Meanwhile, back on Mars...

While robotics experts prepare for their next assault on the Red Planet, there are still two rovers—Opportunity and Spirit—doing their thing on Mars. Incredibly, they’ve endured two Earth years beyond their original three-month mission; despite some problems, including mechanical problems with Opportunity’s robotic arm and one of Spirit’s wheels, and a glitch in one of NASA’s Deep Space Network tracking stations, they show no signs of stopping. Exploring opposite sides of the planet, the robots have continued to gather evidence, captured in more than 125 000 images beamed back to Earth, that ancient Mars experienced periods of wet and possibly even habitable conditions.

IMAGE: NASA/JPL-Caltech/Cornell

Each six-wheeled, solar-powered robot, about the size of a golf cart, carries several scientific instruments, including minispectrometers, a rock abrasion tool for drilling shallow holes into rocks, stereo CCD cameras for capturing panoramas, and another camera for taking detailed images of the ground.

The Mars bots get their driving instructions from operators back at the Jet Propulsion Laboratory, in Pasadena, Calif. Progress is slow—on a typical day, each rover may move only a few tens of meters. As of January, Spirit’s odometer stood at a little more than 6 kilometers, while Opportunity had trekked about 6.5 km. Their Chilean descendant, Zoë, by contrast, can cover that distance and more in a single day and can operate autonomously. And while the Mars machines are designed to study the planet’s geology, Zoë is more a biologist, looking for signs of microscopic life.

Still, the Mars robots’ longevity is impressive. At press time, Spirit [see photo] was rolling down from the summit of 82-meter-high Husband Hill, which it succeeded in scaling last August, and Opportunity was creeping toward a large depression known as Victoria Crater.

—J.K.