Closing In on Mars

By Jeffrey Kluger

The launchpads have long since cooled following the lift-off of NASA's two Mars rovers in June and July. But the spacecraft have been pressing ahead. During a summer that Americans spent lazing or working or planning vacations, the twin vehicles, dubbed Spirit and Opportunity, have traveled 137 million miles and 91 million miles, respectively (with 166 million and 192 million more to go), on their way to touchdowns on nearly opposite sides of the Red Planet on Jan. 4 and Jan. 25.

True, you have seen a Mars landing before. Pathfinder's spectacular little rover, Sojourner--a remote-controlled vehicle about the size of a microwave oven--toddled across the Martian terrain in the summer of 1997. But you won't want to miss the show the two new ones promise to put on.

Unlike little Sojourner, Spirit and Opportunity are full-blown Mars cars, about the size of golf carts and fairly stuffed with instruments--including a bristle of cameras atop an almost 5-ft. antenna mast that will provide an eye-level view of the terrain, as opposed to the shin-level view Pathfinder provided. Like their predecessor, they will be visiting areas of the planet that scientists believe were once deluged with water, precisely the kind of spots extraterrestrial organisms would, at least in theory, love. If Mars ever harbored life, the 90 or more days Spirit and Opportunity will spend prospecting in these spots may turn up the geological evidence.

The prospect of the landings could not have come at a better time. NASA was smacked around soundly last week when the long-awaited report on the loss of the space shuttle Columbia was released. Investigators blamed the tragedy, at least in part, on the agency's lack of a crisply defined focus--particularly its largely aimless program of human exploration. But launching interplanetary probes is something NASA has always done well. At the moment, Mars is making itself a decidedly tempting target, and humanity is taking advantage of it.

The planet last week passed closer to Earth than it has in almost 60,000 years. Even as Spirit and Opportunity speed toward their wintertime rendezvous, the European Space Agency has a probe of its own on the way, a stationary lander expected to touch down on Mars on Christmas Day. The Japanese, back in 1998, launched an orbiter, which, after a circuitous route through the solar system, should arrive sometime in December.

Nonetheless, it is Spirit and Opportunity that are generating the most buzz, at least partly because the 6.3 billion of us left behind on Earth will be able to share the trip. As with the Pathfinder mission, NASA will fling open a trio of websites that will track the surface explorations as they unfold. Whatever the spacecraft learn, we'll learn along with them--and it could turn out to be plenty. "We have on these rovers so many capabilities that have never been present on another planet," says Steve Squyres, the missions' principal investigator. "I guarantee you, we're going to find new things."

Even before the spacecraft were launched, it was clear their designers had done an extraordinary job. The rovers will reach the Martian surface much the way Pathfinder did, descending with the aid of rocket engines and parachutes and bouncing to a landing swaddled in air bags. After shaking off its inflatable cocoon, each 384-lb. vehicle will unfold itself into its full standing physique, measuring 5.2 ft. long, 7.5 ft. wide and 4.9 ft. tall.

Both rovers make the most of their size, carrying a full load of instruments, many of them attached to an agile mobile arm. A thermal-emission spectrometer will study background radiation for clues to rock composition; another spectrometer will look for minerals and iron; a third will emit X rays and alpha particles, which will also reveal what rocks are made of. More dramatic, a rock-abrasion tool equipped with diamond-tipped grinding wheels will gouge samples open.

What the rovers will see both inside the samples and elsewhere promises to be considerable. In addition to the four cameras perched at the top of the mast, two in front will help the vehicles go where they need to, and two in back will help them steer. Most impressive, a microscopic imager on the robot arm will do close-up work, squinting deep into rocks to study their texture. "This thing's got eyeballs all over the place," says Squyres.

The rovers, no matter how good their vision is, will have to take things slowly. There will be no scooting from rock to rock when the cameras spot an interesting outcropping. At their fastest, the rovers will move only about 2 in. per second--or about 0.1 m.p.h. And that movement will not take place in anything like real time. Controllers will plan in advance any expedition the rovers attempt, then transmit an entire bundle of instructions, telling them every turn they are to make on the trip. Says Joy Crisp, the project's lead scientist: "In the morning, after each rover has woken up and gotten some sun on its solar panels, we'll send up a set of commands with instructions for what it's supposed to do the rest of the day."

Such plodding travel could yield remarkable science. NASA geologists sifted through 185 possible landing sites for the twin spacecraft, looking for ones that present a minimum of obstacles and a maximum of potential clues to the all important question of whether water has existed on the planet. The rover Spirit is thus headed for a formation known as Gusev crater, about 15-o south of the Martian equator. Orbital photography has mapped a sinuous, 559-mile channel that slices into Gusev from the southeast and looks for all the world like a riverbed. "The water should have cut through that crater and then ponded," says Crisp. Spirit's instruments will scrutinize the crater floor, looking for evidence of lakebed sediment as well as particular minerals that form in the presence of warm water and others that form in the presence of cold.

Opportunity will land on the other side of the planet, 2-o south of the equator on the Meridiani Planum. Scientists are intrigued by this site because infrared mapping by NASA's orbiting Mars Surveyor has detected a mineral known as coarse-grained hematite. On Earth, hematite is a semiprecious stone; on Mars, it could be flat-out priceless. Hematite typically forms where there are lakes and hot springs, both of which could have harbored life. "Hematite is an entirely different kind of water evidence," says Crisp.

Whether or not the scientists have misjudged the sites they have chosen, NASA is betting heavily that it has not misjudged the planet as a whole. Just last month, well before the rovers' scheduled arrival, the space agency announced plans for a stationary lander it will launch in 2007 to Mars' northern polar region, a promising area because it is still rich with water ice.

Before that spacecraft can go, Spirit and Opportunity must first reach Mars, settle safely onto the surface and carry out the missions they were built to perform. Mars Surveyor and Mars Odyssey, launched in 1996 and 2001, respectively, and still at work in Martian orbit, will be waiting for them when they arrive. And all these spacecraft will be joined in their work by the Japanese and European machines. The six-ship holiday convergence will be the biggest team of spacecraft ever sent to study another world. When the new flock is in place, Earth and Mars will be a good 124 million miles apart. But for a while at least, they will seem closer than they have ever been. --With reporting by Dan Cray/Pasadena

With reporting by Dan Cray/Pasadena