Mars Rovers Keep on Tickin'

In March of 2004, the Mars rovers, Spirit and Opportunity, were expected to last only 90 days and to travel about 600 yards. Remarkably, both rovers have lasted for more than 900 days, and have traveled several miles. The thing that seems to be keeping these rovers going is the way that they are designed to collect and store energy. The rovers each have solar panels; so as long as dust does not collect too much on the panels, the rovers will continue to surprise scientists by lasting many more days and miles. The solar energy not only keeps the rovers moving, but it also heats them up when the nighttime temperatures become too frigid.
At one point, Opportunity got stuck and the researchers feared the worst, only to find that the best method for getting the rover moving again (a tried and true method on Earth) was to put it in reverse and "gun it." So, the rovers have proven to be stronger than ever expected.

http://abcnews.go.com/Technology/story?id=2493314&page=1