Martian spring reveals frozen water at south pole

August 2, 1999 marks the spring equinox for the martian southern hemisphere  MESSAGE BOARD: Destination Mars

August 3, 1999
Web posted at: 10:04 a.m. EDT (1404 GMT)

(CNN) -- Monday marked the spring equinox for the martian southern hemisphere, which has crept into sunlight in the past month giving NASA's Mars orbiter a first-ever look at a melting winter wonderland of frozen water at Mars' south pole.

The latest images released by the Mars Global Surveyor mission show white ice retreating from the planet's southern polar cap.

"It's the first time we've seen the southern hemisphere," said Michael Malin of Malin Space Science Systems, which took the pictures for NASA. "It's been in winter for much of the last year. Mars is tilted on its axis like the Earth is. For half the year at the pole you don't get any sunlight."

For the past five months, about when Global Surveyor started mapping and photographing Mars, the planet's south pole has been shrouded in darkness, keeping the spacecraft's camera from snapping any useful shots of the ice cap. Conditions have changed as the planet has tilted on its axis.

"The sun is moving into the southern hemisphere and we're getting better illumination conditions," Malin said. "In the north we're moving to the fall and it's starting to get stormy and cloudy."

Theoretically, the snowy images show what could be frozen water or carbon dioxide. But Mars' surface temperatures now (about minus 184 F or minus 120 C) are above the freezing point of carbon dioxide, ruling out that solid and leaving the conclusion that the frost must be water-ice.

One of the newly released images, a wide-angle view of Mars taken in late July, shows rusty wisps of dust storms tracking north across the margin of Mars' south polar cap, with the southernmost of the large Tharsis volcanoes visible in the upper left of the photo. That volcano, Arsia Mons, is about 350 km (220 miles) across.

Another pair of photos taken July 18 show the extent of the frost-covered surface of Mars which stretches from 57 degrees South to the south pole. The snow-covered surface of Malea Planum, south of the giant Hellas impact basin, is featured.

Global Surveyor, which arrived at Mars in 1997, is the first mission in NASA's Mars exploration program managed by the Jet Propulsion Laboratory in Pasadena, California.