Giant cracks that crisscross to form polygons have been imaged on the floors of hundreds of Martian impact craters by NASA's Mars Reconnaissance Orbiter. Scientists have been aware of them for years, but assumed they resulted from the expansion and contraction of the craters' floors due to temperature fluctuations.



However, new calculations by Ramy El Maarry of the Max Planck Institute for Solar System Research in Germany and colleagues suggest that under Martian conditions, this process cannot make polygons larger than 65 metres across. The observed polygons can be larger than that, spanning up to 250 metres.



The researchers suggest the cracks formed instead when lakes on the crater floors dried up, much as mud puddles on Earth leave cracks behind when they dry out.



El Maarry presented the findings on Tuesday at the European Planetary Science Congress in Potsdam, Germany.



(Image: JPL/NASA)

Polygons due to drying and cracking are also found on Earth at a variety of size scales. Dried mud puddles leave behind polygons a few centimetres across like those seen here.



(Image: M Ramy El Maarry)

The polygons in Coyote Dry Lake in California's Mojave Desert (left panel), which span 50 to 80 metres across, are closer in size to the Martian crater polygons (right panel). Coyote Dry Lake dried up thousands of years ago.



(Image: Google/JPL/NASA)