HR: 17:45h
AN: C12C-08 INVITED     [PDF]
TI: Icy Satellites: Perpetual Permafrost
AU: * Pappalardo, R T
EM: robert.pappalardo@colorado.edu
AF: LASP, University of Colorado, Box 392, Boulder, CO 80309
AU: Moore, J M
EM: jeff.moore@nasa.gov
AF: Ames Research Center, MS 245-3, Moffett Field, CA 94035 United States
AB: The ice-rich moons of the outer solar system are worlds of perpetual permafrost. By analogy to the terrestrial roles of silicates and water ice, surface materials of these worlds commonly consist of components that are respectively refractory and volatile at local environmental conditions. We consider the physical properties, volatile components, and geomorphological characteristics of outer planet satellite surfaces and shallow regoliths as analogs to permafrost environments. Near-surface temperatures of ~40 to 165 K preclude melting of water-ice, except where endogenic activity has increased surface temperatures locally. However, water and/or more volatile ices can be transported in the vapor phase, and can liquefy in the deeper subsurface. In the water-ice-poor regolith of Io, SO2 and possibly H2S are volatile ices that can be transported in the vapor phase and can liquefy at depth, resulting in degradation and local collapse of the ground surface. Sublimation degradation is especially evident in images of Callisto, where slow diffusive loss of CO2 is the likely erosive agent. On Neptune's large moon Triton, nitrogen plays the role of a permafrost volatile, near its melting temperature in a regolith of more refractory ices. Most large icy satellites probably have water-rich subsurface oceans, and it has been proposed that Europa's subsurface ocean might sustain life. Frigid surface temperatures and severe charged particle radiation preclude near-surface metabolism, but organisms could potentially survive within deeper regions and local upwelling plumes that approach the ice melting temperature.
DE: 6218 Jovian satellites
SC: Cryosphere [C]
MN: 2003 Fall Meeting