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Tuesday, 11 April, 2000, 10:15 GMT 11:15 UK
Martian mysteries at poles
Mars south pole
An eroded trough displays the edges of the layers
By BBC News Online science editor Dr David Whitehouse

The poles of Mars, among the most exotic planetary landscapes anywhere in our Solar System, have been revealed in unprecedented detail by the images taken by the Mars Global Surveyor (MGS).

Pictures released on Monday unveil features of the unique layered terrain at Mars' south pole. These may well hold the secret of the planet's climate history for the past 100 million years but scientists remain baffled as to how the features formed.


Mars polar crater
The cause of these polar craters is not known

MGS flew over the region in October 1999, which was during the local spring season.

Layers of history

On Earth, geologists study layers of rock to determine the history of our planet. Rocks initially formed as layers of sediment laid down in an ancient sea can be deciphered by knowing that older layers are found beneath the younger layers.

Scientists investigating changes in Earth's climate over the past few million years also use this principle to examine cores of ice from Greenland and Antarctica. Layered rock and layered polar deposits on Mars may also preserve a comparable record of that planet's geologic and environmental history.

Some of the fine layers on Mars may have formed by the slow accumulation of dust and ice, perhaps only 100 micrometers (0.004 inches) per year. A layer 10 metres (33 feet) thick would therefore take 100,000 years to accumulate. This is roughly equal to the timescale of climate changes predicted by computer models.

Taking a closer look at the layered terrain was one of the chief goals of the ill-fated Mars Polar Lander that crashed onto the south polar region last December

Erosion puzzle

Planetary geologists think that the materials that comprise the south polar layers include frozen carbon dioxide, water ice and fine dust.

One of the images shows complex landforms caused by erosion. The exact method of erosion is not known but may be a combination of wind, ground-collapse and sublimation, when ice turns directly to gas without melting.

"We have a concept that these things are recording changes in the Martian environment, but we don't know exactly what process is doing it," said Michael Malin, of Malin Space Science Systems which operates the camera on MGS.

The smallest details that can be seen in the images are about 25 m (82 ft) in size.

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See also:

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