Abstract
AbstractThe final analysis of the Cassini radar observations of Saturn's icy moons presented here shows that the exchange of material between the planet's dust rings and moons, which is specific to the Saturnian system, plays a key role in the current state of the airless satellite regolith. Far from Saturn, the vast debris ring from Phoebe progressively coats the leading side of Iapetus with optically dark material reducing its radar brightness. On the contrary, close to the planet, the extreme radar brightness of the innermost moons Mimas, Enceladus, and Tethys (that exceeds that of the Galilean satellites) is most likely related to Enceladus's geysers and the E‐ring which brings ultraclean water ice to their surfaces. The measured radar albedos and observed hemispheric dichotomies require at least a few decimeters thick “snow” cover and that the near surfaces of Saturn's innermost moons contain especially efficient backscattering structures whose nature remains an outstanding problem.
Highlights
On 15 September 2017, the Cassini spacecraft plunged into Saturn and burned up in its atmosphere
The final analysis of the Cassini radar observations of Saturn's icy moons presented here shows that the exchange of material between the planet's dust rings and moons, which is specific to the Saturnian system, plays a key role in the current state of the airless satellite regolith
Whether it is due to random scattering or refraction on organized structures, the extremely high radar albedos measured by the Cassini RADAR point to the high degree of purity of the water ice regoliths in Saturn's inner system
Summary
On 15 September 2017, the Cassini spacecraft plunged into Saturn and burned up in its atmosphere. In addition to distant measurements, active spatially resolved data were acquired during one close flyby of Iapetus (Le Gall et al, 2014; Wye, 2011), two close flybys of Enceladus (one partially remaining to be analyzed; Wye, 2011; Le Gall et al, 2017), one close flyby of Rhea (Wye, 2011, reanalyzed for this work, SI) and one close flyby of Dione (this work, SI) These observations provide estimates of regional 2.2‐cm radar albedos that can be added to the analysis.
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