Marking Its Territory: This 'bot projects light at various wavelengths-in this case, green-while taking photos. If a key organic molecule is present, it will glow and show up in the photos. John B. Carnett

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When we catch up with the robot, it is poking along in a herky-jerky and rather flummoxed fashion through the Atacama Desert, which covers much of far northern Chile. The Atacama is reputedly the driest place on Earth, with rainfall measured in millimeters per decade. It is a rough place for man or robot, a tawny maze of high plateaus and shaley foothills under constant sun and an enormous cobalt-blue sky. And so here is where a group of engineers from Carnegie Mellon University have come to test their creation, a six-and-a-half-foot-long, 440-pound robot built to detect life in seemingly lifeless environments. The robot features a cutting-edge system for identifying organic molecules, but it looks less than high-tech, more like a robotic patio table built with spare bicycle parts. And although its knobby wheels can soak up flat terrain at a brisk human walking clip, right now it´s in trouble.

"Ah, that´s the angle of refusal," says Carnegie Mellon roboticist David Wettergreen. The robot-named Zo, the Greek word for "life"-had been making its way up a steep ridge, but suddenly its navigation software called for a complete stop. Zo is stranded on an impassable slope of rock and sandy dirt. A discreet 100 yards away, two young engineers are sitting in the cab of their 4x4 tapping away at Dell laptops, accessing Zo´s sensing software over a shared wireless network. On their screens, they see the world as the robot does, a field of black, white and gray tones; the whiter the terrain, the steeper, the higher-the better to avoid. There is a lot of white.

Wettergreen plugs a cable into the robot to temporarily switch to manual control. At his end of the cable there´s a joystick-like lever that he uses to steer the ´bot around the worst of the steep bits-to all appearances, a man walking his supersize dog. Chris Williams, a Carnegie Mellon mechanical engineer who, along with Wettergreen, has been trudging beside Zo, shares robot-
wrangling duties. "It´s my hours of work I´m going to lose if she falls off something," he says.

It´s no wonder that Wettergreen´s team dreads trashing the machine they´ve invested 18 months of their lives to assemble. But Zo´s ability to navigate autonomously is just one half of this mission. NASA, the project´s underwriter, wants to see if Zo can perform scientific tasks for a team of geologists and biologists who are managing it remotely from Pittsburgh, 4,900 miles away. A life-seeking mission to Mars is planned for sometime around 2016. If all goes well in this test run, a techno-descendant of Zo will be onboard.

But here on Earth this October afternoon, in terrain that´s about as similar to Mars as one can find, the programmers share a look of dismay. This morning, when they inputted Zo´s daily mission plan, they had their doubts. Now that they´ve gotten an up-close look at the hills and drainage channels it´s supposed to be driving through, they´re convinced. The scientists in Pittsburgh who tell Zo where to go have lost their collective minds.