The durability of the Mars rovers has been nothing short of staggering. Kids who weren't even born when they were launched have now started Kindergarten. When they landed in 2004, Ars didn't even have a dedicated science section—and wouldn't for over another year. NASA's cautious estimate was that the rovers would be able to travel a kilometer; they're now so confident, that they've started Opportunity on trip that will take several years and cover nearly 20km. Still, all good things must come to an end, and Opportunity's twin, the Spirit rover, has now reached the end of its traveling.

Spirit has been operating with only five of its six wheels for years, but about ten months ago, the remaining wheels wound up stuck in some soft, sandy material; another wheel died recently. After several attempts to free it, NASA has now decided that it's best to simply orient it to soak up as much sun as it can during the Martian winter. The cold and reduced sunlight mean that it'll be much harder to keep Spirit active over the winter, which may send it into a hibernation mode for many months. Winter temperatures will be close to the design limits of the rover's electronics, so there's a chance it won't revive when spring returns to its hemisphere on Mars.

Assuming the rover survives, NASA plans on using it for two experiments: long-term monitoring of changes in nearby soils, with the possibility of detecting some sort of water cycle, and providing fine-grained positional information that will allow researchers to detect wobbles in Mars' rotation, which can be used to infer details of the planet's interior. Neither of these was possible when six functional wheels gave its handlers "the imperative to drive it," as one of the team leaders put it.

That imperative is still very much in effect when it comes to Opportunity, which is on its way to the Endeavor crater, about 19km away from the previous crater that it had explored. On its way, it seems to have found an unusual rock, which is going by the name of "Marquette Island." This rock appears to be a basalt, formed by the slow cooling of molten rock within the crust and then blasted to its current location by an impact. It's the first of its sort to have been observed, and researchers are excited about the data obtained after Opportunity drilled into its interior.