaver, H. A., Young, L. A., Andert, T., Andrews, J., Banks, M., Bauer, B., Bauman, J., Barnouin, O. S., Bedini, P., Beisser, K., Beyer, R. A., Bhaskaran, S., Binzel, R. P., Birath, E., Bird, M., Bogan, D. J., Bowman, A., Bray, V. J., Brozovic, M., Bryan, C., Buckley, M. R., Buie, M. W., Buratti, B. J., Bushman, S. S., Calloway, A., Carcich, B., Cheng, A. F., Conard, S., Conrad, C. A., Cook, J. C., Cruikshank, D. P., Custodio, O. S., Ore, C. M. Dalle, Deboy, C., Dischner, Z. J. B., Dumont, P., Earle, A. M., Elliott, H. A., Ercol, J., Ernst, C. M., Finley, T., Flanigan, S. H., Fountain, G., Freeze, M. J., Greathouse, T., Green, J. L., Guo, Y., Hahn, M., Hamilton, D. P., Hamilton, S. A., Hanley, J., Harch, A., Hart, H. M., Hersman, C. B., Hill, A., Hill, M. E., Hinson, D. P., Holdridge, M. E., Horanyi, M., Howard, A. D., Howett, C. J. A., Jackman, C., Jacobson, R. A., Jennings, D. E., Kammer, J. A., Kang, H. K., Kaufmann, D. E., Kollmann, P., Krimigis, S. M., Kusnierkiewicz, D., Lauer, T. R., Lee, J. E., Lindstrom, K. L., Linscott, I. R., Lisse, C. M., Lunsford, A. W., Mallder, V. A., Martin, N., McComas, D. J., McNutt Jr., R. L., Mehoke, D., Mehoke, T., Melin, E. D., Mutchler, M., Nelson, D., Nimmo, F., Nunez, J. I., Ocampo, A., Owen, W. M., Paetzold, M., Page, B., Parker, A. H., Parker, J. W., Pelletier, F., Peterson, J., Pinkine, N., Piquette, M., Porter, S. B., Protopapa, S., Redfern, J., Reitsema, H. J., Reuter, D. C., Roberts, J. H., Robbins, S. J., Rogers, G., Rose, D., Runyon, K., Retherford, K. D., Ryschkewitsch, M. G., Schenk, P., Schindhelm, R., Sepan, B., Showalter, M. R., Singer, K. N., Soluri, M., Stanbridge, D., Steffl, A. J., Strobel, D. F., Stryk, T., Summers, M. E., Szalay, J. R., Tapley, M., Taylor, A., Taylor, H., Throop, H. B., Tsang, C. C. C., Tyler, G. L., Umurhan, O. M., Verbiscer, A. J., Versteeg, M. H., Vincent, M., Webbert, R., Weidner, S., Weigle II, G. E., White, O. L., Whittenburg, K., Williams, B. G., Williams, K., Williams, S., Woods, W. W., Zangari, A. M., and Zirnstein, E.
Abstract: The Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. Pluto's large moon Charon displays tectonics and evidence for a heterogeneous crustal composition, its north pole displays puzzling dark terrain. Small satellites Hydra and Nix have higher albedos than expected., Comment: 8 pages - Initial Science paper from NASA's New Horizons Pluto Encounter
Published: 2015
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42. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements

Author: Neumann, G., Zuber, M., Wieczorek, M., Head, J., Baker, D., Solomon, S., Smith, D., Lemoine, F., Mazarico, E., Sabaka, T., Goossens, S., Melosh, H., Phillips, R., Asmar, S., Konopliv, A., Williams, J., Sori, M., Soderblom, J., Miljkovic, Katarina, Andrews-Hanna, J., Nimmo, F., Kiefer, W., Neumann, G., Zuber, M., Wieczorek, M., Head, J., Baker, D., Solomon, S., Smith, D., Lemoine, F., Mazarico, E., Sabaka, T., Goossens, S., Melosh, H., Phillips, R., Asmar, S., Konopliv, A., Williams, J., Sori, M., Soderblom, J., Miljkovic, Katarina, Andrews-Hanna, J., Nimmo, F., and Kiefer, W.
Abstract: Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population.
Published: 2015

