Mapping Mars

So many probes have been taking pictures of the Red Planet lately that it's easy to be jaded--but that wasn't the case last week, when not one but two missions reached a major milestone. On Mars, the Opportunity rover, which has been tooling across the landscape for more than 10 times its originally designed lifetime of 90 days, began taking close-ups from the edge of Victoria Crater, blasted by an ancient impact. Opportunity may soon descend into this hole to study layers of exposed Martian rock for clues to the planet's past.

At the same time, a brand-new probe called Mars Reconnaissance Orbiter began its mission to map Mars' surface with unprecedentedly sharp-eyed cameras, ground- penetrating radar and other instruments. The cameras are so powerful that they can actually see Opportunity, which is about the size of a golf cart, from nearly 200 miles up. They can also help find safe routes for the rover. But more important, they will give scientists a map of Mars that will make future exploration--ultimately by humans--much easier to plan.