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HolidayBuyer's Guide

Carbon-dioxide snowfall

Seasonal changes on Mars

Patchy frosted dunes

Ribbony layers at the North Pole

Ink spots dotting Mars

As temperatures fall, frost begins to form

Summertime at the South Pole

Thawing Richardson Crater dunes

Frosty dune slopes

Frosted gullies

Fans of sand on ice

Winter gullies

Last year, data collected by NASA's Mars Reconnaissance Orbiter gave scientists a clearer picture of Mars' carbon-dioxide atmosphere and revealed the only known example of carbon-dioxide snow falling anywhere in our solar system.

"These are the first definitive detections of carbon-dioxide snow clouds," said the report's lead author, Paul Hayne of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We firmly establish the clouds are composed of carbon dioxide -- flakes of Martian air -- and they are thick enough to result in snowfall accumulation at the surface."

Temperatures of about minus 193 degrees Fahrenheit are required to freeze carbon dioxide, and as the atmosphere freezes it is deposited on the Martian surface in a way unlike anything we know on Earth.

Fall and winter temperatures bring seasonal changes to Mars as the carbon dioxide rich atmosphere turns to dry-ice frost, and sometimes snow, which clings to the surface. Take a look at some of the amazingly detailed wintry scenes the Mars Reconnaissance Orbiter has captured of nature's beauty in a land far, far away.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
From early spring, on the left, through the Martian winter, changes can be seen on the sand dunes of Mars. A layer of carbon-dioxide ice, better known to us as dry ice, about 2 feet thick, begins to crack, and exposes dark sand below, as seen in the second panel.

Rising gasses, which had been trapped below the ice layer, then bring sand and dust to the surface, where it is deposited in a fan-shaped formation downhill and downwind, exhibited in the third and fourth panels.

The final panel shows more of the exposed dark dunes as the overlying layer of seasonal ice evaporates back into the atmosphere.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
Warming springtime temperatures have vaporized the frosty layers along the crescent-shaped dunes at the Martian North Pole, dotting the landscape with bare patches of dark sand.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
Layers of dusty water-ice deposits form ribbonlike bands along the Martian North Pole, where the ice is several miles thick.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
The features that look like ink spots are one of the unique patterns created when the Martian winter transitions to spring, and Mars' carbon dioxide frost begins to vaporize and reveal the ground below.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
In late fall, when the temperatures are falling, carbon dioxide in the Martian atmosphere condenses into ice and settles on the Martian surface. With spring and summer warmth, the frost will vaporize again to rejoin Mars' atmosphere.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
It stays cold enough to maintain permanent year-round ice near Mars' South Pole, but as temperatures rise, the defrosting walls of flat-floored pits, seen in yellow, stand out in contrast to the permanent carbon dioxide ice. The smallest of the pits, at the center, are the size of sports stadiums on Earth.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
In fall and winter, frost coats the dunes inside 34 mile-diameter Richardson Crater in the south polar region of Mars. Dark streaks and spots are the exposed sand in areas that are beginning to thaw.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
Here, frost is seen beginning to accumulate on south-facing slopes of sand dunes in late fall in the Aonia Terra region of Mars' Southern Hemisphere.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
The long streaks that stripe the walls of this crater are gullies in the Martian winter, where frost has built up on the cold slopes that face the pole.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
Ice-covered dunes crack in warmer springtime temperatures and allow sand beneath to blow into fan-shaped deposits on top of the ice. When the ice cracks at the crest of a dune, the sand sometimes slides down, leaving dark traces in the dune walls.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
The long streaks at the lower left of this image are the typical of gullies that form in the fall and winter when carbon dioxide frost is settled on the surface. Repeat observations of areas with these gullies are allowing scientists to probe why gullies form and how they shape the Martian surface.
Caption by / Photo by NASA/JPL-Caltech/Univ. of Arizona
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