At 8:15 p.m. Pacific time on January 3, the Spirit rover, tucked inside its protective capsule, separated from its interplanetary mother ship and prepared to enter the atmosphere of Mars. For weeks, mission engineers and scientists had been listing in grim detail everything that could go wrong. Explosive bolts might not blow on time; strong winds might slam the capsule against the ground; the lander might settle with its nose down, wedged helplessly between rocks; radio links might fail. As the final days ticked by, a dust storm on the planet erupted, reducing the density of the upper atmosphere. To compensate, controllers reprogrammed the parachute to deploy earlier. Eight hours before the capsule's entry, deputy mission manager Mark Adler said, "We're sending a complicated system into an unknown environment at very high speed. I feel calm. I feel ready. I can only conclude it's because I don't have a full grasp of the situation."

This candid doom-mongering was reassuring. If the team had said there was nothing to worry about, it would have been time to start worrying. Between 1960 and 2002 the U.S., Russia and Japan sent 33 missions to the Red Planet. Nine made it. By the standards of planetary exploration, the failure rate is not unusually high: of the first 33 missions to the moon, only 14 succeeded. But the blunders that damned the Mars Climate Orbiter in 1999--neglecting to convert imperial to metric units, then failing to diagnose the error when the spacecraft kept drifting off course--are hard to live down. And just a week before Spirit reached Mars, the British Beagle 2 lander bounded into the Martian atmosphere never to be heard from again.

   
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