HR: 14:55h
AN: P33B-04    [Abstracts]
TI: The Unique Characteristics of Double Layered Ejecta Craters on Mars
AU: * Mouginis-Mark, P J
EM: pmm@higp.hawaii.edu
AF: University of Hawaii, Hawaii Institute Geophysics and Planetology, 1680 East-West Road, POST rm. #504, Honolulu, HI 96822 United States
AU: Boyce, J M
EM: boyce@higp.hawaii.edu
AF: University of Hawaii, Hawaii Institute Geophysics and Planetology, 1680 East-West Road, POST rm. #504, Honolulu, HI 96822 United States
AB: THEMIS VIS images reveal several unique characteristics of double layered ejecta (DLE) craters on Mars that suggest a strikingly different mode of formation from single layered ejecta (SLE) or multi-layered ejecta (MLE) craters. DLE craters are typically 15 to 25 km in diameter and differ from the other types of Martian craters in the following ways: (1) DLE craters lack secondary craters; (2) ejecta layers of DLE craters lack distal ramparts; (3) flow features within the outer layer of DLE craters suggest a very low emplacement velocity; and (4) radial striations exist only within DLE ejecta, and that these striations cross both the inner and outer ejecta layers. The interior morphology of DLE is also less complex than SLE or MLE layered ejecta craters; DLE craters lack wall terraces and, where present, have only simple central peaks. Previous morphologic analyses of DLE craters proposed that they might have formed in the volatile-rich sediments that are believed to infill areas such as Utopia, Arcadia and Acidalia Planitiae. But our inspection of the THEMIS VIS data set confirms the Viking-based results of Barlow and Perez (JGR-Planets, vol. 108 (E8), doi 10.1029/2002JE002036, 2003) that DLE craters are not uniquely located in the northern plains. We find that DLE craters with nearly identical morphologies also occur within the highlands of Mars, including Hesperia Planum, Icaria Planum, Arabia Terra, Noachis Terra, and Terra Sirenum. A few examples of DLE craters are found at a range of elevations between -5.8 km to +2.7 km relative to the MOLA datum, and within two latitudes belts between 23$\deg$ to 52$\deg$N, and between 29$\deg$ to 46$\deg$S. Thus some other mode of formation apart from impact into volatile-rich sediments of the northern plains needs to be identified. Through our on-going characterization of DLE craters with THEMIS VIS data, we hope to identify the attributes of these craters to help identify their unique mode of formation.
DE: 5400 PLANETOLOGY: SOLID SURFACE PLANETS
DE: 5420 Impact phenomena (includes cratering)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting