SM049-05
Weathering of ice on the Jovian and Saturnian satellites

Tuesday, 15 December 2020: 17:46
Virtual
Chris Paranicas1, Nicolas Ligier2, Leonardo Regoli1, Charles Hibbitts1, Tom Nordheim3, Matthew M Hedman4, Peter Kollmann5, Elias Roussos6 and Norbert Krupp6, (1)Johns Hopkins University Applied Physics Laboratory, Laurel, MD, United States, (2)Open University, Milton Keynes, United Kingdom, (3)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (4)University of Idaho, Physics, Moscow, ID, United States, (5)The Applied Physics Laboratory, John Hopkins University, Laurel, MD, United States, (6)Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany
Recorded Presentation
Abstract:
It has long been the view that energetic charged particle radiation can darken ice. Recent work on the inner Saturnian satellites links levels of MeV electron and proton bombardment with global brightness (Hedman et al. 2020). At Saturn, the subject lends itself to careful analysis as inner satellites like Janus and Mimas form macrosignatures while smaller moons like Aegaeon and Methone do not. A macrosignature is a circumplanetary decrease in the flux level along a moon's orbit and it suggests much lower weathering on the body by that particle species in the corresponding energy range. Energetic proton precipitation rates onto Jovian and Saturnian moons might also be connected with ice state. Laboratory results suggest that energetic proton bombardment can lead to a transition from crystalline to amorphous ice at temperatures typical of satellite surfaces in the outer solar system. Research with infrared data on Galileo found Europa and Ganymede to have amorphous ice in the top layer, possibly due to their location within the Jovian radiation belts, while Callisto does not (Hansen and McCord 2004). Ground-based work confirmed these ice distributions (Ligier et al. 2016; 2019). In this talk, we will review some of the recent in situ and remote observations of ice on the inner satellites of Jupiter and Saturn, describe how the ice might be processed by different types of particles, and discuss current controversies.

Hedman, M. M. et al. (2020), Photometric analyses of Saturn's small moons: Aegaeon, Methone, and Pallene are dark; Helene and Calypso are bright, Astron. J., 159.

Hansen, G. B., and T. McCord (2004), Amorphous and crystalline ice on the Galilean satellites: A balance between thermal and radiologic processes, J. Geophys. Res., 109.

Ligier, N., et al. (2016), VLT/SINFONI observations of Europa: New insights into the surface composition, Astron. J., 151.

Ligier, N., et al. (2019), Surface composition and properties of Ganymede: Update from ground-based observations with the near-infrared imaging spectrometer SINFONI/VLT/ESO, Icarus, 333.

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