43. The fractured Moon: Production and saturation of porosity in the lunar highlands from impact cratering

Author: Soderblom, J., Evans, A., Johnson, B., Melosh, H., Miljkovic, Katarina, Phillips, R., Andrews-Hanna, J., Bierson, C., Head, J., Milbury, C., Neumann, G., Nimmo, F., Smith, D., Solomon, S., Sori, M., Wieczorek, M., Zuber, M., Soderblom, J., Evans, A., Johnson, B., Melosh, H., Miljkovic, Katarina, Phillips, R., Andrews-Hanna, J., Bierson, C., Head, J., Milbury, C., Neumann, G., Nimmo, F., Smith, D., Solomon, S., Sori, M., Wieczorek, M., and Zuber, M.
Abstract: ©2015. American Geophysical Union. All Rights Reserved. We have analyzed the Bouguer anomaly (BA) of ~1200 complex craters in the lunar highlands from Gravity Recovery and Interior Laboratory observations. The BA of these craters is generally negative, though positive BA values are observed, particularly for smaller craters. Crater BA values scale inversely with crater diameter, quantifying how larger impacts produce more extensive fracturing and dilatant bulking. The Bouguer anomaly of craters larger than 93-19+47 km in diameter is independent of crater size, indicating that there is a limiting depth to impact-generated porosity, presumably from pore collapse associated with either overburden pressure or viscous flow. Impact-generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than ~30 km in diameter, consistent with an ~8 km thick lunar megaregolith, whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces.
Published: 2015

44. Tidal heating in icy satellite oceans

Author: Chen, EMA, Chen, EMA, Nimmo, F, Glatzmaier, GA, Chen, EMA, Chen, EMA, Nimmo, F, and Glatzmaier, GA
Abstract: Tidal heating plays a significant role in the evolution of many satellites in the outer Solar System; however, it is unclear whether tidal dissipation in a global liquid ocean can represent a significant additional heat source. Tyler (Tyler, R.H. [2008]. Nature 456, 770-772; Tyler, R.H. [2009]. Geophys. Res. Lett. 36, doi:10.1029/2009GL038300) suggested that obliquity tides could drive large-scale flow in the oceans of Europa and Enceladus, leading to significant heating. A critical unknown in this previous work is what the tidal quality factor, Q, of such an ocean should be. The corresponding tidal dissipation spans orders of magnitude depending on the value of Q assumed. To address this issue we adopt an approach employed in terrestrial ocean modeling, where a significant portion of tidal dissipation arises due to bottom drag, with the drag coefficient O (0.001) being relatively well-established. From numerical solutions to the shallow-water equations including nonlinear bottom drag, we obtain scalings for the equivalent value of Q as a function of this drag coefficient. In addition, we provide new scaling relations appropriate for the inclusion of ocean tidal heating in thermal-orbital evolution models. Our approach is appropriate for situations in which the ocean bottom topography is much smaller than the ocean thickness. Using these novel scalings, we calculate the ocean contribution to the overall thermal energy budgets for many of the outer Solar System satellites. Although uncertainties such as ocean thickness and satellite obliquity remain, we find that for most satellites it is unlikely that ocean tidal dissipation is important when compared to either radiogenic or solid-body tidal heating. Of known satellites, Triton is the most likely icy satellite to have ocean tidal heating play a role in its present day thermal budget and long-term thermal evolution. © 2013 Elsevier Inc.
Published: 2014

