Crater shape evolution with latitude in Terra Cimmeria, Mars - implications for climate

Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online's data policy on reuse of materials please consult the policies page. Introduction: We have used topographic data from the High Resolution Stereo Camera (HRSC) in the Terra Cimmeria region on Mars running from latitudes 25 to 50°S (Fig. 1) to investigate the effects of climate on changing crater form. The Mars Orbiter Laser Altimeter (MOLA) global topographic data have already revealed that steep slopes are more prevalent near the equator and that gradual softening of topography occurs towards the poles [1] due to deposi-tion of a volatile-rich µmantling ¶ material [2]. We have taken advantage of the higher resolution of the HRSC data (30-90 m/pix in the 5 HRSC DEMs used compared to ~400 m/pix for MOLA) to investigate whether similar trends can be seen in crater shape. Approach: We used crater survey GT57633 [3] as a basis for our extended crater map in this region. For each crater we delineated four zones: north-, southeast stand west-facing (Fig. 2). Within each zone we calculated the curvature of the crater wall, its mean slope and its maximum slope. The process is illustrated in Fig. 2. This was achieved by averaging all data points in 100m distance intervals from the centre-point. The maximum and mean slopes were calculated from these profiles. For each profile the distance from the centre-point was normalized by the crater radius and the height was normalized by overall crater depth. A power-law of the form y = Ax n was fitted to the normalized data. The exponent n of the power law describes the curvature of the crater walls, low values being bowl-shaped and high values being flat-bottomed, or U-shaped. We also performed a rudimentary classification of craters into µyoung ¶, those with visible ejecta and sharp rim, and otherwise µold ¶. We compared results from our 30 and 90 m HRSC elevation models, to those from MOLA gridded data at ~400m resolution. Results: We measured 433 craters ranging from 1 to 64 km in diameter in the region. The exponent of the power law (n) increases towards higher latitudes and this is more marked for south-facing slopes. This trend is almost undetectable in MOLA data. This implies craters become more µU ¶ shaped, or flat-bottomed rather than bowl-shaped towards the …