Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p11b0115g&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P11B-0115
Mathematics
Logic
6218 Jovian Satellites, 6221 Europa, 8010 Fractures And Faults
Scientific paper
The surface of Europa, Jupiter's fourth largest moon, consists of an intensely fractured ice shell overlying a proposed ocean of liquid water. Compelling evidence for a floating ice shell comes from the presence of arcuate cracks (cycloids) unique to Europa. Cycloids consist of curved segments linked together at cusps. Crack growth is strongly controlled by rotating diurnal stresses caused by oscillating tidal bulges beneath the ice but the long-term stress due to nonsynchronous rotation (NSR) of the ice shell also likely affects the overall distribution and patterns of cycloidal features. Cycloids are linked into chains 100s - 1000s km long and are observed at a variety of orientations in nearly every imaged region of Europa. While geologic mapping has revealed cycloids are geologically recent, relative age sequences documenting multiple periods of cycloid growth are needed to observe changes in cycloid characteristics (i.e., orientation, morphology) over time. Using age sequences determined through cross-cutting relationships, and conventional means of interpreting NSR based on a consistent rotation of fracture orientations through time, we have estimated the amount of NSR that occurred purely since the onset of cycloid development in this region. The E15RegMap01 mosaic, located in the northern hemisphere, spans latitudes 19 to 62°N and longitudes 212 to 233°. Twenty-two cycloids have been identified in the mosaic, 14 of which could be fitted into a relative age sequence based on cross-cutting relationships. Consistent with results of previous NSR studies in the northern hemisphere, cycloid chain orientations in this region have generally rotated in a clockwise sense through time. Cycloid segments are defined by double ridges and cycloid cusps are either simple (one splay) or complex (multiple splays) but do not appear to show a preferential pattern through time. Preliminary results show that at least 450° of NSR occurred between the formation of the oldest and youngest cycloids studied. Previous studies have constrained 1 NSR period (i.e., 360° rotation of the ice shell relative to the satellite interior) to be between 12,000 and 240,000 years. Using those estimates and our preliminary results, the duration of cycloid development in this region has been constrained to between 15,000 and 300,000 years.
Groenleer Julie M.
Kattenhorn Simon A.
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