Summer is 'sublime' in sunny south of Mars

Three views obtained by Mars Global Surveyor of the same portion the layered terrain near the martian south pole. The differences in orientation are caused by the fact that the probe did not pass directly over the exact same spot in each view. By February, all of the frost is gone, revealing the underlying layered terrain surface.

February 23, 2000
Web posted at: 3:16 p.m. EST (2016 GMT)

PASADENA, California (CNN) -- The summer has warmed up the south of Mars, melting away much of its icy polar cap. And a spacecraft orbiting the red planet recorded the dramatic seasonal change in a series of photos, released this week by NASA.

An annual winter chills the southern hemisphere, creating around the pole a frost composed in large part of frozen carbon dioxide, or dry ice.

But the southern half of Mars has warmed up slowly into spring and then summer over the last six months. The seasonal change releases the ice directly into the atmosphere, a process known as sublimation, according to NASA, which described the images on its Mars Global Surveyor Web site.

The Mars Global Surveyor is currently in a polar orbit, giving its onboard camera a good view as the frost sublimed.

The three images document changes from August to February in an area near the south pole. Each view spans 3 kilometers (1.9 miles). The wavy lines in the top part of the pictures are exposed layers of the south polar terrain, according to NASA.

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Dark spots appeared as the surface began defrosting in August. Winds occasionally moved the darker material across the surface, leading to dark streaks, NASA said. But all the frost and streaks disappeared by February.

Whether summer or winter, the surface temperature on Mars chills in comparison to Earth. The average surface temperature is -67 F (-55 C), and in the winter it can plummet to as low as -200 F (-130 C).

Like the south pole, the north pole has a cap. The two caps wax and wane in opposite seasons during the martian year, which lasts 687 Earth days.

NASA's Jet Propulsion Laboratory in Pasadena, California operates the Mars Global Surveyor.