THE COSMIC DIARY NETWORK

Arnus Vallis, Mars
Published 1/22/2018 in Lori Fenton's Blog Author lfenton
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 eastern wall). You're looking at a small section of what could be the longest dune on Mars. You can read more about the geology of this valley in this paper. (HiRISE PSP_007187_1920, NASA/JPL/Univ. of Arizona) read more ❯

Varying wind directions
Published 1/18/2018 in Lori Fenton's Blog Author lfenton
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 largest of which is ~4m across, about the size of a subcompact car), you'll see that a third wind blowing from the upper right to lower left has left some bright streaks in the wake of the boulders. This third wind isn't persistent enough to shape the dunes, so it... read more ❯

Dunes with comet tails
Published 1/8/2018 in Lori Fenton's Blog Author lfenton
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 that as the upper sections can be pushed downwind, the lower sections remain locked in place behind. This can happen on Earth too, but here it's usually the water table stabilizing the lower portions of the dunes (and many of the thick continental sandstones, like the Navajo sandstone, were built... read more ❯

Fuzzy dunes
Published 1/2/2018 in Lori Fenton's Blog Author lfenton
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 ❯

Buried by ejecta
Published 12/26/2017 in Lori Fenton's Blog Author lfenton
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 bedforms because the ejecta is thick enough to have buried them. The crater itself is fairly "young" for a geologic feature on Mars, but enough time has passed to allow small bedforms to accumulate inside it (ripples like these don't form overnight). (HiRISE ESP_052794_1545, NASA/JPL/Univ. of Arizona) read more ❯