45. Science goals and mission concept for the future exploration of Titan and Enceladus

Author: Tobie, G., Teanby, N. A., Coustenis, A., Jaumann, R., Raulin, E., Schmidt, J., Carrasco, N., Coates, Aj., Cordier, D., De Kok, R., Geppert, Wolf D., Lebreton, J. -P, Lefevre, A., Livengood, T. A., Mandt, K. E., Mitri, G., Nimmo, F., Nixon, C. A., Norman, L., Pappalardo, R. T., Postberg, F., Rodriguez, S., SchuizeMakuch, D., Soderblom, J. M., Solomonidou, A., Stephan, K., Stofan, E. R., Turtle, E. P., Wagner, R. J., West, R. A., Westlake, J. H., Tobie, G., Teanby, N. A., Coustenis, A., Jaumann, R., Raulin, E., Schmidt, J., Carrasco, N., Coates, Aj., Cordier, D., De Kok, R., Geppert, Wolf D., Lebreton, J. -P, Lefevre, A., Livengood, T. A., Mandt, K. E., Mitri, G., Nimmo, F., Nixon, C. A., Norman, L., Pappalardo, R. T., Postberg, F., Rodriguez, S., SchuizeMakuch, D., Soderblom, J. M., Solomonidou, A., Stephan, K., Stofan, E. R., Turtle, E. P., Wagner, R. J., West, R. A., and Westlake, J. H.
Abstract: Saturn's moons, Titan and Enceladus, are two of the Solar System's most enigmatic bodies and are prime targets for future space exploration. Titan provides an analogue for many processes relevant to the Earth, more generally to outer Solar System bodies, and a growing host of newly discovered icy exoplanets. Processes represented include atmospheric dynamics, complex organic chemistry, meteorological cycles (with methane as a working fluid), astrobiology, surface liquids and lakes, geology, fluvial and aeolian erosion, and interactions with an external plasma environment. In addition, exploring Enceladus over multiple targeted flybys will give us a unique opportunity to further study the most active icy moon in our Solar System as revealed by Cassini and to analyse in situ its active plume with highly capable instrumentation addressing its complex chemistry and dynamics. Enceladus' plume likely represents the most accessible samples from an extra-terrestrial liquid water environment in the Solar system, which has far reaching implications for many areas of planetary and biological science. Titan with its massive atmosphere and Enceladus with its active plume are prime planetary objects in the Outer Solar System to perform in situ investigations. In the present paper, we describe the science goals and key measurements to be performed by a future exploration mission involving a Saturn-Titan orbiter and a Titan balloon, which was proposed to ESA in response to the call for definition of the science themes of the next Large-class mission in 2013. The mission scenario is built around three complementary science goals: (A) Titan as an Earth-like system; (B) Enceladus as an active cryovolcanic moon; and (C) Chemistry of Titan and Enceladus - clues for the origin of life. The proposed measurements would provide a step change in our understanding of planetary processes and evolution, with many orders of magnitude improvement in temporal, spatial, and chemical resolution over, AuthorCount:31
Published: 2014
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46. Tidal heating in icy satellite oceans

Author: Chen, EMA, Chen, EMA, Nimmo, F, Glatzmaier, GA, Chen, EMA, Chen, EMA, Nimmo, F, and Glatzmaier, GA
Abstract: Tidal heating plays a significant role in the evolution of many satellites in the outer Solar System; however, it is unclear whether tidal dissipation in a global liquid ocean can represent a significant additional heat source. Tyler (Tyler, R.H. [2008]. Nature 456, 770-772; Tyler, R.H. [2009]. Geophys. Res. Lett. 36, doi:10.1029/2009GL038300) suggested that obliquity tides could drive large-scale flow in the oceans of Europa and Enceladus, leading to significant heating. A critical unknown in this previous work is what the tidal quality factor, Q, of such an ocean should be. The corresponding tidal dissipation spans orders of magnitude depending on the value of Q assumed. To address this issue we adopt an approach employed in terrestrial ocean modeling, where a significant portion of tidal dissipation arises due to bottom drag, with the drag coefficient O (0.001) being relatively well-established. From numerical solutions to the shallow-water equations including nonlinear bottom drag, we obtain scalings for the equivalent value of Q as a function of this drag coefficient. In addition, we provide new scaling relations appropriate for the inclusion of ocean tidal heating in thermal-orbital evolution models. Our approach is appropriate for situations in which the ocean bottom topography is much smaller than the ocean thickness. Using these novel scalings, we calculate the ocean contribution to the overall thermal energy budgets for many of the outer Solar System satellites. Although uncertainties such as ocean thickness and satellite obliquity remain, we find that for most satellites it is unlikely that ocean tidal dissipation is important when compared to either radiogenic or solid-body tidal heating. Of known satellites, Triton is the most likely icy satellite to have ocean tidal heating play a role in its present day thermal budget and long-term thermal evolution. © 2013 Elsevier Inc.
Published: 2014

