Shades and textures

A Piece of Mars: This 480×270 m (0.3×0.17 mi) scene shows the contact between two very different terrains. On the left is a bright surface with polygonal cracks (characteristic of periglacial terrain – this is at a high latitude). On the right is a dark rippled sand sheet that superposes the polygonally-cracked surface. The long meandering furrows might be the beginnings of polygonal cracking in the sand, which might expand if wind doesn’t erase them. (HiRISE PSP_006473_1125, NASA/JPL/Univ. of Arizona)