Imagine you're floating high above Mars, soaring across the butterscotch-tinted landscape. Up ahead, you spot something odd, a series of lines and weird shapes, just downwind from a dotting of high mesas. What do you think that would look like? I bet it would appear to be something like this:
[Click to see it embiggened, or click here to see it really cromulently embiggened] That picture is from just about my favorite camera in the whole solar system: HiRISE, on the Mars Reconnaissance Orbiter. With a resolution of a half-meter per pixel it has been taking breathtaking images of the Red Planet. This particular picture shows a region in the southern mid-latitudes of Mars, just west of the Hellas Basin, a vast impact depression 2700 km across. On the left are two large mesas, flat-topped hills. As the wind whips around them, it blows sand into those long, linear dunes called seifs. The seifs themselves can break up and form the horseshoe-shaped dunes called barchans. I imagine that given time, and a hefty budget, this is what Salvador Dali's beachhouse property would look like. Here's a closeup of the right center of the image:
The lighter object is another mesa, though the top is not quite flat. You can tell from the shape of the hill the wind is blowing from left to right and has been for a long, long time. The barchans look smooth, but they don't need to be; the wind can carve ripples into them as well:
[Again, click to enlarge and see the gorgeous detail.] Think of them as dunes on dunes. Funny. On TV shows and in movies, there's a tendency to make planets all one environment (the ice planet Hoth, or Vulcan and Arrakis as desert worlds). But when we look at the planets in just our own solar system -- all born from the same parent disk of gas and dust 4.6 billion years ago -- we see diversity on a magnificent scale. Features rare on Earth (like seifs) are common on Mars, and Mars itself, though apparently fairly dead and lacking any extant water, has an incredible landscape of astonishing beauty and complexity. What will it look like when we go there, stand on the crest of a seif, and look out over to the Martian horizon? What wonders will those humans be able to see? Image: NASA/JPL/University of Arizona
