Microwaving Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus and Phoebe: Insights into the regolith properties and geological history of Saturn's icy satellites

• Published in: Icarus
• Main Authors: Le Gall, Alice, Bonnefoy, Léa, Sultana, Robin, Leyrat, Cedric, Janssen, Michael, Wall, Stephen, Lellouch, Emmanuel
• Other Authors: PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut Universitaire de France (IUF), Ministère de l'Education nationale, de l’Enseignement supérieur et de la Recherche (M.E.N.E.S.R.), Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Cornell Center for Astrophysics and Planetary Science (CCAPS), Cornell University New York, Pôle Planétologie du LESIA, Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDU]Sciences of the Universe [physics]; South pole
• Online Access: https://insu.hal.science/insu-03959108; https://insu.hal.science/insu-03959108/document; https://insu.hal.science/insu-03959108/file/1-s2.0-S0019103523000234-main.pdf; https://doi.org/10.1016/j.icarus.2023.115446

International audience While Saturn's main airless moons are all composed largely of water ice, their respective thermal histories and near environments have led to different regolith compositions and structures. Part of this history is recorded in their subsurface which can be probed by microwaves. Using a combined thermal and radiative transfer model, we here investigate all distant observations acquired in the passive mode of the RADAR on board the Cassini spacecraft (2004–2017) at 2.2-cm wavelength. The joint analysis of the derived disk-integrated emissivities and published radar albedos provides new insights into the purity and maturity of the regolith of Saturn's icy moons. We find that satellite-to-satellite variations and large-scale regional anomalies in microwave signatures primarily reflect different degrees of contamination of the regolith by non-ice compounds. To a lesser extent, they may also point to different concentrations of scatterers in the subsurface; these scatterers must be made of ice and/or void rather than of non-ice contaminants. Enceladus appears to have the cleanest regolith likely due to the geological youth of its surface. Observations also suggest that the current heat flux emanating from this moon is not confined to the South Pole Terrain. In the inner system, the degree of purity of the satellites' regoliths decreases from Enceladus outward likely due to the decrease of the E-ring influx. In the outer system, Phoebe's ring mantles Iapetus' leading hemisphere with a decimetric layer of optically-dark and microwave-absorbent dust. Dione is surprisingly less radar-bright and more emissive than expected from both the observed general trend and the current understanding of its geological history. Another question remains outstanding: why are Saturnian moons, and to a lesser extent Jovian moons, so radar-bright at centimetric wavelengths? Current models assuming purely-random scattering in their subsurface fail to simultaneously reproduce active and passive microwave observations, ...