<p>Polygons in Impact Craters: Polygons usually form from the expansion and contraction of subsurface ice.
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NASA/JPL/University of Arizona (5 km across, <a rel="nofollow" class="external text" href="http://www.uahirise.org/ESP_044251_2470">www.uahirise.org/ESP_044251_2470</a>)
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/71688597@N05">UAHiRISE (NASA)</a>
2016-05-13 10:11
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/uahirise-mars/26897722272/">ESP_044251_2470</a>