Leeward and poleward

A Piece of Mars: The sharp line in this 0.625×0.625 km (0.39×0.39 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

Wind and maybe water too

A Piece of Mars: Along the right side of this 0.5×0.5 km (0.31×0.31 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

Light and dark

A Piece of Mars: This 0.96×0.54 km (0.6×0.34 mi) late winter scene is a study in contrast. The dark top half is uniformly rippled. This is the shady surface of the main windward side of one of Mars’ biggest dunes, in Kaiser crater. On the bottom is the sunlit side of the dune, strewn with

Wind eroded mantle

A piece of Mars: The curving ridge of a mountain has signs of many small landslides. Mantled on top of these is an older set of landslides that has been partially eroded away. The rippled edge of this older deposit suggests that it is wind that has done the erosion. So the history here goes:

Textured gullies

A piece of Mars. These are gullies on a martian hillside (upslope is to the upper right). Water may be what forms the channels, carrying soil and rocks downslope. The textured pattern of the lower slope is caused by the wind forming ripples on loose sediment that has been transported partway down the hill. (HiRISE

Dunes being buried

A piece of Mars: Most dunes on Mars are the freshest, youngest features around. Not so here. The bright dunes near the bottom here are slowly being buried by debris coming down from the gullies on the slope, coming from the upper left. (HiRISE ESP_029483_1470, NASA/JPL/University of Arizona).