Red planet still a mystery, but Mars Global Surveyor makes it less so

Data flooding in from the Mars Global Surveyor spacecraft is showing scientists that a lot of what they thought they understood about the red planet they really didn't understand at all.

That's how geologist Tracy Gregg, of the Univ. of Buffalo, sums up the state of Mars exploration. Dust covers many features of interest. Some of Surveyor's instruments can't show the degree of detail scientists crave. But others, such as the laser altimeter, are precise enough to challenge scientists' assumptions.

That includes a key assumption about one of Mars' most prominent features - the heavily cratered highlands and adjacent relatively smooth northern lowlands. It's been easy to believe the smooth lowland crust is younger than the highlands because it doesn't show the scars from the asteroid bombardment that pummeled the inner solar system in its early years.

Now Herbert Frey and several colleagues find that topography measured by the laser altimeter shows what appear to be more than 600 ancient craters larger than 30 miles in diameter beneath the smooth surface. Those lowlands may have a relatively young overlay. But they believe their findings suggest the crust there is "very, very old." "I've actually been waiting 15 years for this kind of data," says Dr. Frey, who works at NASA's Goddard Space Flight Center in Greenbelt, Md. He adds that such data are "sharpening the image of what was a fuzzy picture of the history of Mars."

His colleague James Head from Brown University in Providence, R.I., puts it more dramatically. He says Frey's work "pushes the reset button" on scenarios of how Mars evolved as a planet. Dr. Head adds that the new data are putting scientists in position to construct a layered profile of the lowland crust. That includes any water-deposited layer on top.

Tracy Gregg showed how the laser altimeter, among other instruments, lets his team trace ancient lava flows farther and more precisely than ever before. For Dr. Zimbelman and his co-investigators, clearer views of the dust itself brings insight. The way dust is distributed on upper regions of some volcanoes convinces them that the winds of Mars blew differently in the past. He said they can't see any way to move that material around under present atmospheric conditions. He called this the "best indication yet of [past] climate change" on the red planet.

(c) Copyright 2001. The Christian Science Monitor