Mathematics – Logic
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.6404s&link_type=abstract
American Astronomical Society, DPS meeting #38, #64.04; Bulletin of the American Astronomical Society, Vol. 38, p.612
Mathematics
Logic
1
Scientific paper
Arcuate cracks, called cycloids, are ubiquitous on the surface of Europa and form as the result of diurnally-varying tidal stress. Modeling of cycloids based on tidal stress has provided evidence for non-synchronous rotation of Europa and helped to constrain its rotation rate (Hoppa et al., Science, 285:1899-1902, 1999). While fits of cycloids have improved over time, the diurnal stress model still cannot reproduce certain features, even when stress accumulated during non-synchronous rotation is taken into account. In particular, observed cycloids that are near to or crossing the equator have not been modeled successfully in previous studies.
Recently it has been suggested that Europa has a forced obliquity of order 0.1º (Bills, Icarus, 175(1):233-247, 2005). Hurford et al. investigated the effects of obliquity on the stress field and generated global maps of hypothetical cycloids (LPSC abstract #13.03, 2006). They found that several of the observed attributes of the global cycloidal crack pattern, which were previously not reproducible, are natural results of stress from a small amount of obliquity ( 0.1º). Here, we reexamine specific cycloids that lie near or across the equator. Previously we were unable to model these features, but inclusion of the stresses resulting from Europa's obliquity has allowed us to finally reproduce these cycloids. Our preliminary results indicate that 0.25º of obliquity is needed to fit these features. In addition, non-synchronous rotation is still required to explain how the cycloids have migrated from their formation longitudes to their current locations. Our results provide the first geologic evidence for a finite obliquity of Europa and confirm the likelihood of slow non-synchronous rotation. In order to understand the surface history of Europa, the effects of obliquity must be taken into account. When modeling cycloids, specifically, including such effects may lead to a more accurate determination of the non-synchronous rotation rate.
Greenberg Richard
Hurford Terry A.
Sarid Alyssa R.
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