47. Five New and Three Improved Mutual Orbits of Transneptunian Binaries

Author: Grundy, W. M., Noll, K. S., Nimmo, F., Roe, H. G., Buie, M. W., Porter, S. B., Benecchi, S. D., Stephens, D. C., Levison, H. F., Stansberry, J. A., Grundy, W. M., Noll, K. S., Nimmo, F., Roe, H. G., Buie, M. W., Porter, S. B., Benecchi, S. D., Stephens, D. C., Levison, H. F., and Stansberry, J. A.
Abstract: We present three improved and five new mutual orbits of transneptunian binary systems (58534) Logos-Zoe, (66652) Borasisi-Pabu, (88611) Teharonhiawako-Sawiskera, (123509) 2000 WK183, (149780) Altjira, 2001 QY297, 2003 QW111, and 2003 QY90 based on Hubble Space Telescope and Keck 2 laser guide star adaptive optics observations. Combining the five new orbit solutions with 17 previously known orbits yields a sample of 22 mutual orbits for which the period P, semimajor axis a, and eccentricity e have been determined. These orbits have mutual periods ranging from 5 to over 800 days, semimajor axes ranging from 1,600 to 37,000 km, eccentricities ranging from 0 to 0.8, and system masses ranging from 2 x 10^17 to 2 x 10^22 kg. Based on the relative brightnesses of primaries and secondaries, most of these systems consist of near equal-sized pairs, although a few of the most massive systems are more lopsided. The observed distribution of orbital properties suggests that the most loosely-bound transneptunian binary systems are only found on dynamically cold heliocentric orbits. Of the 22 known binary mutual or-bits, orientation ambiguities are now resolved for 9, of which 7 are prograde and 2 are retro-grade, consistent with a random distribution of orbital orientations, but not with models predicting a strong preference for retrograde orbits. To the extent that other perturbations are not dominant, the binary systems undergo Kozai oscillations of their eccentricities and inclinations with periods of the order of tens of thousands to millions of years, some with strikingly high amplitudes., Comment: In press in Icarus, 29 pages, 5 figures, 13 tables
Published: 2011
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48. Five New and Three Improved Mutual Orbits of Transneptunian Binaries

Author: Grundy, W. M., Noll, K. S., Nimmo, F., Roe, H. G., Buie, M. W., Porter, S. B., Benecchi, S. D., Stephens, D. C., Levison, H. F., Stansberry, J. A., Grundy, W. M., Noll, K. S., Nimmo, F., Roe, H. G., Buie, M. W., Porter, S. B., Benecchi, S. D., Stephens, D. C., Levison, H. F., and Stansberry, J. A.
Abstract: We present three improved and five new mutual orbits of transneptunian binary systems (58534) Logos-Zoe, (66652) Borasisi-Pabu, (88611) Teharonhiawako-Sawiskera, (123509) 2000 WK183, (149780) Altjira, 2001 QY297, 2003 QW111, and 2003 QY90 based on Hubble Space Telescope and Keck 2 laser guide star adaptive optics observations. Combining the five new orbit solutions with 17 previously known orbits yields a sample of 22 mutual orbits for which the period P, semimajor axis a, and eccentricity e have been determined. These orbits have mutual periods ranging from 5 to over 800 days, semimajor axes ranging from 1,600 to 37,000 km, eccentricities ranging from 0 to 0.8, and system masses ranging from 2 x 10^17 to 2 x 10^22 kg. Based on the relative brightnesses of primaries and secondaries, most of these systems consist of near equal-sized pairs, although a few of the most massive systems are more lopsided. The observed distribution of orbital properties suggests that the most loosely-bound transneptunian binary systems are only found on dynamically cold heliocentric orbits. Of the 22 known binary mutual or-bits, orientation ambiguities are now resolved for 9, of which 7 are prograde and 2 are retro-grade, consistent with a random distribution of orbital orientations, but not with models predicting a strong preference for retrograde orbits. To the extent that other perturbations are not dominant, the binary systems undergo Kozai oscillations of their eccentricities and inclinations with periods of the order of tens of thousands to millions of years, some with strikingly high amplitudes., Comment: In press in Icarus, 29 pages, 5 figures, 13 tables
Published: 2011
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