Mathematics – Logic
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.6607s&link_type=abstract
American Astronomical Society, DPS meeting #41, #66.07
Mathematics
Logic
Scientific paper
The mismatch between observations of strike-slip faults on Europa and the predictions from a tidal formation model, dubbed tidal walking (Hoppa et al., 1999), imply that Europa's surface underwent polar wander of 30°. However, the model only included the tidal effects of Europa's forced eccentricity. Interactions with Io and Ganymede may force Europa's obliquity to be at least 0.1°, and it could be much larger if the surface is mechanically decoupled from the interior by a subsurface ocean. In addition, the value of the obliquity and the direction of the spin pole can change over geologically relevant timescales. In a previous study, we showed that by incorporating obliquity into tidal models of cycloid formation, fits to observed cycloids greatly improve; fits indicate an obliquity of at least 1° with variable spin pole directions, consistent with expectations for a mechanically decoupled ice shell.
In this work, we determine the sense of slip (right or left lateral) along faults resulting from a tidal walking model that incorporates obliquity into the tidal stress calculation and compare these predictions to observations of strike-slip faults. These observations include the locations, azimuths, and slip senses of almost 200 faults identified in a previous survey (Sarid et al., 2002) that used Galileo 250 m/pix resolution regional mapping imagery. These are the same observations that were previously interpreted as evidence of polar wander. We find that an obliquity of 1.25° can account for the sense of slip along all the observed strike-slip faults whereas even 40° of polar wander still cannot match the slip along several features. Longitude migration, attributed to non-synchronous rotation of the icy shell, is required in either case to fit the majority of features. Measuring Europa's current obliquity and spin pole direction would be a useful goal of a future Europa mission.
Hurford Terry A.
Manga Michael
Sarid Alyssa R.
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