Polygons are of great interest because they often indicate the presence of shallow ice or of desiccation such as in a mud flat. However, nature sometimes seems too clever for us.

Polygons form by the intersecting ridges of sand dunes . If this deposit were to become indurated and eroded, we might not be able to tell that they originated as wind-blown dunes, and interpret the polygons as evidence for a dried-up lake, for example. Dunes often accumulate in the bottoms on craters, also a good setting for a (temporary) lake.

The illumination is coming from the upper left, so the bluish ridges are high-standing.

Written by: Alfred McEwen (audio by Tre Gibbs)   (15 May 2013)

More info and image formats at http://hirise.lpl.arizona.edu/ESP_031138_1380

Image: NASA/JPL/University of Arizona