Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u21a0008m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U21A-0008
Physics
5417 Gravitational Fields (1221), 5450 Orbital And Rotational Dynamics (1221), 5455 Origin And Evolution, 5475 Tectonics (8149), 6235 Mercury
Scientific paper
We consider the effect of tidal deformation, spin-orbit resonance, non-zero eccentricity, despinning, and reorientation on the global-scale gravity, shape, and tectonic patterns of planetary bodies. Large variations of the gravity and shape coefficients from the synchronous rotation and zero eccentricity values, J2/C22=10/3 and (b-c)/(a-c)=1/4, arise due to non-synchronous rotation and non-zero eccentricity even in the absence of reorientation or despinning. Reorientation or despinning induce additional variations. As an illustration of this theory, we consider the specific example of Mercury. The large gravity coefficients estimated from the Mariner 10 flybys cannot be attributed to the Caloris basin alone since the required mass excess in this case would have caused Caloris to migrate to one of Mercury's hot poles. Similarly, a large remnant bulge due to a smaller semimajor axis and spin-orbit resonance can be dismissed since the required semimajor axis is unphysically small (< 0.1 AU). Reorientation of a large remnant bulge recording an epoch of faster rotation (without significant semimajor axis variations) can explain the large gravity coefficients. This requires initial rotation rates > 20 times the present value and a positive gravity anomaly associated with Caloris capable of driving 10-45° equatorward reorientation. The required gravity anomaly can be explained by infilling of the basin with material of thicknesses > 7 km, or an annulus of volcanic plains emplaced around the basin with annulus width ~ 1200 km and fill thicknesses > 2 km. The predicted tectonic pattern due to these despinning and reorientation scenarios and radial contraction is in good agreement with the observed lobate scarp pattern.
Matsuyama Isamu
Nimmo Francis
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