Phoenix Touches Down: Photo by NASA/JPL-Calech/University of Arizona

Setting a spacecraft down on Mars isn't exactly easy—just ask Beagle 2. NASA's Phoenix Mars Lander, en route and due for a May 25 rendezvous with the surface, recently received a course adjustment from mission planners as they try to ensure that the craft doesn't drop down in a danger zone.

According to NASA, researchers have found loads of rocks in Phoenix's potential landing area that are big enough to pose a threat. If the lander hit one of these during its final descent, the mission could be over.

Thankfully, though, the Mars Reconnaissance Orbiter has been passing over the region, gathering high-quality images. NASA scientists have been sifting through these images to find the safest spots, and they adjusted the spacecraft's flight path accordingly, firing its thrusters for about 35 seconds.

Eventually, in the last few minutes of its flight, the lander will slow down from 13,000 miles per hour to about 5 miles per hour and, ideally, land softly on its three legs. And no, that's not a simple job, even for NASA. "Landing on Mars is extremely challenging. In fact," says Doug McCuistion, director of NASA's Mars Exploration Program at NASA Headquarters in Washington. "There's no guarantee of success, but we are doing everything we can to mitigate the risks."