Recent and fossil deposits of dark material in Martian Craters

Abstract

As a result of weathering and aeolian processes a fine-grained dark material is distributed all over the Martian surface. On crater floors it is frequently accumulated as dunes. Mobile dunes are probably built and shifted by the actual wind fields. If the dune orientation does not coincide with the actual wind fields, the dunes are assumed fossil. We present a comparison between the actual wind fields and the main orientation of the dune formation. The latter was derived from the dune morphology and wind streaks. The aim of this study is to discriminate between recent and fossil forms of dark material dunes. For the analysis, we have selected about 50 craters with occurrences of aeolian dark dunes. The data base for the craters is HRSC-Data, which provides a high spectral diversity. High resolution MOC-images are used to analyze the dune shapes. For the actual wind directions modeled wind fields from the Mars Climate Database (MCD) and wind direction data from the Mars Global Reference Atmospheric Model (MarsGRAM Ver. 2001) are used. The results of both datasets will be compared. Additionally, THEMIS nighttime infrared data are used to get information about the brightness temperature of the dune surface, which closely relates to thermal inertia. Some of the dune fields show a good correlation with the actual wind fields indicating that they might still be active. But others show different wind directions, suggesting fossil forms. This selective mobility and the analysis of the THEMIS-data indicate differences in the surface properties, e.g. consolidation of some dune surfaces.