<p>Dark dunes make waves across the floor of Proctor Crater, a 93-mile-wide (150-kilometer-wide) basin on Mars, as seen in a picture by the HiRSE camera aboard <a id="sxan" title="NASA's Mars Reconnaissance Orbiter" href="http://hirise.lpl.arizona.edu/">NASA's Mars Reconnaissance Orbiter</a> released April 28.<br><br> The dunes are most likely made of fine, basaltic—or volcanic—sand that collected in the bottom of the crater, according to NASA. Patches of frost seem to light up the tops of some dunes, while large boulders dot the smaller ripples along the dune beds.</p>

Dark Dunes on Mars

Dark dunes make waves across the floor of Proctor Crater, a 93-mile-wide (150-kilometer-wide) basin on Mars, as seen in a picture by the HiRSE camera aboard NASA's Mars Reconnaissance Orbiter released April 28.

The dunes are most likely made of fine, basaltic—or volcanic—sand that collected in the bottom of the crater, according to NASA. Patches of frost seem to light up the tops of some dunes, while large boulders dot the smaller ripples along the dune beds.

Image courtesy NASA/JPL/University of Arizona

Space Photos This Week: Black Holes, Sahara Storm, More

Midsize black holes, a dust "wall" pushing across Africa, and recently made streaks on Mars feature among the week's best space pictures.

DON'T MISS THE REST OF THIS STORY!
Create a free account to continue and get unlimited access to hundreds of Nat Geo articles, plus newsletters.

Create your free account to continue reading

No credit card required. Unlimited access to free content.
Or get a Premium Subscription to access the best of Nat Geo - just $19
SUBSCRIBE

Read This Next

'World’s worst shipwreck' was bloodier than we thought
World’s first ultrasounds of wild manta rays reveal a troubling truth
Titanic was found during secret Cold War Navy mission

Go Further

Subscriber Exclusive Content

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet

Why are people so dang obsessed with Mars?

How viruses shape our world

The era of greyhound racing in the U.S. is coming to an end

See how people have imagined life on Mars through history

See how NASA’s new Mars rover will explore the red planet