Cosmic Diary by Lori Fenton
A piece of Mars: What is this big swoosh? It’s a big dark dune. The dark/light striping across it is found in all of the dunes in this area, but what is it? We’re probably seeing the inside of the dune: the wind may so strong here that it erodes the highest point of the dune, showing off the interior structure. (HiRISE ESP_034909_1744, NASA/JPL/Univ. of Arizona)
A piece of Mars: On the floor of a crater in the southern midlatitudes, there’s a field of ripples. But wait, there are big ones that are very sinuous and small ones that are not. Why? Both are ripples, but they’re different kinds of ripples. The smaller ones (~3 m, or ~10 ft) are probably made entirely of sand, while the larger ones (~15 m, or 50 ft) are older and they’re probably made of a mixture of different grain sizes. (ESP_034801_1300, NASA/JPL/Univ. of Arizona).
A piece of Mars: Last week I wrote an image caption for Curiosity, showing both the HiRISE perspective and Curiosity’s image of the ripple crossing Dingo Gap. Read more on the HiRISE image page.
A piece of Mars: Yep, this is really Mars. It’s a tiny bit (600×450 m) of the southwestern side of a large dune in the southern midlatitudes. The dark lines are furrows that are thought to be carved by blocks of CO2 ice that slide down in the spring. The tiny stripes are ~4m wavelength windblown ripples that are just starting to get covered in seasonal frost. Both the furrows and ripples are likely to be active today. (ESP_034234_1255, NASA/JPL/Univ. of Arizona)
A piece of Mars: Here are two craters, each of which is ~240 m across. On the right is an old, very eroded crater. It has old, eroded ripples on its floor. The crater on the left is younger, with a mostly intact rim and even ejecta surrounding it. The ripples inside this crater are also younger: more crisp, and less broken-up. (HiRISE ESP_034482_1570, NASA/JPL/Univ. of Arizona)
A piece of Mars: On Oct. 15, 2013, Curiosity drove past a crater that has small dunes or ripples on its floor. In a new HiRISE image, you can see Curiosity’s tracks from that day (its 424th sol on Mars). While there, the camera took a nice panorama, so I thought I’d show what this crater and ripple field look like both from the rover and from orbit. Note the dark dunes and Mt. Sharp in the background of Curiosity’s image. (HiRISE ESP_034572_1755 NASA/JPL/Univ. of Arizona, GigaPan)
A piece of Mars: On martian dunes it’s all about lines, lines, lines. The prominent wavy ones on the left are thought to be erosional scars left by sliding blocks of dry ice. The little fingerprint-like lines are ripples, like those found on any Earth dune. All those lines tell us that the dunes are formed as the wind, ice, and sand interact over time. (826×620 m, ESP_021838_1300, NASA/JPL/Univ. of Arizona)
A piece of Mars: Where the wind blows strong and there’s a lot of sand, the surface gets scoured. Some bits of the ground, called yardangs, are more resistant and stick around: they take on shapes elongated in the direction of the wind (in this case, a wind from the lower right). Groups of them are often called “fleets”, as they sometimes look like inverted boat hulls. (993×745 m, ESP_034129_1820, NASA/JPL/Univ. of Arizona)
A Piece of Mars: Bright hills appear to be bearded (or perhaps mustached?). What’s going on? Dark sand has blown over some yellow-crested hills and settled on the downwind side, where the hill blocks enough wind that it can no longer move sand, and it all collects there in rippled drifts. (scene is 386×290 m, ESP_034084_1655, NASA/JPL/Univ. of Arizona)
A piece of Mars: A single dune sits on the surface of Mars, not too far from the north pole. It’s early spring, but this far north the dune is still covered in white CO2 frost (as well as a thin yellow layer of airfall dust). But the sun has done some work already: the dark spots are areas where enough frost is gone from the warm sun’s rays, revealing the lovely black sand beneath. Before long the frost will be gone and the dark dune will be fully released from its wintery blanket. (ESP_033729_2565, NASA/JPL/Univ. of Arizona)
A piece of Mars: Normally I post color images, but this one is just too cool to skip. These ripples formed ages ago: long enough ago that the impact of several small bolides formed craters (seen on the left), disrupting this ripple field (the largest crater is ~85 m across). After the impact, small ripples formed inside the craters, but they never grew to the same size as the original ripples. (HiRISE ESP_033717_1990, NASA/JPL/Univ. of Arizona)
A Piece of Mars: Two-toned ripples have formed on a steep slope, created by winds rushing downhill (from top to bottom in this frame). The larger ones are big ripples, with peaks more than 30 meters apart. What makes them unusual, however, is stark contrast between the dark (bluish) upwind side and the light (pale tan) downwind side. How did that happen? It’s because sand blowing downhill preferentially scours the dark upwind side of the ripples, leaving the downwind side untouched. (PSP_002208_1755, NASA/JPL/University of Arizona)
A Piece of Mars: These rocks look like hooded figures from some dark fantasy story. European standing stones should be jealous, they don’t typically get a shroud of dark sand to add to their mystery and etch them into beguiling shapes (but then perhaps they don’t need it). Here, sand moving from the upper right to lower left slowly carves out these lovely shapes. (PSP_007535_1755, NASA/JPL/Univ. of Arizona)
A piece of Mars: Is it a comet? With Comet ISON in the news these days it’s hard to tell. No, this is a brand-new meteorite impact on the surface of Mars. The impactor hit the ground, blasted through a layer of bright dust blanketing the surface, and threw out some underlying dark material. The long dark streak to the lower right shows where wind blew some of the dark material exposed by the impact. (HiRISE ESP_033302_2030, NASA/JPL/Univ. of Arizona)