by Francis Nimmo
University of California, Los Angeles
3-4pm
Thursday October 23, 2003
Refreshments served at 2:45pm
Munk Conference Room
Cecil and Ida M. Green Institute of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego
http://mahi.ucsd.edu/seminar/
Abstract
The manner in which a body supports topography tells us about its near-surface properties. For Europa, 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.