Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p21b0534m&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P21B-0534
Mathematics
Logic
5400 Planetary Sciences: Solid Surface Planets, 5450 Orbital And Rotational Dynamics (1221), 5455 Origin And Evolution, 5475 Tectonics (8149), 6280 Saturnian Satellites
Scientific paper
We find analytic solutions for the stresses associated with distortions of biaxial or triaxial planetary figures. Distortions of biaxial figures may be driven by variations in rotation rate, rotation axis orientation, or the combination of both. Distortions of triaxial figures may be driven by the same mechanisms and/or variations in tidal axis orientation for tidally deformed satellites. While the magnitude of the resulting stresses depends on the adopted elastic and physical parameters, the expected tectonic pattern is independent of these parameters for these mechanisms. We consider the tectonic pattern on Saturn's moon Enceladus. The global scale tectonic pattern on this satellite has been interpreted as due to a rotation rate increase (Porco et al. 2006), perhaps due to a suitably oriented impact. In this scenario, the flattening increases, forcing the tidal bulge to expand and the polar regions to contract. We show that the observed tectonic pattern is more easily explained by a large reorientation (~90°) of the rotation axis roughly around the tidal axis, than by spin-up. In the spin-up scenario, extension occurs centred on the sub- and anti-Saturnian points and strike-slip faulting centered on the leading and trailing hemispheres. In the reorientation scenario, these patterns are reversed, and are more consistent with the available geological observations (Kargel and Pozio 1996, Porco et al. 2006, Helfenstein et al. 2007). Furthermore, the latitude of the predicted polewards transition to compressional stresses is comparable to that of the observed south polar terrain margin. Reorientation of ~90° may be driven by mass redistribution associated with an internal load (Nimmo & Pappalardo 2006), ice shell thickness variations (Ojakangas and Stevenson 1989), or an equatorial large impact (Melosh 1975). Given Enceladus' orbital evolution constraints, the effect of despinning due to tidal disspation on the predicted tectonic pattern is negligible.
Matsuyama Isamu
Nimmo Francis
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