HiRISE images

A Piece of Mars: This 0.93x1.25 km (0.57x0.78 mi) scene shows what I'm starting to think are windblown features. I posted something similar to this once before, from a location not that far from here. In this one region of Mars there are parallel lines cut into the tops of hills. A geologist would first presume they were exposed, tilted layers. But the regularity of their spacing (especially when you zoom in) is a bit unusual, and suggests some sort of self-organization (like windblown ripples). And then the questions begin: why just in this spot on Mars? what's unusual about... read more ❯

A Piece of Mars: There's a fabric of erosion in this 1x1 km (0.62x0.62 mi) scene, with the main wind blowing from lower right to upper left (and if you look carefully you'll see there's a second, subtler fabric a bit clockwise from that one). The result is a landscape strewn with streamlined rock called yardangs. The darkest areas are shadows from rock faces scoured by the wind so deeply that they've been undermined until there's overhang. Normally this would lead to collapse features, like rock piles, but you don't see those here. That's an indication that the rock here... read more ❯

A Piece of Mars: In the floor of what might have been an old fluvial channel there are a bunch of really neat dunes (or maybe ripples, they're TARs and we don't know yet what they are). One spire pokes up here, ~200 m (656 ft) across and ~90 m (295 ft) tall. The TARs reveal the wind direction here, as wind flowed from top to bottom around the spire, converging on the lee side. (HiRISE ESP_026557_1525, NASA/JPL/Univ. of Arizona) read more ❯

A Piece of Mars: Dunes in the top row in this 0.73x0.47 km (0.46x0.29 mi) scene are dark but those in the lower row are brighter. Why? They're all probably made out of the same kind of sand, which is dark. And they all probably got covered by fine-grained airfall dust, which is bright. At some point after that, a wind blew, probably from top to bottom of the view, and moved enough sand to kick off the fine bright dust. But the relief from those top dunes took energy from the wind, so that by the time it reached... read more ❯

A Piece of Mars: The wind on Mars likes to make textiles (unfortunately the term geotextiles is already taken for other purposes). This 1x0.6 km (0.62x0.37 mi) scene shows two different sets of ripples. The larger set has straight to wavy crests, and they're ~18 m (~59 ft) apart, which is pretty big for ripples (really they're TARs). Inbetween those (click on the picture so you can see them) are small ~2 m (~6.5 ft) ripples that make Mars look like it's made of kahki corduroy (which is a thing but it's not on trend, so Mars could stand to... read more ❯

A Piece of Mars: It's all about wind scour here in this 0.75x0.75 km (0.47x0.47 mi) view. The big "swoop" is an erosional channel dug into the surface by winds (blowing from the lower left) trying to erode the hills in the center. But notice that the hills are all aligned to the upper left/lower right, like a school of fish swimming the same way). That alignment tells us there's a second wind that came along later, blowing (I think) from the lower right. That wind also left behind some ripples (TARs, really) that swirled around the older big... read more ❯

A Piece of Mars: This 0.95x1 km (.59x.62 mi) scene shows the center of a small dune field. The dunes are shaped by three winds blowing from three different directions: from the west-southwest, east, and south. The north-facing slopes are slip faces made by the south wind, and most of them have bright patches on them that are probably accumulations of airfall dust. Whatever winds brought the dust, none have yet been able to remove it. I'd bet that one of the most recent winds to pick up sand on these dunes blew from the south, because those bright dust... read more ❯

A Piece of Mars: The sharp line in this 0.625x0.625 km (0.39x0.39 mi) scene is the crest of a long dune in Mars' southern hemisphere. The sunlit side is also the lee side: the bright streaks are thin sand avalanches (grainflows) that formed when the wind blew too much sand over the crest from the other side. The dark side is completely different. It's the side facing toward the south pole, and it's covered in ripples and erosional gullies that are thought to form when winter ice blocks roll down the darker slopes. (HiRISE ESP_024304_1345, NASA/JPL/Univ. of Arizona). read more ❯

A Piece of Mars: This 2.88x1.13 km (1.79x0.70 mi) scene shows quintessential Mars, with a 670 m diameter impact crater heavily modified by wind erosion. Both the crater floor and the surrounding terrain are covered by what is likely loosely-cemented dust. The texture is that of wind-eroded materials, but to make this texture that material must be fine-grained and uniform in cementation (except where punctuated by craters that are, in turn, also wind-eroded). I've never seen a texture like that on Earth. Check out the whole HiRISE image to see how extensive that texture is (and note that I've only... read more ❯

A Piece of Mars: Along the right side of this 0.5x0.5 km (0.31x0.31 mi) scene is the rim of a crater - the stripes are layers exposed (and then perhaps draped by falling ejecta) as the crater formed. To the left is the crater's interior wall, dropping downward. Deep gullies have been eroded into the crater walls, probably by water, carrying sediment downslope. Rivers and landslides are generally great sources of sand-sized sediment, and this place is no exception. The sediment piled up downslope, and then the wind came along and sculpted it into beautiful cross-hatched patterns (click on the... read more ❯