HiRISE images

A Piece of Mars: Get out your red and cyan glasses to see an old crater, which fills this 0.775x0.7 km (0.48x0.43 mi) scene. The crater punched through many thin layers when it formed, some of which you can still see in around the rim. The crater is filled with many small dunes called transverse aeolian ridges (TARs), given this laborious and generic name because they aren't quite like dunes we find on Earth and we don't yet understand what they are. The TARs are common in this area, but there are even more here, where sand is swept into... read more ❯

A Piece of Mars: Water carved this ~800 m (0.5 mi) wide channel billions of years ago. The water dried up, and since then it's been sand that flows through here (from the right), building up lovely dunes. A single crater on one of the dunes indicates that they're not very active (dunes of this type on Mars all seem to be inactive, unlike their bigger, darker cousins). Look closely between the dunes and you might see a few little dots - these are boulders that have fallen, weathered out from the channel walls. (HiRISE ESP_022693_1530, NASA/JPL/Univ. of Arizona) read more ❯

A Piece of Mars: Sometimes I just want to show the interior of a dune field, because it's full of waves: ripples and dune crests, slip faces, all of which signs of movement. The dunes in this 0.67x0.47 km (0.41x0.29 mi) view have been made by two winds: one blowing from the top of the frame, and a more-recently-active one blowing from the right. Together, these two winds (and gravity) push this sand between a series of hills and down into Coprates Chasma, one of the longest canyons on Mars. (HiRISE ESP_035278_1655, NASA/JPL/Univ. of Arizona) read more ❯

A Piece of Mars: Sand pours in from the top of this 1.95x1.95 km (1.21x1.21 mi) scene. The sand piles up and up (here ~115 m or 377 ft high), but ahead (at the bottom) is a mountain poking up. Like water diverting around a rock in a stream, the mountain affects the air flow just upwind of it, causing the sand to move around it. The steep dune slope is a slip face, caused by oversteepened sand avalanching. If you look closely, you'll see some of those narrow avalanches near the bottom of the slip face (those at the... read more ❯

A Piece of Mars: In a recent post (Dunes in a Colorful Hole), I showed some dunes crawling over layered terrain, with a view that looked a lot like some desert regions of Earth. Here's another spot on Mars (0.95x1.1 km, 0.59x0.68 mi) showing yet more beautiful layers with dunes filling up the valleys. Part of what makes it seem Earth-like is the lack of craters, although if you go looking you'll see there are some there. It's hard to tell from here, but this whole scene is inside an old fluvial channel. The layers are thought to be lake... read more ❯

A Piece of Mars: This 0.95x0.95 km (0.59x0.59 mi) scene shows an eroding surface punctured by some old craters. Long, thin lines seem to form in the wake of many brighter knobs. Are those thin lines windblown in origin? They look like erosional features - things that are left behind when other stuff erodes away around it (not like sand dunes, which are things that pile up over time). If so, they don't look like typical yardangs, which are streamlined bedrock, formed as sand wears down the rock. But this isn't typical bedrock - it is easily erodible material. The... read more ❯

A Piece of Mars: A fluid is something that fills a container it's put into, and it includes both gas and liquids. This 0.7x0.5 km (0.43x0.31 mi) scene shows hills of sediment left behind by two different fluids (wind and ice). The hill on the left is a rippled sand dune, which has been piled up by the wind as it drops its sandy load. On the right is a layered sinuous hill, leftover from when ice flowed down a slope offscreen to the right. The dune is slowly encroaching on the hill, and will eventually be disrupted by it.... read more ❯

A Piece of Mars: Gray dunes have migrated over reddish rock, moving toward a narrowing cleft surrounded by tall tan cliffs. Bright lines on the dunes are exposed internal layers (bones of the dunes, really) that show you where the lee-side slopes once were (so you can tell they've moved to the left). The cliffs are made of layered rocks (extra points if you can find the fault), suggesting these are sedimentary layers, laid down long ago in Mars' geologic past. The whole HiRISE image is worth a long look, it's really amazing. (HiRISE ESP_049009_1520, NASA/JPL/Univ. of Arizona) read more ❯

A Piece of Mars: This is the crest of one of the largest dunes on Mars (0.5x0.5 km or 0.31x0.31 mi). The wind mostly blows from the right, slowly pushing sand up the windward slope. But frost accumulates on (and probably in) the sand during winter, and sometimes it gets too heavy and slides down the steepest slope (toward the left), carving out big gullies in the sand. And then the wind blows some more, trying to erase the gullies by 1) making ripples, 2) burying the gullies (the featureless blue patches are grainfall, which is a fancy term for... read more ❯

A Piece of Mars: Is this 480x270 m (0.3x0.17 mi) scene showing a 150 m (492 ft) wide yin-yang symbol on Mars? Sort of, maybe, if you blur your eyes and lend me artistic license, but it's not doing so intentionally. One side of the crater is dark and the other is light. Both have their tone because of windblown material blown from the same direction, but the different materials collected where they did for different reasons. The dark material is probably mafic sand (iron and magnesium-rich, like what's found near many volcanoes), which was bounced along the ground from... read more ❯