Does Europa have a subsurface ocean, and how do we know?
Europa’s geological features (including bands, ridges, chaos, and multi-ringed impact structures) are indicative of warm, mobile, glacial ice at relatively shallow depths, and sometimes reaching the surface. Beneath this warm “slushy” ice could be a liquid water ocean, but it is difficult to be certain with the data that are in hand. Tidal heating is greatly aided by the presence of an ocean, so a warm near-surface is suggestive of a subsurface ocean. Also, the surface of Europa seems to have “slipped” relative to its interior in a process called “nonsynchronous rotation,” judging by the pattern of the satellite’s large-scale fractures–a subsurface ocean would greatly facilitate this. Recent work by Greg Hoppa and Randy Tufts indicates that Europa’s bizarre “cycloidal” shaped features probably owe their origin to cracking in response to tidal flexing of Europa’s icy shell on the very rapid time scale of its 3.55 day orbit; this requires large tides, best facilitated by liquid water. T
