DPS Meeting, Madison, October 1998
Session 22P. Mars Surface I, II
Contributed Poster Session, Monday, October 12, 1998, 3:15-4:15pm, Hall of Ideas

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[22P.09] Determining the Distribution of Subsurface H2O on Mars from Impact Crater Ejecta Morphologies

C. Perez, N. G. Barlow (U. Central Florida)

Most fresh martian impact craters are surrounded by lobate ejecta patterns emplaced by fluidization processes. Two theories exist to explain how this fluidized pattern is emplaced: (a) impact into and vaporization of subsurface volatiles, and (b) atmospheric entrainment of ejecta. Based on the observation of a diameter-latitude correlation among different ejecta morphologies by Barlow and Bradley (1990), the first theory appears dominant in the formation of the martian fluidized ejecta morphologies.

We have instituted a study to determine if longitudinal variations in ejecta morphology occur, which will provide information about the distribution of subsurface ice vs liquid water reservoirs on Mars. We have completed the analysis for 0-30N, longitude 315W westward to 180W. We used Viking Orbiter imagery with about 100 m per px resolution. We found interesting relations within the study area, suggesting that longitudinal variations in ejecta morphology do exist and likely provide inromation about subsurface properties. We found double lobe (DL) crater, although normally quite rare within our study area, make up a larger percentage of ejecta craters in 20-30N 50-90W. This area corresponds with the depositional regions of several ourflow channels, suggesting that DL craters form by impact into layered material from the river deposits. We found multiple lobe (ML) craters make up a larger percentage of ejecta craters between 0-25N, 315-10W. This corresponds to an area of heavily cratered ancient terrain and suggests that liquid water reservoirs are more prevalent here. The most common ejecta morphology is single lobe (SL). SL craters are proposed to form by impact into ice, indicating that subsurface ice is prevalent throughout our study region. Finally the radial ejecta morphology (Rd) is more common around craters in the Tharsis region, suggesting that drier material is found around the volcanoes.

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