HR: 0800h
AN: P41A-0890    [Abstracts]
TI: The Latest Hits: Investigating the Recent Cratering Record on Mars
AU: * Calef, F J
EM: fred@gi.alaska.edu
AF: Geophysical Institute, 903 Koyukuk Drive Univ. of Alaska, Fairbanks, Fairbanks, AK 99775-7320 United States
AU: Sharpton, V B
EM: buck.sharpton@gi.alaska.edu
AF: Geophysical Institute, 903 Koyukuk Drive Univ. of Alaska, Fairbanks, Fairbanks, AK 99775-7320 United States
AU: Morell, K D
EM: kmorell@alum.wellesley.edu
AF: Penn State University, Dept. of Geosciences 503 Deike Building, University Park, PA 16802 United States
AB: We have initiated a preliminary study of sub-kilometer craters exhibiting distinct ejecta within 160 MOC-NA images located between $20\deg$W - $120\deg$W longitude and $30\deg$S - $90\deg$N latitude as well as several on the flanks of Olympus Mons. Most of the craters showed distinctly rayed ejecta (49%), while 27% (96) displayed circular, 12% (43) lobate, and 10% (36) exhibited a combination of several blanket types. Two-thirds of the craters showed dark ejecta (64.7%, 230 craters) compared to the surrounding target surface. No preferred elevation was evident from the data, nor was any surface-age preference detected. Crater counts on this population indicate that ejecta retention is a strong function of crater diameter for craters less than ~200m; above this range, the slope of the size-frequency distribution (D-n) approaches the Hartmann isochron of ~1Ma, indicating that ejecta retention is a reasonably reliable indicator of recent crater formation. The low slope of the D-n plot below 200m reveals that surface activity is extremely efficient at obscuring the ejecta around the smallest craters on Mars. This seems reasonable that the ejecta deposits of increasingly smaller craters are themselves thinner and finer grained and are therefore more easily removed or obscured by aeolian activity.
DE: 5415 Erosion and weathering
DE: 5420 Impact phenomena (includes cratering)
DE: 5499 General or miscellaneous
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting