Enigmatic clastic polygons on Mars

image-1Planetary Geomorphology Image of the Month, February 1, 2018: Laura Brooker (Open University, Milton Keynes, UK). Polygonal ground of centimetre- to decametre-scale is one of the most common features found in cold-climate regions on Earth and on Mars.

Polygonal shapes on Earth can form through a number of different processes including the thermal contraction of ice-cemented soils, forming fracture patterns known as thermal contraction polygons, through the freezing and thawing of ground ice moving clasts, in the case of sorted patterned ground, or through the dehydration of volatile-rich material, termed desiccation polygons.

Around a large crater found in the northern latitudes of Mars, named Lyot, we observe stunning and unusually large clastic polygons (Image 1), but how do they form? To understand landforms on Mars we turn to analogues on Earth and compare morphological data to look for similarities and differences.

The clastic polygons around Lyot crater are far larger than sorted patterned ground on Earth, and possible examples of patterned ground on Mars, which are typically only up to metres in diameter (Image 2). Such polygons require cold climates and a pre-existing layer of clastic material (Goldthwait, 1976; Wilson and Sellier, 1995). They transition from circular shapes and polygons to ellipses and then to stripes with increasing slope gradient (Washburn, 1956; Goldthwait, 1976)…. [More at link]

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