Photos Show Mars Ice Cap Smaller Than Expected

SAN FRANCISCO —  New satellite images providing the first close-up views of Mars’ north pole show it is a thick ice cap wider than Texas but much smaller than previously thought.

Planetary scientists said Sunday that the ice cap revealed by the Mars Global Surveyor is made of frozen water. But even with Mars’ very cold climate, it is only half the size of the ice cap covering Greenland and only 4% of Antarctica’s combined ice sheets.

The amount of water trapped in the ice cap is not sufficient to have carved the deep gullies that scar the surface of the planet, and is far less than the minimum volume that researchers believe would have been necessary to fill an ancient ocean.

The new three-dimensional images were discussed at the American Geophysical Union meeting in San Francisco. The data will be published Friday in the journal Science.

Researchers said the ice cap is unlike any feature they have seen on Earth, or any other orbiting body in the solar system.

It rests in a deep basin at the top of the planet that might have been created by an asteroid impact similar to craters on the moon. The ice cap measures 750 square miles and is 1.8 miles thick.

Mars Global Surveyor is gradually descending into the Martian atmosphere using aerodynamic drag to slow down. Since last summer, it has made over 180 looping orbits around the planet’s poles, passing as close as 80 miles above the ice cap.

Researchers said the new images raise more questions about past conditions on Mars than they answer.

For example, how did the ice cap form? Because the ice cap rests in a basin, it is likely that water on the planet’s surface flowed north from the equator to the pole, they said.

Features apparent in other images of Mars’ northern hemisphere show evidence of ancient springs. These springs may have supplied the additional water required to carve surface features, they said.

“The springs apparently were fed by ground water,” said Michael Carr of the U.S. Geological Survey. “The amount of ice in the cap cannot possibly explain the features that we see. I think the water is there now.”

NASA plans to launch its next unmanned satellite to study the Martian climate Thursday. In January, the space agency plans to launch another spacecraft to study the south pole of Mars.