HR: 14:10h
AN: P33B-02    [Abstracts]
TI: Comparing Styles of Crater Gradation in Gusev Crater, Meridiani Planum, and on the Earth
AU: * Grant, J A
EM: grantj@nasm.si.edu
AF: Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, 6th at Independence SW, Washington, DC 20560 United States
AB: The Mars Exploration Rovers Spirit and Opportunity investigation of impact craters yields data enabling comparisons to terrestrial craters and helps constrain the processes responsible for gradation within Gusev crater and Meridiani Planum. In Gusev, the Spirit rover has imaged variably preserved craters ranging between 1 to approximately 200 meters in diameter. These craters and their associated ejecta deposits dominate the surficial landscape, possess raised rims, and are characterized by walls sloping at angles generally less than 10 degrees. By contrast, craters explored at Meridiani Planum are between 10 and 150 m in diameter, formed into bedrock, and possess variably sloped walls that locally exceed the repose angle in Endurance crater. Comparisons between craters in Meridiani and Gusev and simple terrestrial craters provide clues to the amount and processes responsible for their gradation. For example, modification of terrestrial craters in even the most arid environments involves an appreciable water-driven component that typically leads to notched rims and disparate interior and exterior drainage networks. Drainage features evolve and eventually outpace mass wasting as wall gradients are reduced by back wasting and down slope redistribution of debris via incised debris chutes that terminate in a mix of talus and increasing alluvium. Terrestrial craters can also form an efficient trap for eolian sediments that accumulate to 10's of meters in Roter Kamm crater in Namibia, but still do not mask features diagnostic of gradation by water. None of the Martian craters display landforms diagnostic of significant modification by water. Moreover, the absence of debris chutes or obvious talus along crater walls in Gusev coupled with generally well preserved ejecta deposits implies modification by mass wasting is limited and accompanied by local deflation and eolian deposition typically less than 1-2 meters. In Meridiani, some craters appear relatively pristine (Fram) whereas others are more modified by mass wasting and back wasting of the wall (Endurance) and significant deflation of ejecta and eolian infilling (Eagle and Endurance). Differences in gradational signatures associated with these Martian and terrestrial craters are due in part to the limited role played by water in post-Noachian gradation of the Martian craters. Although water may have contributed to local redistribution of fragments to form pavements or other small scale landforms, comparison with terrestrial craters and the predominance of eolian and mass wasting landforms demonstrates water was subordinate in crater modification on Mars.
DE: 5420 Impact phenomena (includes cratering)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting