HiRISE images

A Piece of Mars: The dark splash pattern in this 0.9x0.9 km (0.56x0.56 mi) scene (click on it for a better view) is the site of an impact crater that appeared between images sometime between August 2006 and March 2010 (Smash!). The main crater is ~7 m (23 ft) across. Impacts smash a little ways into the ground, digging a hole and throwing out stuff that was once buried. Here, the buried stuff is darker than what's right at the surface. There are a lot of other similarly sized craters here, but they no longer have dark ejecta surrounding them.... read more ❯

A Piece of Mars: This is a section of Arnus Vallis (scene is 1.25x1 km, 0.78x0.62 mi). It's a >300 km long valley that was carved out, not by water, but by lava, long ago. Since then the wind has taken over. The left wall of the valley seems to have layers etched into high relief by wind scour; the floor is covered by ripples (TARs, really). But what I love most about this valley is that along the right (east) side, a long dune extends for much of the valley's length (it's why you don't see layers on the... read more ❯

A Piece of Mars: This 0.5x0.4 km (0.31x0.25 mi) scene shows two dunes near the north pole. The shape of the dunes indicates two main winds: one blowing left to right (which makes slip faces on the right side, one of which still has some bright white ice on it), and a secondary wind blowing from the lower right to upper left (elongating the upper "corners" of these dunes). The two lee sides are marked by yellow patches, where bright dust falls out of the atmosphere, accumulating in areas of relative calm. But if you look at the boulders (the... read more ❯

A Piece of Mars: The north polar dunes in this 575x325 m (0.36x0.2 mi) scene are made of dark sand covered by bright winter frost (which will soon sublimate away, as this image was taken in late spring). To the right of the dunes extend pale yellow bumpy hills, making the dunes look like they have little "comet tails". What's going on here? These dunes are migrating towards the left, so the tails are what they leave behind. The dunes are located very far north, where the ground is always frozen. Ice freezes the lowest parts of the dunes, so... read more ❯

A Piece of Mars: The dunes (or maybe they're ripples) in this valley appear to be fuzzy (the view is 625x775 m, 0.39x0.48 mi). They're not really fuzzy, but it's not actually clear what's going on. They seem to have smaller ripples superposed on them, and maybe bright dust has settled into the troughs between ripple peaks, so that they take on a striped, feathered look. It's unlike anything I've seen on Earth. (HiRISE ESP_052776_1785, NASA/JPL/Univ. of Arizona) read more ❯

A Piece of Mars: To see this one well you'll have to click on the image. At the lower right, a 240 m (787 ft) diameter crater formed when a bolide hit the surface, throwing out ejecta on the surrounding terrain. Zooming in, you can see that the ejecta has a distinctive rough surface. Farther from the crater there are smooth patches where ejecta didn't fall. What I like about this is the many small bedforms (ripples), some of which are covered by ejecta and some of which aren't. Closer to the crater, you don't see so many of these... read more ❯

A Piece of Mars: Some things just go unexplained (so far, anyway). Here's a mysterious bright streak (scene is 1.2x1.8 km, 0.75x1.12 mi) concentrated between two sets of ripple-like bedforms. It looks sort of like a river, but it's on flat terrain and it's not water. It's part of a larger set of bright streaks that you can see throughout the top of this broader CTX image (the bright streak shown in detail here is visible as a distinct white stripe on the floor of a crater). My guess is that at some point, probably at least several million years... read more ❯

A Piece of Mars: Look at the alignment of the ~100 m dunes in this 713x750 m (0.44x0.47 mi) scene. How do dunes form in such straight lines? And why don't they always do that? It's likely that these dunes were once long ridges stretching from the lower right to upper left. The shape of the slip faces suggests they're formed from two winds that blow from similar directions, both of which push sand toward the upper left. To stay stable, this sort of dune needs a constant influx of sand from upwind (from the lower right), but if that... read more ❯

A Piece of Mars: To the upper right of this 0.85x0.6 km (0.53x0.37 mi) scene is a flat-lying plain strewn with large ripples. To the lower left is a rugged hill with gray rock laced with white veins (this might be part of an impact megabreccia identified nearby in Holden crater). Notice that some of the ripples on the rugged hill are also veined - this is evidence that they are actually eroded into the bedrock, rather than fine-grained deposits like their counterparts on the plain. It's not yet clear how these "Periodic Bedrock Ridges" form, and they may be... read more ❯

A Piece of Mars: The rippled darker patch in this 600x600 m (0.37x0.37 mi) scene is the former site of a sand dune. This is one of a few "dune corpses" found just upwind of a dune field in Holden crater. The dunes are migrating to the south and east - you can see that the arc of this former dune opens to the south, the way a barchan slip face would. This dune is what's left behind after most of its sand has migrated downwind. (HiRISE ESP_052367_1540, NASA/JPL/Univ. of Arizona) read more ❯