By SHARON L. LYNCH Associated Press Writer
BOSTON (AP) -- Profiles of Mars' landscape etched with striking canyons and spiraling troughs have revealed what scientists believe may be the first evidence of ice outside the planet's polar ice caps.
Pictures released Wednesday at the American Geophysical Union's meeting show a crater some 30 miles across with a darker area 12 to 18 miles wide at the bottom.
The discoloration indicates a deposit of some sort -- maybe frozen mud or sand, which could indicate ice is present or water once was, said Mike Malin, a consultant who helped design cameras for the Mars Global Surveyor.
"If you're going to find life anywhere, that's where you're going to find it. Water is essential for life," Malin said.
But he and other scientists also cautioned that there may be other explanations for what they think they see in the crater, such as volcanic activity.
Cracks at the crater's rim, about 2,400 miles south of Mars' equator, are consistent with something seeping into the giant pit from its edge, Malin said. That could have been water, ice or lava.
The latest photos are from the Surveyor, a spacecraft orbiting the planet 108 miles above its surface.
The images have 10 to 12 times better resolution than any previously taken of the crater scientists are interested in, in part because the Surveyor is closer to Mars than any orbiting spacecraft has been before.
Surveyor has orbited Mars since last fall, collecting data on 59 separate passes. An altimeter on board is measuring 12,000-foot bulges in the polar ice cap and channels carved 3,600 feet into its surface.
Also Wednesday, Arizona State University researchers using Surveyor data said a concentration of a rust-colored mineral along the Mars equator indicates it once had boiling hydrothermal vents and perhaps huge lakes.
Geologist Philip Christensen said the hematite, an iron oxide, is the first clear evidence of widespread thermal activity on Mars.
"The existence and location of these deposits will provide a positive indication that hot water once existed near the Martian surface," Christensen said.
Christensen also said it makes a region of about 300 square miles one of the best places to look for evidence of life on Mars.
NASA officials said the finding implies water was once stable at or near the surface and that Mars had a thicker atmosphere in its early history, probably 4 billion to 6 billion years ago.
Water cannot exist on the Martian surface now because the atmosphere is too thin, and it would immediately evaporate.