Dunes with comet tails

A Piece of Mars: The north polar dunes in this 575×325 m (0.36×0.2 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

Dunes fighting for survival

A Piece of Mars: Having a bad day? You’re in good company with these dunes in this 0.96×0.48 km (0.6×0.3 mi) scene. The gray barchanoid dunes are covered in ripples, as the wind valiantly tries to push the sand to the dune crests. But they are besieged by other processes at work. Dark scribbles show

Crater ejecta on old ripples

A Piece of Mars: Mars rarely does anything without drama. Long ago in this 0.96×0.54 km (0.6×0.34 mi) scene, large ripples formed and then, presumably, lithified (turned into rock). Some time after that, an impact formed the crater in the center, throwing debris into an ejecta blanket that covered the lithified ripples. That ejecta blanket

Bedforms on crater rims

A Piece of Mars: Dunes and ripples most commonly form in topographic lows. But not in this 0.96×0.54 km (0.6×0.34 mi) scene. Here, and in other places on Mars, these bedforms (called TARs) form on plains, and sometimes appear to cling to the rims of craters – which are topographic highs, not lows. It’s not

Ancient ripples?

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,

Fossil dunes

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

Giant “combs” on Mars

A Piece of Mars: This 480×270 m (0.3×0.17 mi) scene shows a herd of 100-300 m fine-toothed combs grazing on the surface of Mars. Wait, what? No, it’s not really combs. This is actually a landscape covered by two sets of windblown bedforms. The larger ones (the “comb” shafts) are very old, now inactive windblown