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US Spacecraft Sees Changing, Dynamic Mars

The planet Mars is giving scientists some new surprises. A U.S. spacecraft orbiting the Red Planet has shown that despite its barrenness, it is not a static place. Instead, its face is changing, possibly because of quakes and global warming. A picture is emerging of a world that is still evolving and might yet be warm enough for certain types of primitive life.

A series of photographs from the U.S. Mars Global Surveyor satellite, in orbit since 1997, shows that the frigid, desolate planet nearest Earth is far from dead. The chief scientist for the U.S. space agency's Mars exploration program, Michael Meyer, says the pictures reveal that our solar system neighbor shares some of the geological activities seen on our planet.

"What the Mars orbiter camera has revealed from a long, detailed study of the Red Planet is a dynamic Mars, a planet that can change, not on the mind boggling [scale of] millions and billions of years, but on the order of years and decades," he said.

The story is told in part by boulders tumbling down a hill and leaving tracks not there just two years ago. The man whose company built the orbiter's cameras, Michael Malin, says the rock falls could signify marsquakes never before detected.

"On Earth, there are a number of processes than can operate to cause boulders to fall down from slopes. Earthquakes on Earth generally stimulate rock falls, strong winds, heavy rains. We know those were not going on Mars, but seismic activity would be my guess and that would be the first evidence we have of anything like that," he explained.

Brown University Geologist Jack Mustard says occasional ground tremors are not unimaginable on Mars. He points out that if marsquakes do occur, they could mean that molten and moving underground processes are generating enough heat to support simple life forms beneath the surface.

"If it's still warm enough to have movement in its interior, that could allow us to contemplate that volcanism might still be occurring and that would relate to the possibility of sustaining habitable environments in the deeper regions of Mars," said Mr. Mustard.

On the outside, Mars appears to be warming. Michael Malin says the U.S. spacecraft images show that the south pole's carbon dioxide ice cap is shrinking about three meters a year.

"The significance of this is that Mars is experiencing climate change, because the present conditions are not conducive to the formation of all this CO2 to begin with in the polar region. So sometime in the distant past, Mars was colder than it is now to form a permanent CO2 deposit. Subsequent to that, it has warmed and we are seeing that earlier deposit being eroded away," added Mr. Malin.

Mr. Malin says no one knows why Mars is warming, but melting carbon dioxide frost could also be the cause of the new gullies that have formed in Martian sand dunes in the past three years. Melting CO2 would slide down the dune and take with it sand that would carve the channels. The scientists say the frost is unlikely to have been water ice, because melting water would have sunk into the sand before flowing downhill.

The Global Surveyor spacecraft that took the images is the oldest of the five U.S. and European orbiters circling Mars. It is the one that identified a surface mineral known to form in water, causing the U.S. space agency to send one of its two rovers now on the surface to do more investigating. Last year, the rover's tracking of the mineral led geologists to suggest Mars once had a shallow salt water sea, considered a condition conducive to life.

How much longer can the Global Surveyor operate? Michael Malin says says it has exceeded its primary mission, but is still a valuable scientific tool.

"We were really impressed that the vehicle has lasted eight years," he noted. "There are a few limiting factors -- propellant for attitude control. Right now, that is projected to last well into the next decade. There are moving parts, and there are some other things that might wear out, some electronic parts. But for now, almost all of those point to an ability to continue to take high quality observations through 2010 and beyond."

In the meantime, the bigger, more capable U.S. Mars Reconnaissance Orbiter is on its way to a March arrival at the red planet. It is designed to survey the surface and sample the atmosphere in much finer detail than the satellites now there.