Cosmic Diary by Lori Fenton

A piece of Mars: Here in the bottom of a crater in Coprates Chasma is the intersection of two sets of ripples: dark, dust-free ripples at the bottom of the crater, and lighter ripples formed from debris that has come down the rim of the crater. (HiRISE ESP_030927_1675, NASA/JPL/University of Arizona)

A piece of Mars: The source of dune sand on Mars is normally something of a mystery. But here on the interior wall of a small crater it appears that small gullies have eroded sediment from the wall and carried it down toward the center of the crater (toward the upper right). The bluish and tan regions are the material the gullies have transported, and the bluish sediments have formed into small aeolian ripples. The mystery is solved for this one small region of Mars: is it the same story elsewhere? (HiRISE ESP_030915_1290, NASA/JPL/University of Arizona)

A piece of Mars: Swirly loops form on the martian surface as dust devils pass by, cleaning up dust on the surface and revealing the dark, rippled dune beneath. Every year the swirls get cleaned off and reform — such patterns are known to occur in only a few select places on Earth, but they are common on Mars. (HiRISE ESP_031199_2070, NASA/JPL/University of Arizona)

A piece of Mars. The dark circle (~170 m across) in the middle of the picture is the interior of what used to be a crater. It’s now almost completely eroded away, probably by the wind. Small dunes have formed on these former crater sediments — because the dunes seem to form mostly on this circular plateau, it’s likely that they’re made from sand derived from the former crater sediments (and thus these dunes have not traveled far). (HiRISE ESP_030622_2060, NASA/JPL/University of Arizona)

A piece of Mars: Everybody else loves this image because it shows an inverted channel — the remains of a stream that once flowed through this area. But I love it because the little dunes were also formed by a flow. The flow of the wind, that is. Here the wind is deflected by the former streambed, forming dunes that moved in the same direction (lower right to upper left). (HiRISE ESP_030609_1550, NASA/JPL/University of Arizona)

A piece of Mars: Is it modern art? Well maybe it looks like it from a distance. Up close, this is reality on Mars. These are dark dunes in the southern hemisphere, awaking from a long hibernation beneath bright winter frost (a touch of which can still be seen in white patches). The wind has begun to shape the dunes, leaving crayon streaks where dust devils have swept by. Maybe we’ll see those little ripples move this summer. (HiRISE ESP_030602_1080, NASA/JPL/University of Arizona)

A piece of Mars: There are vast plains on Mars that display criss-crossing streaks like this. These are ~5 m (~16 feet) across, give or take. Did an alien drive a dune buggy all over, leaving behind tracks? Nope. These are the distinctive trails made by the passage of dust devils, which act like huge vacuum cleaners that suck up dust from the ground. The patterns of the tracks change every year as new dust devils churn away at the surface. (HiRISE ESP_030916_1250, NASA/JPL/University of Arizona)

A piece of Mars: Dunes near the north and south poles get cold in the winter, just like they do on Earth. Except on Mars instead of H2O ice, it’s a mix of CO2 and H2O ice (mostly CO2). In the spring the white ice slowly disappears, revealing the dark dunes underneath. (HiRISE PSP_002033_1325, NASA/JPL/University of Arizona)

A piece of Mars: Nili Patera on Mars is an ancient volcano. Some of the old volcanic material has been blown into rather striking sand dunes. It is the first place where dunes were conclusively identified as actively moving. Here’s a closeup of one of them — the steep slip face on the downwind side indicates these dunes are moving to the lower left. This dune migrates about a meter every year. (HiRISE ESP_030210_1890, NASA/JPL/University of Arizona)

A piece of Mars: Here are some old dunes that look a little like vertebrae of fossils (if you think they look like dragon spines poking out of the ground then you’re playing too many video games). The white areas are stabilized and possibly lithified. The blue areas are where the dunes are being actively eroding, exposing old bedding (faint parallel stripes) within the dunes. (HiRISE ESP_030583_1610, NASA/JPL/University of Arizona)

A piece of Mars: Not all piles of windblown sand are able to form proper dunes, with a fully developed avalanche on the downwind side. Here, bluish sand tries to make its way through hilly terrain, which both traps the sand and makes it difficult for slip faces (avalanches) to form. Smaller, now stabilized dunes in the upper right were also trapped by the hills. (HiRISE ESP_030570_1440, NASA/JPL/University of Arizona)

A piece of Mars: As the wind blows sand over terrain, the grains deepen grooves in weak materials, enhancing the topography in the direction of the strongest wind. Here, over eons, sand marching from right to left has formed dunes (oriented perpendicular to the wind) and elongated grooves downwind of low hills. (HiRISE ESP_030582_1850, NASA/JPL/University of Arizona)

A piece of Mars: Some of the dunes on Mars are just plain weird. Here are some feather-shaped ones. I’m not sure anybody knows why they form these fractal shapes just yet. I don’t know of anything on Earth that looks like these. (HiRISE ESP_028024_1830 NASA/JPL/University of Arizona)

A piece of Mars: Dark sand has been blown into the scene from the upper right. It has piled up against older, brighter dunes that may now be inactive. The sand drifts on and on, piling up where the wind weakens and carving out rock where the wind is strong. And that is geology on Mars today. (HiRISE ESP_028024_1830 NASA/JPL/University of Arizona)