Time, tides and tectonics on icy satellites

In the outer solar system, we cannot use the radiometric dating techniques applied in terrestrial geology. We also lack the detailed understanding of the correspondence between crater size-frequency distributions and absolute ages that lunar samples has given us in the inner solar system. Additionally, many geologically interesting icy satellites are insufficiently cratered to yield precise relative ages. Thus we must find other ways to construct geological chronologies In this work I develop two techniques.;The first compares the linear tectonic features covering Jupiter's moon Europa to modeled tensile fractures resulting from tidal stresses due to the nonsynchronous rotation (NSR) of the satellite's decoupled, icy, lithospheric shell. The amount of shell rotation required to align a feature with the stress field resulting from NSR is used as a proxy for time. This translation is potentially convolved with a phase lag between the tidal potential and the stresses it induces, resulting from the shell's partially viscous response to the NSR forcing. The geography of individual lineaments is found to be no more consistent with NSR stresses than chance would predict, however, the ensemble of global lineaments displays a non-uniform apparent rate of lineament formation throughout the time period recorded by the surface. This non-uniformity may be explained either by steady state fracture formation, activity, quiescence and erasure, or by a transient episode of tectonics.;The second technique encodes the myriad superposition relationships evident between Europa's tectonic features as a directed graph enabling algorithmic analysis. The observed superposition relationships are generally insufficient to construct complete stratigraphic stacks, but we can calculate the degree to which they corroborate or contradict another hypothesized order of formation. We find that they tend to corroborate the hypothesis that the lineaments are tensile fractures due to prograde NSR stresses.;Together these results offer cautious support for the idea that Europa's shell rotates independently of its silicate interior, and demonstrate techniques useful in comparing tectonic features on other icy satellites to hypothesized mechanisms of formation.