A. R. Sarid, T. A. Hurford, R. Greenberg (University of Arizona)
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.}, Science, \textbf{285}:1899-1902, 1999). Their shapes record the location of their formation. Hoppa \emph{et al.} (Icarus, \textbf{153}:208-213, 2001) exploited that information to show that three recent cycloids had to have formed in different periods of non-synchronous rotation. They modeled each cycloid chain using a fixed set of material parameters to match the general shape of the observed features, but not the details.
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, model parameters vary little between the arcs of a cycloid chain. Including stress accumulated during non-synchronous rotation, in addition to diurnal stress, improves the fits.
This work better constrains the location where each cycloid must have formed. It also 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).
Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.