HELLAS BASIN RIM EROSION: A QUANTITATIVE APPROACH

Hellas Basin, Mars, is one of the largest multi-ringed basins in the solar system, with a diameter of approximately 2300 km and a present depth of almost 9 km. Formed during the heavy bombardment period of the Noachian, the crater is relatively well preserved, although aeolian, fluvial and volcanic processes have irregularly modified this southern highlands region since its formation.

Using data from both the Mars Orbiter Laser Altimeter (MOLA) and Mars Odyssey Thermal Emission Imaging System (THEMIS), we are able to quantify the amount of material that has been eroded from the inner rim of Hellas Basin. We define the inner rim of the basin as beginning at the -5000 m elevation contour (the approximate boundary between the basin floor and the rim) and continuing radially outward a distance of 1200 km. Likely, much of the material eroded from this region of the crater rim was subsequently deposited onto the basin floor. Using the relatively narrow and steeply sloped northwestern region of the rim as a proxy for the original, pristine rim morphology, we calculate that approximately 1.16×10⁷ km³ of material has been eroded from the inner rim. This volume of material is equivalent to a layer 4.3 km in thickness on the basin floor, as defined as the area within the -5000 m topographic contour. This value, although likely conservative, coincides with several recent studies [e.g., Tanaka et al (2002), Moore and Wilhelms (2001), Rogeiro et al. (2003), Wichman and Schultz (1989)] which estimate the Hellas basin floor deposits to have thicknesses ranging from 0 km to > 5 km. Additionally, the differential degradation of the impact craters within the inner rim of Hellas Basin suggests a decreasing erosional efficiency with increasing distance from the basin floor.