Sand dunes (left) probably eroding from ice sheets (right) near Mars' North Pole
(Malin Space Science Systems, MOC, MGS, JPL, NASA, apod020604)
Detail of frost-covered layers of dust, ice, and sand in an eroded scarp near Martian North polar cap
(location 85.2N, 4.4W)
Water ice in the permanent portion of the Martian Northern polar cap
(MSSS, JPL, NASA, apod020219)
Pinkish-white Martian polar dunes, colored by dry ice on reddish sand, begin to thaw.
(HiRISE, MRO, LPL (U. Arizona), NASA, apod080303)
A pinkish-white landscape of dry ice covered Martian polar dunes thaws, revealing dark sand.
Sand cascading downward creates streaks resembling trees which cast no shadows.
(HiRISE, MRO, LPL (U. Arizona), NASA, apod100119)
Above and below, thawing Martian polar ice creates avalanches, raising dust and ice clouds.
(HiRISE, MRO, LPL (U. Arizona), NASA, apod080311)
The permanent Martian South polar ice cap at its smallest extent
The South polar cap during the Martian Spring of 2001
(Malin Space Science Systems, MOC, MGS, JPL, NASA, apod011213)
 Strange ice structures near Mars' South Pole, presumably caused by evaporation and condensation of dry ice. The flat-topped mesas stand about 10 feet above the surrounding indentations. (Malin Space Science Systems, MGS, JPL, NASA, apod010327)
 A 20-mile wide Martian crater contains water ice protected from the Sun's rays by its high latitude (70 degrees North), which keeps the Sun so low in the sky that it isn't above the crater walls for very long even when at its highest. (G. Neukum (FU Berlin) et al., Mars Express, DLR, ESA, Nature, apod050720)
 Black dots lie scattered across ice-covered sand dunes near the Martian North Pole. At the time this image (Malin Space Science Systems, MOC, MGS, JPL, NASA, apod040831) was taken in July 2004 it was presumed that as the polar Spring began, carbon dioxide subliming (evaporating directly) from dry ice to gas produced these irregular patterns by uncovering darker underlying material. Further images (below) indicate that the dark spots are typically fan-shaped, suggesting that the dark areas may be caused (bottom image) by carbon dioxide geysers in which the material below the dry ice heats, vaporizes and blows a hole in the surface ice, scattering dark material across the surface.  Above, dotted dunes and fans near the Martian South Pole. Below, spidery networks near the Martian South Pole. (both images, THEMIS, NASA, JPL, MSSS)
Below, an artist's conception of sand and dry ice geysers at the Martian South Pole.
(Ron Miller, ASU, THEMIS)
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