Surface of Mars still shifting, pounded / Years of images show planet's surface in constant change, regularly hit by asteroids
Published 4:00 am, Wednesday, September 21, 2005
Sere and silent Mars is no dead planet, but in many ways its surface is dynamic and ever-changing, with gullies actively forming, rocks tumbling and asteroids blasting fresh craters in the sand, new images released Tuesday show.
Even the planet's climate appears to be changing -- perhaps indicating that Mars, like Earth, is undergoing a period of global warming, said scientists interpreting the images.
The pictures, taken by high-resolution cameras aboard the 8-year-old orbiting Mars Global Surveyor spacecraft, "reveal a planet that can change not only in the mind-boggling millions or billions of years, but on the order of merely years or decades," said Michael Meyer, chief scientist of NASA's Mars Exploration Program in a teleconference Tuesday from the Jet Propulsion Laboratory in Pasadena.
They show the gullies perhaps caused by frozen groundwater, the results of rockslides from what could have been "marsquakes," and the fresh craters probably created by bombarding asteroids from above.
Activity on Mars "is still continuing and showing a dynamic surface with Martian processes still in action," said John F. Mustard, a Brown University geologist.
Fresh gullies, hundreds of yards long and tens of yards wide, have formed in sand dunes within the past three years, said Michael Malin, whose company, Malin Space Science Systems of San Diego, built the cameras and monitors their output every day. They may well be caused by liquid carbon dioxide saturating the sands and triggering the flows, but it's quite possible that water ice or melting ground frosts could also be carving them, said Mustard.
Malin's images (www.msss.com/others/preview12Sept05release/) reveal long crater slopes where rocks have fallen down, dislodged from the crater rims by unknown forces. They maybe have been tumbled downward by strong Martian winds, he said, but just as likely is the possibility of seismic activity.
Mustard said the possibility of marsquakes is real, as the ancient planet is still evolving and heat continues to be released from radioactive rocks deep in the Martian interior. That heat, he said, could well create tectonic stresses beneath the planet's surface that would be released in seismic movement. Seismometers placed on the moon by the Apollo astronauts detected "moonquakes" on that supposedly dead orb, he said. So, why not on Mars?
In 1976, NASA's two Viking spacecraft made history's first Mars landings in search of evidence for life. They carried seismometers, but they failed to work. Now, the European Space Agency is considering a fleet of small spacecraft that would deploy a network of seismometers on the planet. Scientists like Mustard are eager for that project to fly, he said.
Cameras aboard the Mars Global Surveyor also found five or six fresh impact craters on the Martian surface, Malin reported, and although the orbiting spacecraft has covered only 4 percent of the planet, there are probably hundreds more, he said.
Early in the planet's history, some 4 billion years ago, Mars and Earth and all the other solid planets were subjected to massive bombardments by rocky debris left over from the formation of the entire solar system.
New craters are being formed much more infrequently, Malin said -- most probably when large objects in the asteroid belt between Mars and Jupiter collide, break into smaller rocks and then are diverted to the Martian surface by Jupiter's powerful gravity, he reasoned.
The camera-carrying spacecraft has been surveying the south polar cap of Mars, which is covered deeply by frozen carbon dioxide forming a vast snowbank. But cliffs and "polar pits" on that ice cap are visibly eroding "at a prodigious rate," Malin said -- strong evidence that the planet's climate is warming from its once deeply frozen state. No one can explain why, Malin and Mustard agreed.