03/12/1998 08:00:00

Mars Global Surveyor already bringing in scientific payoff

PASADENA—Despite a 12-month delay in aerobraking into a circular orbit, the Mars Global Surveyor is already returning a wealth of data about the atmosphere and surface of the Red Planet.

According to mission scientist Arden Albee of the California Institute of Technology, all scientific instruments on the Mars probe are fully functioning and providing good data. Early results from data collected during the 18 elliptical orbits in October and November are being reported in this week's issue of Science.

"For the first time, a spacecraft has captured the start of a major dust storm on Mars and has followed it through its development and demise," Albee says. "Also, we've received a number of narrow-angle high-resolution images that are enough to put any planetary geologist into a state of ecstasy."

These accomplishments are especially noteworthy when considering that the probe developed a glitch when it first began tightening up its orbit last September. For various reasons having to do with design and cost, Global Surveyor was set on a course that took it initially into a huge sweeping elliptical orbit of Mars.

On its near approach in each orbit, the probe was to dip into the upper atmosphere of Mars in a maneuver known as "aerobraking," which would effectively slow the probe down and eventually place it into a near-circular orbit.

But a solar–panel damper failed early in the mission, and damage to the solar panel forced the team to slow down the aerobraking. At the current rate of aerobraking, Mars Global Surveyor will enter its circular mapping orbit in March 1999.

This has delayed the systematic mapping of Mars, but Albee says that the new mission plan nonetheless permits the collection of science data in a 12-hour elliptical orbit, from March to September of this year.

"Another exciting discovery is that the Martian crust exhibits layering to much greater depths than would have been expected," Albee says. "Steep walls of canyons, valleys, and craters show the Martian crust to be stratified at scales of a few tens of meters.

"At this point, it is simply not known whether these layers represent piles of volcanic flows or sedimentary rocks that might have formed in a standing body of water," he adds.

The Mars Global Surveyor team has previously announced that the on-board magnetometer shows Mars to have a more complex magnetic field than once thought. Of particular interest is the fact that the magnetic field was apparently once about the same strength as that of present-day Earth.

Many experts think that a strong magnetic field may be crucial for the evolution of life on a planet. Without a magnetic field, a planet tends to have any existing atmospheric particles blasted away by cosmic rays in a process known as "sputtering."

And finally, the Mars Orbiting Laser Altimeter (MOLA) has already sent back 18 very good topographic profiles of the northern hemisphere. "Characterization of these features is leading to a new understanding of the surface processes of Mars," Albee says.

Written by Robert Tindol