MODELING SURFACE PROCESSES OCCURRING ON MOONS OF THE OUTER SOLAR SYSTEM

A variety of processes, some with familiar terrestrial analogs, are known to take place on moon surfaces in the outer solar system. In this talk, we discuss the observed features of mass wasting and surface transport seen on both Jupiter’s moon Calisto and one of Saturn’s Trojan moons Helene. We provide a number of numerical models using upgraded version of MARSSIM in support of several hypotheses suggested on behalf of the observations made regarding these objects. Calisto exhibits rolling plains of low albedo materials surrounding relatively high jutting peaks harboring high albedo deposits. Our modeling supports the interpretation that Calisto’s surface is a record of erosion driven by the sublimation of CO₂ and H₂O contained in the bedrock. Both solar insolation and surface re-radiation drives the sublimation leaving behind debris which we interpret to be the observed darkened regolith and, further, the high albedo peaks are water ice deposits on surface cold traps. On the other hand, the 45 km scale Helene, being a milligravity environment, exhibits mysterious looking streaks and grooves of very high albedo materials extending for several kilometers with a down-sloping grade of 7^o-9^o. Helene’s cratered terrain also shows evidence of narrowed septa. The observed surface features suggest some type of advective processes are at play in this system. Our modeling lends support to the suggestion that Helene’s surface materials behave as a Bingham plastic material – our flow modeling with such rheologies can reproduce the observed pattern of streakiness; the overall gradients observed; and the narrowed septa of inter-crater regions.