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Erosional remnants

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A Piece of Mars: The erosionally-streamlined bright areas are on high ground. They are remnants of a vast dusty mantle that once covered this whole area – the rest of it has been blown away. The surrounding regions (check out the whole image) are still covered by that mantle, but here you can see through to the underlying, dark surface made of dark, cratered lava flows. (HiRISE ESP_017914_1685, NASA/JPL/Univ. of Arizona)

Ancient ripples?

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A Piece of Mars: Potential signs of wind activity are everywhere on Mars. Take this 0.96×0.54 km (0.6×0.34 mi) scene, which is on bedrock dated to be several billion years old. There’s a fabric of ridges trending from the upper right to lower left. The smaller and smoother ones are clearly windblown bedforms. The larger, bright ones are shedding boulders, so if they’re old bedforms then they’ve been lithified. How old are they? Billions of years old? Or did they form sometime in the intervening years? (HiRISE ESP_046389_1695, NASA/JPL/Univ. of Arizona)

Fossil dunes

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A Piece of Mars: This 1.92×1.08 km (1.19x 0.67 mi) scene shows eroded ridges that are, in fact, lithified dunes. They are so old that you might not recognize them as dunes without more context. This doesn’t happen much on Earth, where inactive dunes are quickly eroded, buried, and/or destroyed by other geologic processes, so enjoy this uniquely martian wonder! (HiRISE ESP_046597_1670, NASA/JPL/Univ. of Arizona)

Dunes not in the global dune database

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A Piece of Mars: Ten years ago I participated in a global survey of martian dunes. But we missed a few dune fields, like these beauties. They’re small, low, and in rugged terrain, which made them difficult to spot in the lower resolution data set we used. I keep a list of dune fields we’ll have to add if we get a chance to update the database. This scene is 0.96.0.54 km (0.6×0.34 mi) wide. (HiRISE ESP_043582_1555, NASA/JPL/Univ. of Arizona)

When the martian surface is eroded, pretty things emerge

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A Piece of Mars: Just like at Earth’s Grand Canyon, erosion on Mars has created some really beautiful landscapes. This 480×270 m (0.3×0.17 mi) scene shows rugged terrain that was once buried in sediment. Does the texture here represent the landscape before it was buried, or was it created in the process of scouring off all that overlying sediment? Probably a mixture of both. And we get a pretty view because of it! (HiRISE ESP_046198_1750, NASA/JPL/Univ. of Arizona)

Where we have been

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A Piece of Mars: This 0.98×0.54 km (0.61×0.34 mi) scene shows ancient windblown bedforms (maybe dunes) that have been partially eroded by the wind. The wind has left behind ghostly stripes: these are remnants of where these things once were, back when they were still actively migrating. Some of the bedforms have been almost entirely erased, except for those remaining bits. Much smaller (2-3 m wavelength) ripples have since formed between some of them, probably made from material scavenged from the larger bedforms. (HiRISE ESP_037700_1710, NASA/JPL/Univ. of Arizona)

Landslides unlike any on Earth

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A Piece of Mars: Click on this 0.96×0.54 km (0.6×0.33 mi) scene to see it in detail. Many thin, narrow landslides have formed on these dust-coated hills. As far as I’m aware, there’s nothing like this on Earth. Inside the landslide scars, there are small dusty ripples about 1.75 m (~6 ft) in wavelength, smaller than the ripples found on dark sandy dunes. These landslides are visible in images at least as far back as 2007, although they clearly formed after the small crater on the slope (which is slowly being filled with the dusty debris). (HiRISE ESP_045605_1715, NASA/JPL/Univ. of Arizona)

How to hide geology on Mars

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A Piece of Mars: Three things are trying to hide in this 0.96×0.48 km (0.6×0.3 mi) scene. 1) Craters are slowly being both scoured and buried by migrating sand, 2) the sand itself is hiding in the lee of crater rims and other topographic obstructions to the wind, and 3) small patches of ice (blue in this stretch) are hiding on shady slopes (north is to the right in this southern hemisphere image, taken during southern winter). (HiRISE ESP_045792_1395 NASA/JPL/Univ. of Arizona)

New craters and wind

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A Piece of Mars: The two small dark craters (2.25-2.4 m, or 7.4-7.8 ft across) are brand new, having appeared in CTX images sometime between May 2007 and April 2008. They punched through a layer of bright dust and threw up some darker material, which the wind carried downwind (near-surface winds blowing from the southwest, and higher winds blowing from the southeast). Application of an atmospheric model could further constrain the season and time of day when the impact happened, based on the prevailing wind direction. This picture from May 2016 shows the wind streaks are still there, having faded only a little in the 8-9 years since they formed. (HiRISE ESP_045798_1965, NASA/JPL/Univ. of Arizona)

Itty bitty changes: places where the wind barely moves sand

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A Piece of Mars: Not all dunes on Mars are moving at a measurable pace. This 0.96×0.45 km (0.6×0.28 mi) scene looks a lot like one I posted 3 years ago called Martian Sports. This image shows the same dunes 9.5 years apart (that’s 5 Mars Years). There are a few places where patches of sand have appeared or been removed, but it would take some detailed work to figure out whether the bulk of the dunes has shifted much. In the first post I guessed that the upper dune would crash into its topographic hurdle in 20 years, but after nearly 10 years of relative inactivity, I’ll have to revise that estimate upwards to perhaps 100 years. (HiRISE <a href="http://www.uahirise.org/ESP_045785_1995"ESP_045785_1995 NASA/JPL/Univ. of Arizona)