A piece of Mars: Dunes near the north pole of Mars form in a very cold environment. Winter ice continually tries to stop them in their tracks, which makes for unusually rounded dunes like these. (HiRISE ESP_027451_2635) read more ❯

A piece of Mars: What an intriguing mess this is. These are dunes or ripples, oriented every which way, and mottled with white spots. The different orientations tell us that the winds blow from several different directions, on timescales long enough to seriously influence the dunes. The mottling is a mystery. (HiRISE ESP_025386_1800) read more ❯

A piece of Mars: You can't easily tell here, but you're looking at a steep slope that is high at the bottom of the image and flattens out at the top of the image (the small dunes at the top sit at the foot of the wall). What's neat here are the many small boulder tracks, formed as rocks get knocked down. A road through this canyon would need a sign saying "Warning Falling Rocks". (HiRISE ESP_026356_1960) read more ❯

A piece of Mars: I know, I keep showing ripples. But they're all so different. This one has a distinct swirl appearance, like it's stretched and twisted taffy. The complexities of the winds that create these things are not at all understood. (HiRISE PSP_003101_1320) read more ❯

A piece of Mars: Back in 2007, the Mars Exploration Rover Opportunity spent a great deal of time investigating the rim of Victoria crater. Here is the northern rim of the crater, showing three dark (bluish) sandy streaks formed by the wind as it blows dark sand out of the crater. You can see small dark ripples inside the crater, the source of the dark sand. And if you look very carefully you can see the tracks the rover left behind. (HiRISE PSP_009141_1780) read more ❯

A piece of Mars: My brain keeps seeing it as stuffed pillows, but it's the other way around -- the sun is coming from the upper left, so the centers of the little polygons are low and their edges are sharp-crested dunes. Or maybe ripples, we're still not sure. Stare at it until your brain makes it work that way. The little ripples inside them were formed after the big ones. I can tell because their orientation is so strongly affected by the topography of the big ones. (HiRISE ESP_026599_1500) read more ❯

A piece of Mars: Small, dark ripples have overridden larger, bright ones. The larger ones have some interesting shapes -- arcs, splits that resemble tuning forks, and even circles. Their shape is accentuated by the smaller, very regular ripples between them. (HiRISE PSP_004077_1325). read more ❯

A piece of Mars: Is it the latest in patterns for ties, or is it Mars? (Can it be both?) These are some unusually regular dunes on Mars, separated by a bouldered surface. The dunes have interesting pale bands common in this region on Mars, as well as an unending supply of long, parallel ripples. (HiRISE ESP_025108_1370) read more ❯

A piece of Mars: Many small craters on Mars are filled, at least in part, by small dunes or ripples. It's one of the distinguishing features of Mars -- a surface marked by geology both old (craters) and young (dunes). This particular crater isn't so old -- boulders surrounding it were made from rocks flung from the impact when it formed, and they are usually one of the first things to erode away as a crater ages. (HiRISE ESP_026726_1790) read more ❯

A piece of Mars: In the dustier regions of Mars, there are many small dark streaks on steep slopes that we don't understand well. Because we don't know much about them we call them "slope streaks", which is not the most imaginative name. They are actively forming on Mars today, though, and seem to be triggered by a disturbance like a nearby earth(mars)quake or a strong wind. Over the next several decades they slowly fade away. (HiRISE ESP_014394_2045) read more ❯