"Topography and Extension on Europa"

Francis Nimmo

University of California- Los Angeles

Joint Astronomy / Earth & Planetary Science Colloquium
Sponsored by CIPS - Center for Integrative Planetary Science

4:10 PM

Colloquium Tea in Advance at 3:30 pm - 661 Campbell Hall

The manner in which a body supports topography tells us about its near-surface properties. For Europe, the most important property is the thickness of the solid ice shell, because it controls interactions between the surface and the interior, and constrains the amount of tidal heating.

Apparently flexural features on Europa may be used to infer the rigidity of the ice shell, and thus the total ice shell thickness. The thickness thus derived is ~20km, similar to independent estimates based on crater studies and tidal dissipation calculations. Such a shell thickness makes contact between the surface and the underlying ocean unlikely.

Flexure does not appear to be a major cause of positive topography in bands, extensional features similar to mid-ocean ridges on Earth. Lateral shell thickness variations cannot maintain topography over geological timescales. Lateral density variations are a more likely cause of positive topography. These density variations could be caused by variations in either porosity or salt content. The latter hypothesis suggests compositional convection may be important, and could help to explain other puzzling surface features, such as the roughly circular lenticulae.