Inlet valleys that cut into crater rims on Mars.

Post contributed by Emily Bamber (PhD Candidate), Jackson School of Geoscience, University of Texas at Austin

Impact craters are a common feature of the surface of Mars and other planetary bodies. Impact craters are formed by the force of an asteroid or comet colliding with the surface of a planet. This collision excavates a bowl-shaped depression and causes uplift, deformation and deposition of excavated material to form a crater rim, which can rise hundreds of meters above the surroundings (for a crater on the scale of tens of kilometers in diameter). However, some of Mars’ impact craters stand out from their counterparts on other rocky planets and moons because they have been affected by the action of erosion by liquid water. In comparison to the Moon, Mars’ craters deviate much more from their original geometries, but perhaps more strikingly, more than 400 craters on Mars’ surface have an inlet valley (Image 1); a valley which starts from outside the crater and crosses the rim crest (e.g. Cabrol & Grin, 1999; Goudge et al., 2016). Although no substantial liquid water currently flows on Mars today, the preserved valleys likely delivered water from a crater’s surroundings to the crater interior, at some time in the distant past. Therefore, their formation could give clues to Mars’ watery past.

Image 1: An impact crater on Mars, at 16.2°N, 53.2°W with a high-standing crater rim around its circumference. To the south of the crater, there is an inlet valley that crosses the rim divide, with two wide tributaries. The valleys are now dry, but liquid water in Mars’ past likely incised them. The crater does not have an outlet valley (where water may have exited the crater in a through-flowing system). Background is a CTX DEM (from the stereo pair B21_017806_1955 – B21_017951_1955), HRSC DEM h2277_0000 and global MOLA DEM, overlain on CTX image B21_017806_1955 and THEMIS global IR mosaic.

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Evidence against vast glaciation in Mars’ grandest canyons

Post by Miss. L. Kissick, PhD candidate, Department of Earth Sciences, University of Oxford. Research conducted while at the Department of Geography, Durham University.

The Valles Marineris (Image 1) form the largest system of interconnected canyons on Mars, up to 2000 km long and in parts 10 km deep, and have long been a focal point of interest in planetary geomorphology. Recently, researchers including Mège and Bourgeois (2011), Cull et al. (2014), and Gourronc et al. (2014) outlined the case for a vast glaciation filling these canyons to several kilometres in depth. The implications of such a fill on the climate history and global water budget of Mars would be paradigm-shifting, but with high resolution imagery, features attributed as glacial may be better explained by more common geomorphological processes.

IM1

Image 1: Valles Marineris in Mars Orbital Laser Altimeter topography. This enormous canyon system is in parts 10 km deeper than the surrounding plateau, and was hypothesised to contain a glacier of a volume comparable to each Martian polar cap (Gourronc et al., 2014). Rough areas described in Image 2 are circled. Image adapted from Figure 1 of Kissick and Carbonneau (2019).

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