<p>Pits and Cracks in Crater in Protonilus Mensae — Pits may be the precursors to cracks, and cracks may enlarge to form troughs and ridges. It has been suggested that pits are caused by material collapsing into voids. Ice sublimating from the ground could produce voids.
</p><p>NASA/JPL/University of Arizona (300 km above the surface and north is to the right). 
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<a rel="nofollow" class="external text" href="https://www.flickr.com/people/71688597@N05">UAHiRISE (NASA)</a>
2018-03-06 09:49
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