NASA craft discovers tree-shaped frost on Mars

NASA craft discovers tree-shaped frost on Mars

By DAVID HO

WASHINGTON (August 10, 1999 11:28 p.m. EDT http://www.nandotimes.com) - Peering down through stormy Martian skies, a NASA spacecraft has found tree-like shapes dotting the red planet's south pole. But what appears to be rolling hills covered with vegetation may be sand dunes topped with melting frost, scientists said Tuesday.

The latest images from the $250 million Mars Global Surveyor that has been mapping the planet since March offer new insight into the weather there.

"Since this whole area is at about minus 150 degrees Celsius, these are clearly not plants growing up out of the frost, but something else is happening," said Mike Malin, who is responsible for the camera aboard the spacecraft.

At first, the scientists thought the tree shapes and other, circular formations might have been caused by small gas pockets exploding under sand dunes.

But their latest theory is that the dark shapes are patches of exposed sand standing out among the frost-covered dunes. As spring warms southern Mars, the frost turns directly to gas. Wind then blows the frost and sand into patterns that resemble trees when viewed from space.

Unlike the monstrous sand dunes observed by the missions to Mars in the 1970s, the new images show smaller dunes, much like those found in the Mojave Desert. Detailed close-ups of the dunes look like a Japanese stone garden, with precise, wind-blown patterns etched into the dust.

"Our view of the red planet has been of something stuck in the freezer for millions of years, but looking at the new pictures shows us a dynamic and active planet," said Michael Meyer of NASA's Office of Space Science.

Most of the Martian frost consists of frozen carbon dioxide. But when the temperature rises, the carbon dioxide flashes into a gas too quickly to be observed, Malin said.

The frost appears at night, when Surveyor can't watch, so whether it forms on the ground or falls as snow from the atmosphere is still a mystery.

Two other NASA spacecraft will arrive at Mars later this year. The Mars Climate Orbiter will reach Mars in September and will make more detailed weather observations. In December, the Mars Polar Lander will arrive and dispatch two smaller probes to search for water below the surface. The Polar Lander will then touch down at the south pole to study the soil. NASA plans to announce the landing site on Aug. 25.