A Detailed Comparison of Europa's Global Lineaments to Non-synchronous Rotation Stresses

Details A Detailed Comparison of Europa's Global Lineaments to Non-synchronous Rotation Stresses A Detailed Comparison of Europa's Global Lineaments to Non-synchronous Rotation Stresses

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p51e1166s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P51E-1166

Physics

[5475] Planetary Sciences: Solid Surface Planets / Tectonics, [6221] Planetary Sciences: Solar System Objects / Europa

Scientific paper

The geographic characteristics of Europa's global-scale lineaments, which are widely presumed to be extensional tectonic features, have been cited as evidence that the satellite's ice shell has experienced non-synchronous rotation (NSR). It has also been suggested that the shell has undergone one or more episodes of true polar wander (TPW). We assume that stress due to NSR is dominant in the shell and that the ice fails via tensile fracture, and then measure how well each lineament fits the NSR stress field as a function of westward translation (b). This allows the reconstruction of an apparent history of lineament formation activity, H(b), with b acting as a proxy for time. We find that it is not possible to confidently attribute the geography of any individual lineament to the NSR stresses, but that there are properties of ensembles of features which are potentially diagnostic of NSR. These include (1) their distribution in latitude, (2) the distribution of their orientations in the equatorial regions, and (3) the non-uniformity of H(b), which we quantify using the relative mean difference (RMD) of H(b): RMD(H(b)) ≡ ∑(|H(b1)-H(b2)|) /for b1,b2 ∈ [0°,180°) The ensemble of 661 features we mapped distinguishes itself significantly by displaying a highly non-uniform H(b), with a concentrated peak in activity at b=30°. The localization of activity in rotational space suggests that less than one full shell rotation is recorded by the global lineaments, and may be explained by either (1) a steady-state lineament formation process in which new features become progressively more visible with time while active and then slowly succumb to resurfacing once quiescent, or (2) by a transient lineament formation event, after which NSR of the shell continues without generating further lineaments. If the shell responds viscously to the NSR forcing, some or all of the peak's displacement from b=0° may result from a phase lag between the tidal potential and the induced stresses. We also find that the current pole nearly maximizes the RMD of H(b), suggesting that the global lineaments can only be interpreted as evidence of NSR about the current pole, and that if TPW has occurred, it must have taken place prior to the creation of the prominent large-scale linear features we see today. Gray histogram shows RMD(H(b)) for our map transformed to 1000 uniformly distributed paleopoles. Black histogram shows distribution for 50000 longitudinally randomized resamplings of the map.

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