Return To Mars

By Jeffrey Kluger

It's a safe bet the herd of deer that wandered onto the grounds of NASA's Jet Propulsion Laboratory (J.P.L.) in Pasadena, Calif., last week had no idea what was going on when a team of scientists burst into a courtyard, cheering and high-fiving over the successful landing of the Spirit rover on the surface of Mars. If the deer wander back this week, they could see more of the same, that is if Spirit--which has been operating splendidly but has not yet budged from the safety of its landing platform--at last rolls cautiously down onto the red Martian soil, preparing for three months of rambling the alien terrain.

By almost any measure, it was a spectacular week both in Pasadena, where the rover was birthed, and at Gusev Crater, Mars, where it now finds itself. NASA has been in need of redemption since the explosion of the shuttle Columbia last winter, and Spirit--to say nothing of its sister ship, Opportunity, heading for its own Martian touchdown at the end of the month--is it. The space agency's website recorded 1.45 billion hits in just over five days last week. The White House, perhaps sensing an election-year winner, announced that the President would soon deliver a long-delayed speech about the future of the space program, possibly including a return to the moon and a manned trip to Mars.

The real news, however, was made on the Red Planet. The 90-mile-wide Gusev Crater--located about 15DEG south of the planet's equator--resembles a dry lake bed, one that could easily have been drenched with water from what appears to be a 559-mile-long river channel entering it from the southeast. If there was once Martian water, it should have ponded there. If there was once Martian life, it might have called this great lake home.

That possibility, plus Gusev's relatively smooth, obstacle-free terrain, is why the crater presented such a tempting target--and why NASA scientists are so thrilled that the spacecraft made it. "If you were looking for a place to land in the U.S., geologists would land in the Grand Canyon and engineers would land [in a plain] like Kansas," says paleontologist Andrew Knoll, a member of the rover long-range-planning team. "Gusev gives us both a congenial site for roving and still has a high probability of getting to good outcroppings."

Before Spirit can actually start to dig in the Martian sandbox, however, there are a few technical obstacles to overcome. Last week, mission managers discovered a worrisome spike in temperature within the guts of the rover during the Martian daytime, requiring them to periodically power down some instruments to give the machinery brief cooling naps. An electrical surge in the main antenna also caused concern, but so far it appears to have been a harmless hiccup.

More challenging is a problem with the landing platform--something that could interfere with Spirit's very ability to move. The rover descended to the surface in a hard, three-petaled shell that was protected by the now famous swaddling of air bags. On the ground, the bags deflated and the petals opened, providing Spirit with three possible exit ramps onto the surface. The problem is, one of the ramps--the best one, as it happens, since the rover does not have to turn around to reach it--is partly obstructed by the collapsed bags.

A maneuver designed to lift the petal and retract the bag failed at the end of last week, and engineers are planning to have the rover exit down a rear ramp. Even if that one proves to be blocked too, it would still be possible to drive over the bags, though that is a risky move since the fabric may have stiffened in the extreme Martian cold and could damage or interfere with the craft's solar panels. In either event, no one at J.P.L. is remotely calling these problems mission-enders--though no one expects the rover to be able to move off the lander much before the end of this week. "We have some very valuable assets on Mars," says J.P.L. director Charles Elachi. "Now is the time to be careful."

Whenever Spirit finally starts to travel, it will have no shortage of targets. The vehicle's nine cameras have been drinking in images of the surrounding terrain and beaming them back to Earth in brilliantly sharp resolution, sometimes even in 3-D. Every day six teams of J.P.L. scientists gather in a large, classroom-like office to study the pictures on several 6-ft.-wide projection screens, smaller laptop-size screens and flat electronic slates. What they have found has intrigued and in some cases mystified them.

Perhaps the most interesting spot on the surface is one the spacecraft created. As the bubble-wrapped craft bounced to a landing, it scuffed the ground at a point just south of where the rover now rests. The loose red soil it cleared away has revealed a dark patch of what resembles mud--though that's impossible on the entirely waterless floor of Gusev.

"It looks like mud, but it can't be mud," says Steve Squyres, the mission's principal science investigator. "It holds together well. I'm not even prepared to speculate."

One possibility is that the soil, while now dry, was once wet. Water rising to the surface or sinking down from above could have caused the dirt to congeal, perhaps leaving salty deposits that help hold it together. The Viking probes investigated similar-looking callused patches back in 1976. Investigators on those missions dubbed the features duracrust. The science team working this trip is eager to dig around in the stuff.

The duracrust gave new relevance to a study published in 2000 by microbiologist Russell Vreeland of Pennsylvania's West Chester University. Vreeland discovered some 250 million-year-old salt crystals in New Mexico that contained tiny quantities of ancient water. The water held preserved spores that sprang back to life once their salt and nutrient levels were adjusted. Whether this is possible in the punishing, radiation-soaked environment of Mars is hard to say, but it certainly makes anything that hints at salt worth a closer look.

A scattering of small craters within the larger Gusev Crater are attractive to mission planners as well. Such secondary-impact pits do geologists' excavation work for them, gouging away upper layers of soil and rock and offering a free peek at what lies below. There appears to be an especially inviting population of small craters to the east and southeast of the rover, providing one more reason for Spirit to head that way when it dismounts. "We've got a capable machine, but we can't dig 20-ft. holes with it," says Squyres. "The way to do that is to look at one of these craters."

Hills too have caught the scientists' eyes. The far smaller Sojourner rover that landed on Mars in 1997 never moved more than 39 ft. from its home base. But Spirit is built to roam, and its cameras have spotted some inviting, 300-ft.-high mounds nearly 1.25 miles (2 km) away. The robot was designed to travel only about half that distance, but there's nothing to say it can't exceed expectations. Matt Golembek, a J.P.L. geologist, thinks Spirit has a shot at capturing the view from the summit of a mound. "Given how smooth and flat the terrain is," he says, "everyone feels pretty comfortable that that might be someplace we can get to."

One thing Spirit won't have to travel far to explore is rocks. There's a whole quarry's worth of loose samples littering the Gusev floor, possibly carried there by river water or even glaciers. The rover is equipped with a robotic arm that includes two spectrometers for analyzing chemical and mineral composition, a microscopic imager and, most usefully for rock work, a miniature drill. "This thing's like a big Swiss Army knife," says Squyres.

Choosing the rocks most worthy of the attention of all this hardware won't be easy. J.P.L. scientists admit that Gusev Crater looks a little less pristine than they had hoped. Since the time its water vanished, the terrain may have been covered by lava, blasted by incoming meteorites, and then further eroded by millions of years of winds. It will take some doing to find the rocks that have been least affected by all that. Making a choice and then getting to a prize sample could take more than five days. On a mission that may last no more than 90 days, that's a lot of time. "You've got to think hard about where you're going," says Knoll.

Something the scientists do know is that once Spirit has its wheels in the dirt, it's going to act fast. Almost immediately, it will extend its robotic arm and begin sampling the soil directly in front of it. This will allow it both to calibrate its instruments and get the data flow streaming back to Earth. The Apollo astronauts used to do something similar, spending their first moments on the moon collecting what they called a contingency sample--a clump of lunar soil and rock they would tuck into a spacesuit pocket so they would have something to show for the trip if a sudden emergency forced them to turn around and come straight home. Spirit, of course, is never coming home. It will spend its entire useful life on the Martian surface and die there sometime before the end of spring. NASA scientists plan to make sure it makes the most of every day it has. --Reported by Dan Cray/Pasadena

With reporting by Dan Cray/Pasadena