Ansan, V.

Conway, S. J.

Mangold, N.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsCrater shape evolution with latitude in TerraCimmeria, Mars - implications for climateConference or Workshop ItemHow to cite:Conway, S. J.; Mangold, N. and Ansan, V. (2011). Crater shape evolution with latitude in Terra Cimmeria,Mars - implications for climate. In: 42nd Lunar and Planetary Institute Science Conference, 7-11 Mar 2011, TheWoodlands, TX, USA, p. 2174.For guidance on citations see FAQs.c© 2011 The AuthorsVersion: Not SetLink(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2011/Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukCRATER SHAPE EVOLUTION WITH LATITUDE IN TERRA CIMMERIA, MARS ± IMPLICATIONS FOR CLIMATE.  S. J. Conway1, N. Mangold1 and V. Ansan1, 1LPGN, CNRS/Univ. Nantes, 44322 Nantes, France, susan.conway@univ-nantes.fr.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 effectsof climate on changing crater form. The Mars Orbiter Laser Altimeter (MOLA) global topographic data have already revealed that steep slopes are more prev-alent 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-, south-, east- and 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 illustrat-ed in Fig. 2. This was achieved by averaging all datapoints 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 = Axn 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 rudimen-tary 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 1to 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 im-plies craters become more µU¶ shaped, or flat-bottomed rather than bowl-shaped towards the pole. This trend is less marked in µyoung¶ craters. We at-tribute this to the greater infilling of craters at mid-latitudes, possibly associated with viscous flow fea-tures [4]. We have not noted any particular trend for the coefficient of the power law (A). We observed that steeper maximum slopes arefound towards the equator, as expected from previous work [1]. This trend is present in MOLA gridded data,but not as strong as for HRSC, or the MOLA profile data used by [1]. This trend is stronger for south- orpole-facing slopes (Fig. 3) and for µyoung¶ craters in the HRSC data. It is also noteworthy that the slopes measured in HRSC data are much higher than those measured from MOLA (mean of 0.07 in MOLA and 0.26 in HRSC).Mean slope shows a similar latitudinal trend to the maximum slope, but south-facing slopes and young craters are not different from the general population.Conclusions and outlook:  The trends for crater shape are clearer in HRSC data than for MOLA grid-ded data. The HRSC data can be used to study slopes of any orientation, unlike MOLA profile data, which can only be used in the N-S direction. Hence, HRSC data presents a better candidate for regional studies of topography. We have found crater shape is highly dependent on latitude, with steeper slopes and bowl-shaped forms being more common towards the equa-tor in slopes of all orientations, and particularly pole-facing ones. We intend to map gullies and viscous flow features, which are climate-related features, to assess their influence on these trends in crater form.We will also utilize landscape evolution models toevaluate the effects of different slope processes (e.g. creep, rockfall, gullying).References: [1] Kreslavsky M. A. and Head J. W. (2000) JGR, 105, 26695-26712. [2] Mustard J. F. et al. (2001) Nature, 412, 411-414. [3] Salamuniücar G. and Lonþariü S. (2008) PSS, 56, 1992-2008.  [4] Mil-liken R. E. et al. (2003) JGR Planets, 108, doi:10.1029/2002JE002005.2174.pdf42nd Lunar and Planetary Science Conference (2011)Fig. 1. Map of study area, with craters marked in yel-low, background is MOLA, and images are HRSCH0228_0000, H0241_0000, H0280_0001, H0293_0000 and H2590_0001.Fig. 2. Illustration of proceedure to extract statistics from craters. The elevation data within the blue segment highlighted in the insert graphic are plotted in grey on the graph. The black line is the avaerage slope profile for these data, from which the maximum slope is calculated. The dotted blue line is the power-law fit (un-normalized to aid display).Fig. 3. Maximum crater wall slope against latitude for S-,W-, E-and N-facing slopes. Dots are means and blue bars are one standard deviation.2174.pdf42nd Lunar and Planetary Science Conference (2011)

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

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