A Robot Rolls On The Red Planet

ON JULY 4TH, AS INDEPENDENCE Day parades were winding down on the East Coast, NASA's Pathfinder probe was heading for a landing on Mars in the Ares Vallis, an ancient floodplain. The $200 million vehicle, launched last December, was set to become the first spacecraft to touch down on the Red Planet since two Viking probes landed there in 1976. It won't be the last.

NASA has a whole series of Mars missions in the works, including a satellite due to arrive in September. The program stretches through 2005. That's when scientists may finally get their hands on the first rocks from another planet--which could settle the issue of whether there is, or ever has been, life on Mars. The landings coming up in 1998 and 1999 were planned before last summer's claim that microfossils had been found in Martian meteorites, so those probes won't collect rocks. The missions scheduled for 2001 and 2003 will, but NASA doesn't plan to fly the rocks back right away.

Pathfinder's timetable called for it to greet the Martian sunrise at 5 p.m. EDT July 4 by blinking open its two eyes--dual camera lenses for taking 3-D pictures--and hunting for the sun. Then it can orient its antenna properly for communications with Earth. After mission controllers ran checks on Pathfinder's systems, they planned to tell Sojourner, a file-drawer-size robot vehicle, to get its six wheels rolling and try the Martian soil. If all went according to plan, the first pictures were slated to be on TV around 8 p.m.

The Pathfinder lander is mainly an automated weather station. It was to sample the Martian atmosphere on the way down, then take regular readings in coming weeks of wind speed and direction with a small wind sock. Airborne dust will also be measured, and the camera will track clouds and analyze humidity, using special filters sensitive to water vapor.

Other filters will snap over the twin lenses to peer beneath the skin of Martian rock outcroppings--satellite remote-sensing technology brought down to the surface. This will help scientists decide where to send Sojourner. The wheeled robot carries an alpha-proton X-ray spectrometer (APXS) that can detect even trace amounts of minerals and other elements, including carbon and oxygen. The APXS bombards a rock or patch of soil with alpha particles, generating X-ray and proton emissions that reveal chemical composition.

All this technology stems from a far-flung international collaboration. For example, Pathfinder's $6 million camera system was developed by a team of 40-odd U.S., German, and Danish scientists headed by Peter H. Smith at the University of Arizona's Lunar & Planetary Laboratory. "Light," he says, "just turns me on."

Smith, an optics expert, is now working on a microscope camera for Sojourner's successor. It should furnish more clues to help unlock the secrets of our mysterious red neighbor.