Mobilization of cryogenic ice in outer Solar System satellites

Abstract

Voyager images of the uranian satellites show a diversity of geological features, including clear evidence for the ‘softening’ and mobilization of ice on Miranda and Ariel. Some of these features are similar to those seen on jovian and saturnian satellites, where the mobile material is believed to be water or a water–ammonia mixture. However, the extremely low temperatures and probable unavailability of large energy sources within the uranian satellites lead us to consider flow mechanisms that operate at very low temperature (T ≤ 100 K). We propose here a form of pressure-solution creep, in which very fine-grained water ice or clathrate hydrate is mobilized by a small amount of intergranular cryogenic fluid (CH_4, CO or N_2). Viscosities as low as 10^(12) P are possible for a limited time, sufficient to allow flooding of rift valleys and perhaps even substantial lateral flows (glaciers).