Statistics – Methodology
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.p53b1242s&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P53B-1242
Statistics
Methodology
5450 Orbital And Rotational Dynamics (1221), 5475 Tectonics (8149), 6221 Europa
Scientific paper
Cycloids are made up of linked arcuate segments and were observed in both Voyager and Galileo imagery. It has been proposed that cycloids are fractures that propagate in response to the tidal stress field, which changes throughout each orbit due to Europa's eccentricity. Several studies have tested tidal models by generating cycloidal features and comparing them to actual cycloids, resulting in compelling evidence for non-synchronous rotation. Also, recent modeling of cycloids in equatorial regions has shown that the obliquity of Europa is large enough to affect the formation of surface features. In addition to constraining the orbital and rotational parameters that control Europa's tidal stress field, modeling of cycloidal fractures can provide constraints on the mechanical properties of the ice shell. Despite the successes of cycloid modeling, the methodology for generating cycloids and comparing them with actual data could be greatly improved and more widely applied. Only five cycloids have been modeled although dozens of global-scale features can be identified in the Galileo images. And although equatorial cycloids provide the best constraints on the amount of obliquity and direction of the spin pole, only one cycloid in this region has been successfully modeled, mostly due to the increased parameter space and lack of symmetry in the stress field. Searching for best fits by hand is no longer feasible, especially for the large number of cycloids needed to precisely constrain Europa's orbital and rotational parameters. In addition, past cycloid modeling has not relied on a quantitative measure of goodness of fit when matching hypothetical cycloids to the observed features. While this approach may have been satisfactory for early work, as fits improve, it becomes increasingly important to have a consistent and quantitative measure with which to evaluate modeled cycloids. Moreover, a quantitative measure of misfit can be translated into uncertainties for model parameters. We are currently developing a new method of cycloid modeling that combines the standard tidal model (including obliquity) with an automated and quantitative fitting program and a Markov Chain Monte Carlo algorithm to search the parameter space. Our preliminary work has shown that this method is effective when applied to a synthetic crack; the algorithm does indeed "find" the parameters with which the crack was generated. Our ongoing work involves mapping and modeling large-scale equatorial cycloids, using this upgraded method, in order to constrain the amount of obliquity, direction of the spin pole, non-synchronous rotation rate, and amount of stress generated by non-synchronous rotation.
Huff Eric M.
Hurford Terry
Manga Michael
Sarid Alyssa Rose
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