37th DPS Meeting, 4-9 September 2005
Session 63 Galilean Satellites
Oral, Friday, September 9, 2005, 9:00-10:30am, Law LG19

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[63.05] Cycloidal cracks on Europa: Improved propagation parameters and rotation implications

A. R. Sarid, T. A. Hurford, R. Greenberg (Univ. of AZ - LPL)

Cycloidal crack patterns on Europa are generated by tides induced by orbital eccentricity, which in turn is driven by the Laplace orbital resonance (Hoppa \emph{et al.}, \emph{Science}, \textbf{285}:1899-1902, 1999). Their shapes record the location of their formation, as well as the parameters of crack formation. Hoppa \emph{et al.} modeled each cycloid chain using a fixed set of material parameters to match the general shape of the observed features, but the details often did not fit. We now allow material parameters to vary for each arc of an observed cycloid. This freedom allows us to better fit the observed pattern, but does not allow so much freedom as to make the fit non-unique. In general, minimal variation of model parameters between the arcs of a cycloid chain results in greatly improved fits. Furthermore, accounting for stress accumulated during non-synchronous rotation, in addition to diurnal stress, allows even better fits.

Hoppa \emph{et al.} (\emph{Icarus}, \textbf{153}: 208-213, 2001) showed how modeling cycloid formation can indicate the frequency of cracking relative to the non-synchronous rotation period, e.g. they showed that three recent cycloids had to have formed in different periods of non-synchronous rotation. Our work better constrains the location where each cycloid must have formed. It confirms the finding that only a few cracks are formed per cycle of non-synchronous rotation, probably because cracking relieves built up stress until further substantial rotation occurs. On Europa, geologic features are directly linked to orbital and rotational dynamics (Greenberg, Europa, the Ocean Moon, Springer -Praxis, 2005).

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Bulletin of the American Astronomical Society, 37 #3
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