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N. G. Barlow (U. Central FL)
The "Catalog of Large Martian Impact Craters" currently is being revised with new data from the Mars Global Surveyor (MGS) mission . One of the new pieces of information being incorporated into the Catalog is a measurement of the maximum extent of the ejecta layers surrounding most fresh martian impact craters. The ratio of the maximum ejecta length to crater radius is called the ejecta mobility ratio and is generally believed to provide information about the viscosity of the material emplaced in the layered deposits. Previous studies by Mouginis-Mark  and Costard  suggest that ejecta mobility correlates with latitude, elevation, and ejecta type. We are utilzing the new information from MGS MOC, MOLA, and TES to re-evaluate the effect of latitude, elevation, terrain type, terrain age, composition, and terrain roughness on the radial extent of the ejecta deposits. Our eventual goal is to determine how terrain characteristics, particularly the presence of subsurface volatiles, affect the formation and emplacement of the layered ejecta morphologies. Currently our analysis is complete for the northern plains regions of Mars. We have largely completed measurements of ejecta length surrounding craters in the heavily cratered highlands and have just initiated the analysis for these regions. Our preliminary analysis has led to the following results for the northern plains: (1) We find no statistical differences in average ejecta mobility ratios for craters superposed on different types of plains. (2) The average ejecta mobility ratio of single layer craters typically has a value lying between the ejecta mobility ratios of the double layer inner and outer layers. (3) Layered ejecta deposits closer to the equator tend to have lower ejecta mobility ratios than those deposits found at higher latitudes, consistent with the earlier findings of . The results of our analysis for the heavily cratered highlands will be presented at the conference.
REFERENCES:  Barlow N. G., LPSC XXXI, Abstract #1682, 2000.  Mouginis-Mark P., JGR, 84, 8011-8022, 1979.  Costard F., Earth Moon and Planets, 45, 265-290, 1989.
ACKNOWLEDGEMENTS: This work is funded by the NASA Mars Data Analysis Program.
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