Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p21c..06s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P21C-06
Mathematics
Logic
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5421] Planetary Sciences: Solid Surface Planets / Interactions With Particles And Fields, [5465] Planetary Sciences: Solid Surface Planets / Rings And Dust, [5475] Planetary Sciences: Solid Surface Planets / Tectonics
Scientific paper
The first (Cassini orbiter-based) global mapping, color and topographic maps of the innermost of Saturn’s classical midsize icy moons have radically changed our Voyager-based perspectives. Geologically, the 125x145-km-wide, ~12-km-deep Herschel impact crater still dominates the moon. Recent observations confirm this crater in essentially unrelaxed, and is not ancient (possibly less than 1 Gyr). The crater population in the region antipodal to Herschel is now seen to have depths less than half that of normal craters and a disorganized topographic signature. This is provisionally interpreted as evidence for seismic disruption similar to that seen for Caloris Basin on Mercury. A global network of grooves (first detected by Voyager) has been mapped. These are 2 to 3 km deep and appear to be located preferentially in equatorial regions (pending north polar mapping). Many of these grooves may be radial to Herschel although they could also represent extensional cracks due to orbital contraction. The colors of Mimas are dominated E-ring dust deposition on the trailing hemisphere and by the recently discovered (Schenk et al., 2009) equatorial lens extending across the entire leading hemisphere. This lens is distinctly bright in the UV (~0l34 micron) and thus bluish in color and extends from ~30 S to 30 N at its maximum width in the center of the hemisphere. This pattern is very similar to that observed (originally by Voyager) on Tethys. Although the Mimas Equatorial Band (MEB) extends further north in latitude, it is actually narrower when measured on the ground. Both features match the surface patterns expected for irradiation of the surface by incident very energetic MeV electrons that drift in a direction opposite to the plasma flow. These electrons spiral in and preferentially impact the leading hemispheres. Their flux is strongest in the inner Saturn system, explaining the absence of banding on the more distant moons. Enceladus itself is shielded by the densest part of the E-ring, in which it resides, and by the ongoing deposition of plume fallout. The mechanism of surface alteration is uncertain but the recent detection by CIRS (Spencer et al., 2010) of a temperature anomaly in spatial association with the bluish MEB indicates that the surface microstructure is being altered in such a way as to significantly change both the UV signature and the thermal inertia. The bands on both Tethys and Mimas thus record the impact of major components of Saturn’s magnetosphere and help confirm their behavior.
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