Volcanism and igneous processes in small icy satellites

Abstract

The small saturnian satellites exhibit a remarkable diversity of surficial features including many which appear to be a consequence of internal activity: 'wispy' terrain, linear troughs, and terrains displaying large gradations in crater density. I argue here that the most likely cause of endogenic processes in these bodies is the igneous activity associated with a low melting point NH_3–H_2O magma, a possibility first pointed out by Lewis. Radiogenic heating probably suffices to provide the necessary melting in Tethys, Dione, Rhea and lapetus whereas tidal heating is needed for Enceladus and possibly Mimas. Migration of large fluid-filled cracks is likely (as in Weertman's theory for water-filled crevasses in glaciers), leading to surface flooding. If clathrates are present, as first suggested by Miller, then pyroclast-forming explosive events can occur at a near-surface intrusive contact between magma and one or more of the methane, nitrogen and argon clathrates.