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Melty dunes

ESP_039610_1150_1.0xA Piece of Mars: With all due apologies to followers of the show Coupling, I have to call these things “melty dunes”. This link shows what a crisp dune should look like. The dunes in this 600×450 m (0.37×0.28 mi) scene, however, have rounded crests and sand that seems to have ponded around the bottom of the dunes. These are common at high southern latitudes on Mars. (HiRISE ESP_039610_1150, NASA/JPL/Univ. of Arizona)


ESP_013785_1300_1.0xA piece of Mars: Ripples form endless chevrons in this 600×450 m (0.37×0.30 mi) scene. It’s really the crest of a dune that connects all the vertices in the chevrons, making that straight line that runs nearly vertical through the center. Wind from the south (bottom) is deflected by this crest and other local topography just out of the scene. This pattern has been there for at least 3 Mars years. How long will it last? (HiRISE ESP_013785_1300, NASA/JPL/Univ. of Arizona)

The bright barchan

ESP_039568_1120_0.794xA piece of Mars: Most dunes on Mars are dark, like these and these. So why is this one bright? It’s adjacent to a more typical, dark dune. It’s possible that there are two populations of sand here that are different enough in size or density, and so they respond to different winds – thus producing remarkably different dunes in the same location. (HiRISE ESP_039568_1120, NASA/JPL/Univ. of Arizona)

Sometimes I just have no idea

ESP_039595_1230_0.631xA piece of Mars: The smooth areas are eroded dunes, separated by fields of boulders (the scene is 1.51×1.14 km or 0.93×0.71 mi). The largest boulder near the center is 7.5 m (25 ft) across, the size of a small RV. The interesting wave patterns on the lower sides of the smooth dunes… well, I don’t know. My best guess is it’s another type of bedform created from the sand of the smooth dunes. Do you know? (HiRISE ESP_039595_1230, NASA/JPL/Univ. of Arizona)

Dunes ignoring small hills

ESP_039524_1445_1.0xA piece of Mars: What happens to dunes as they move over rough terrain? This is what a barchan looks like on a relatively flat surface. If the hills are smaller than the dune, then it does its best to pretend they don’t exist, like the one in this image. It’s 175m (574ft) wide and 190m (623ft) long, with a slipface indicating overall migration to the northeast. (HiRISE ESP_039524_1445, NASA/JPL/Univ. of Arizona)

On Mars, the wind wins

ESP_039057_1485_1.0x A piece of Mars: This scene (600×450 m or 1969×1476 ft) is covered in small craters, formed by the splash of a larger crater nearby. They cover everything, even the bright ripples visible on the right. So the ripples were there before the impact that formed all these little craters. And yet… there are itsy little gray ripples on the upper right, merging with the crater rims – these are new ripples, younger than the craters. On Mars, it’s the wind that wins in the end. (HiRISE ESP_039057_1485, NASA/JPL/Univ. of Arizona)

Wind eroded mantle

ESP_039195_1755_0.398xA piece of Mars: The curving ridge of a mountain has signs of many small landslides. Mantled on top of these is an older set of landslides that has been partially eroded away. The rippled edge of this older deposit suggests that it is wind that has done the erosion. So the history here goes: mountains, then landslides, then wind erosion, then new smaller landslides. (HiRISE ESP_039195_1755 NASA/JPL/Univ. of Arizona)

Bearded craters and dunes

A piece of Mars: This 600×450 m (1969×1476 ft) scene has a complex sedimentary history. How are bearded craters and dunes formed? They weren’t always bearded. At some point, a deposit of bright material accumulated on this surface, and was then eroded so that all that remains of it is what is protected by topography (anything that pokes up like dunes or crater rims). Can you find the boulder that has tumbled downslope (it too has a beard!). (HiRISE ESP_038826_1700, NASA/JPL/Univ. of Arizona)

The long, low dune

ESP_038615_1665_1.0xA piece of Mars: A long, low dune covered in long, linear ripples stretches across the scene (600×450 m; 1969×1476 ft). Dark gray areas on the dune show where sand has most recently moved. A small slip face has formed on the southeast side of the dune, but ripples have formed on it, so there haven’t been any recent avalanches here. (ESP_038615_1665, NASA/JPL/Univ. of Arizona)

Wind, wind, impact(!), and then more wind…

ESP_038918_1650_0.437xA piece of Mars: Some time ago, something hit the ground on Mars and made this impact crater, right into a field of ripples. Stuff thrown up during the impact fell back down, burying the ripples with the gray ejecta rays that radiate from the crater. But the wind kept blowing, and in some places you can see where new ripples have formed on top of the ejecta. That’s Mars for you: wind, wind, wind, impact(!), more wind… (HiRISE ESP_038918_1650, NASA/JPL/Univ. of Arizona)