Rover ready for overland Martian trek

Wednesday night, as the hours of the West Coast evening drain toward midnight, the sun will rise over the Gusev Crater some 106 million miles away. In the gathering light of a Martian morning, seeping from pale blue to the featureless pink veil of day, the planet's latest visitor will blink to life.

In the 11 days since it hurtled from the sky and came to rest here on the flat and endless fields of russet dust, the cocoon of the Spirit lander has unfurled like a massive metallic flower in time-lapse, spreading its solar petals in anticipation of this moment. Inside, a six-wheeled rover, once pressed low, stands upright, its spindly limbs eager to sample the Martian desert below.

Wednesday night, that could finally happen. If all goes well, Spirit will creep off its perch in the wee hours of the American night, opening a window onto a world that many have known only through science-fair dioramas or textbook photos.

Spirit has already given a glimpse with its panoramic photos. So has Pathfinder, which snapped pictures amid Martian rocks 6-1/2 years ago. But the rover, if it is successful, promises something far more intimate and profound.

It offers the possibility of unraveling the narrative of cosmic creation - a planet's birth and life, its moments of cataclysm and cycles of renewal - not from distant images or mathematical inference, but by sifting evidence from the planet itself.

For the first time, scientists get to play geologist in extraterrestrial dust with an array of gadgets that would make James Bond blush. At most, the results could fundamentally alter our understanding of organic life. At the least, it will reveal a more vivid picture than has ever been seen of a planet where mountains soar to 80,000 feet and temperatures can drop 150 degrees F from your toes to just above your head.

"Mars ceases to be a light in the sky, and it becomes a place," says Robert Zubrin, president of the Mars Society.

There still is a chance the rollout could be delayed. Monday and Tuesday nights the rover was expected to perform a 120-degree pirouette on its platform. The maneuver is necessary because the edge of one deflated airbag is obstructing the ramp directly in front of the rover. Turning will give it a clear exit on a different ramp.

At the bottom of the ramp lies a land in some ways familiar. Wisps of water clouds can glide high overhead. Fog gathers in the low-lying valleys and canyons until driven off by the rising sun. And on rare occasions, settling dust can leave patches of bluish sky above the Martian horizon.

Yet the world in which Spirit now survives is at the same time inhospitable beyond imagination. Its atmosphere is less than 1 percent of Earth's, meaning that any liquid immediately turns into gas.

At the poles, carbon dioxide falls as snow in frigid temperatures. At the equator, surface temperatures can reach 80 degrees F, but the tenuous atmosphere means that temperatures drop to minus-70 degrees F 10 feet off the ground. And it means that dust is blown everywhere. Though fierce winds would only feel like brisk breezes in the thin atmosphere, they lift so much dust off the ground that the sky normally glows a dull salmon pink. Dust storms, likely kicked up by tides of solar heat, can blot out an entire hemisphere.

"The atmosphere causes all sorts of things to be very different," says Bruce Betts of the Planetary Society here.

Indeed, Mars is a world of extremes. The extinct volcano of Olympus Mons far away rises more than 80,000 feet above the Martian surface, covering an area the size of Arizona, and, in places, falling nearly 20,000 feet in sheer scarps. Near it, volcanic activity early in the planet's life pushed a North America-size land mass six miles above the surrounding plains.

The action was so violent that scientists believe it ripped a scar in the planet's crust, called Valles Marineris, which is several times deeper than the Grand Canyon and could stretch from New York to Los Angeles. Near the north pole, dune fields ripple across the landscape in a rusty Martian Sahara. "It's a geographic wonderland," says Michael Carr, an astrogeologist at the United States Geological Survey.

Likewise, Gusev Crater is a testament to the the Red Planet's extreme character. Just south of the equator, it stretches 95 miles from rim to rim and is so wide that Spirit, from its seat somewhere in the middle of the crater, can see no hint of the edge - only small hills more than a mile distant.

Some 30 miles south of Spirit, the great cleft of the Ma'adim Vallis empties into the crater. Scientists have theorized that perhaps billions of years ago, this 550-mile-long, 16-mile-wide trench brought floods of water into Gusev, putting Spirit on the bed of an ancient lake. That's why Spirit is here - for clues to the past presence of water, and perhaps primitive life.

For at least 90 days, Spirit will scuttle along, covering an estimated 65 feet a day, grinding down rocks to analyze their older innards and snapping infrared photos for signatures of water.

What it finds on the barren landscape will help write the story for Mars' unknown history. Was the planet a warm and wet place of lakes and rivers? Or was some other mechanism at work on a planet not too different from the one of today?

Says Dr. Carr: "All these little pieces add up to a clearer picture of what happened in the past."