HR: 0800h
AN: P21B-0545    [Abstracts]
TI: Impact Crater Distributions on the Saturnian Satellites From Cassini ISS Imaging - Implications for Geologic Histories and Ages
AU: * Kirchoff, M R
EM: kirchoff@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058, United States
AU: Schenk, P
EM: schenk@lpi.usra.edu
AF: Lunar and Planetary Institute, 3600 Bay Area Blvd, Houston, TX 77058, United States
AB: Although we can observe any current activity, such as the plumes on Enceladus, with the Cassini orbiter, insight into past activity on the Saturnian satellites can only be achieved (for now) through studying the impact crater distributions. Previous work by the authors (Kirchoff et al., LPSC XXXVII, #2089, 2007) has indicated that the distribution on Enceladus is particularly intriguing. This is not only because of the relatively recent resurfacing of the ridged terrain implied by the lower crater density, but also the difference of the distribution on Enceladus' heavily cratered terrain when compared to the heavily cratered terrains of Rhea, Mimas and Dione. When the crater size distribution data is plotted in a R-plot we find that Enceladus' distribution has steeper drop offs at both the small (< 2 km) and large (> 9 km) diameter range. This implies that Enceladus is "missing" smaller and larger craters when compared to Rhea, Mimas and Dione. Several hypotheses can be formulated to account for this interesting difference in the distributions. The first is simply that the heavily cratered terrain on Enceladus has been impacted by a different population than these other bodies. This idea has been presented before by several authors (e.g., Plescia & Boyce, Nature 301, 666-670, 1983), and has typically been referred to as "Population 2". Population 2 is believed to be composed of planetocentric debris created by ejecta from large impact basins such as Odysseus on Tethys. The second is that impact craters on Enceladus have been undergoing some type of endogenic modification. For example, the smallest craters could be erased by burial from plume material (Kirchoff et al., LPSC XXXVII, #2089, 2007) and larger craters by relaxation (e.g., Smith et al., LPSC XXXVII, #2237, 2007). We will test these hypotheses (and possibly formulate new ones) by analyses of the impact crater distributions on Enceladus, Dione, Rhea, Tethys, Iapetus and Phoebe. To test the endogenic hypothesis, we will also look at the spatial distribution of impact craters in the heavily cratered terrain on Enceladus and topography of the craters.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 6207 Comparative planetology
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting