Crater floor polygons: desiccation patterns of ancient lakes on Mars?

[1] Global mapping of intermediate‐size (100–200 m) polygonal troughs occurring mainly in impact crater floors was carried out using high‐resolution images from spacecraft currently orbiting Mars. Earlier works have classified these polygonal networks as periglacial features on account of their apparent occurrence at higher latitudes and morphological similarities to thermal contraction polygons (TCPs). Crater floor polygons (CFPs) have diameters ranging from 15 to 350 m. They morphologically resemble terrestrial TCPs and desiccation cracks. Their size distribution, however, is significantly different from that of TCPs that are ubiquitous in the high latitudes. An analytical model based on fracture mechanics reveals that under current climatic conditions, the maximum fracture spacing attainable by thermal stresses alone is 75 m at the most. More reasonable values fall within 18 and 22 m, which is the range for TCPs on Mars. As a result, we propose desiccation to be a dominant mechanism for the formation of CFPs without ruling out thermal contraction as a possible contributor in some cases. This implies that lakes or water‐rich sediments occupied the craters in the past. Many such aqueous environments have no apparent external source of water, and thus, hydrothermal processes occurring shortly after the impact event may be viable explanations for the observed evidence. The association of features, which correspond to terrestrial lakes such as sedimentary deposits, mounds, and shorelines, corroborates lake formation and their eventual desiccation to form CFPs. The variation of CFP sizes with location can be indicative of different hydrologic environments