This is a crop from a much larger image posted at Red Orbit yesterday showing what is tentatively interpreted as a salt flat on a playa. The polygonally jointed white material may be chloride salts such as halite and sylvite. If so, this would indicate the past presence of standing water, which, as the accompanying blurb states, would indicate "a habitable (but not necessarily inhabited) environment." It is being considered as a landing site for future rover missions. The RO post is here, and here's the full size image (2048 X 1536 px.), which is well worth a close look.