The Mechanism for Forming Martian Rampart Craters: Clues from Crater Morphometry
Abstract
Many large craters on the martian surface have ejecta blankets that terminate with a pronounced lobate ridge. These rampart craters represent features unique to Mars, and their morphology suggests that their ejecta was emplaced as a highly mobile fluid instead of ballistically. High velocity experiments into mud have duplicated many of the common morphologic characteristics of rampart craters supporting this hypothesis. However, additional experiments performed at a variety of atmospheric pressures have also been able to duplicate aspects of rampart crater morphology These results suggest that rampart craters form as the result of a low pressure atmosphere. Obviously the presence of ice or water would have an effect on the target properties (i.e., material strength) of the martian substrate, which should also influence the overall crater morphometry, thus allowing us to test these competing hypotheses. In this study we used the photoclinometric algorithm developed by Davis and Soderblom and written for the Planetary Image Cartography System to determined the shape of over 300 fresh lunar-like or rampart impact craters at a variety of diameters (3 to 80 km). Because it is probable that Ethology would also effect the strength of the target material, we confined our study to craters formed in the dissected unit of the Highland Plateau (Npld) as defined by the 1:15M-scale geologic mappers and interpretable to the scale of our images. In addition we confined our study to +30 degrees to omit variations in crater morphology seen at higher latitudes. The images used were radiometrically-calibrated (red and minus-blue filter), moderate resolution (~200 m/pixel) obtained by the Viking orbiters. Our initial results show that there is a slight difference in morphometric relations between fresh lunar-like and rampart craters, supporting the hypothesis that the unique morphology of rampart crater ejecta results from the incorporation of volatile materials contained in the target substrate.
- Publication:
-
Lunar and Planetary Science Conference
- Pub Date:
- March 1996
- Bibcode:
- 1996LPI....27..263C
- Keywords:
-
- CRATERS: RAMPART;
- MARS: HIGHLANDS;
- MORPHOMETRY: CRATER