HELENE, CALYPSO, AND TELESTO: SHRINKING SATELLITES WITH DEEP-SEATED MASS WASTING

These small, Lagrangian co-orbital satellites of Dione and Tethys feature generally smooth, relatively young surfaces and degraded impact basins. The otherwise smooth surfaces of Helene and Calypso display shallow, parallel tracks often extending several kilometers; these appear to trend downslope from source regions near crater rims into low points. These tracks are locally separated by slightly higher ridges also trending down-gradient. They record mass transport over surprisingly long distances on these tiny (~30 km diameter) satellites. Some of the flows are slightly convex in cross section, suggesting deep-seated mass transport. We model these flows as glacier-like flows derived from degradation of crater rims. The rheological properties and speed of emplacement (rapid to very slow) of these flows is uncertain. Saucer-like depressions stand in positive, mesa-like relief on these satellites, which we interpret to be the floors of highly degraded impact craters, implying long-term mass loss from the satellites.