Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p53b1235v&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P53B-1235
Physics
1240 Satellite Geodesy: Results (6929, 7215, 7230, 7240), 5770 Tidal Forces, 6035 Orbital And Rotational Dynamics, 6221 Europa
Scientific paper
As a result of rotation and tides, Europa takes a triaxial ellipsoidal form with the longest axis in the direction to Jupiter and the rotation axis as the shortest axis. The solid interior, subsurface ocean, and shell have different polar and equatorial flattenings. In the hydrostatic approximation, the internal flattening profile can be determined from the density profile of the interior structure by using Clairaut theory. We calculated interior structure models of Europa and the shape of the internal layers by using the mass, radius, and mean moment of inertia as constraints. To obtain the moment of inertia, we extended the classical Radau equation, which relates the rotational flattening of the surface to the mean moment of inertia, to include also tidal deformation. Because of the equatorial flattening of the icy shell and the solid interior, misalignment of the principal axes of the icy shell and the solid interior due to differential rotation results in gravitational coupling between both layers. We derived an analytical expression for the strength of this coupling by using an approach that has been developed for the gravitational coupling between the mantle and the solid inner core of the Earth. The shell-interior gravitational coupling implies that rotation variations (librations) of the surface of Europa cannot be studied separately from the librations of the interior. We calculated the coupled librations of the shell and solid interior for a set of models of the interior structure of Europa. The presence of an ocean is shown to increase the amplitude of libration by about 7%, depending mainly on the thickness of the icy shell. Therefore, libration observations offer the possibility of detection of a subsurface ocean in Europa and estimation of the thickness of its overlying icy shell. For very thin shells of about 1 km, our results show that the shell libration is resonantly amplified.
Hoolst Tim Van
Karatekin Ö.
Rambaux Nicolas
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