HR: 15:10h
AN: P23D-07    [Abstracts]
TI: New Insights on Ejecta Emplacement at Martian Impact Craters from HiRISE Images
AU: * Garbeil, H
EM: harold@higp.hawaii.edu
AF: HIGP/SOEST Univ. Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AU: Mouginis-Mark, P J
EM: pmm@higp.hawaii.edu
AF: HIGP/SOEST Univ. Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AU: Boyce, J M
EM: jboyce@higp.hawaii.edu
AF: HIGP/SOEST Univ. Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AB: New insights into the process of fluidized ejecta emplacement for impact craters on Mars are being derived from the analysis of the publicly-released HiRISE images. Fresh imaged craters have diameters from 1.1 km (Winslow crater) to 29.0 km (Tooting crater), and formed on a variety of target materials including Amazonian-age lava flows, Chryse Planitia, the S. Highlands, and the flanks of the Tharsis volcanoes. These data help to resolve some of the long-standing issues pertaining to the fluidization of single layered ejecta (SLE), double-layered ejecta (DLE) and multi-layered ejecta (MLE) craters on Mars. For example, at a SLE crater in the S. highlands, we see a wide range of polygonal deposits on top of the ejecta layer that are absent from the surroundings, suggestive of desiccation of a previously wet ejecta layer. Kilometer-long flows, either of impact melt or of mud, have been identified on the outer rims of both Zumba (a SLE crater) and Tooting (a MLE crater). Also at Tooting crater, we see numerous 15 to 20 m diameter pits concentrated on the up-slope sides of the distal ramparts. These pits formed in broadly linear chains, and may be related to the loss of volatiles as the ejecta came to a rest to form the rampart. In a few rare places at Tooting crater, we have found valleys on the outer scarps of the ramparts, suggestive of dewatering of the ejecta once it came to rest. The idea that recent impacts within the S. hemisphere were associated with fragmented targets is not supported by an unnamed crater (at 49.3^oS, 18.5^oE) that displays numerous angular boulders as much as 20 m in diameter on top of the ejecta layers. A fresh 6 km diameter MLE crater in Chryse Planitia (at 26.1^oN, 316.7^oE) shows that individual ejecta layers are more numerous than had previously been identified from THEMIS VIS images; these layers display considerable diversity in the number and spatial distribution of pits and are suggestive of different volatile contents and/or resistance to erosion of the layers.
DE: 5420 Impact phenomena, cratering (6022, 8136)
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting