MARS ROVER HALL OF FAME

by Robert Lamb, HowStuffWorks.com

Spirit

Seven years after Sojourner's demise, NASA had come to expect a good bit more from its latest breed of Martian rovers. On Jan. 4, 2004, the six-wheeled Spirit rover arrived on the Red Planet, just three weeks ahead of its Mars Exploration Rover (MER) twin.

Scientists hoped to use it for a whopping 90 sols (the Martian day, which is 37 minutes longer than an Earth day). As of June 2009, however, the little bot is still ticking.

This impressive boost in lifespan was due to "cleaning events" -- the unexpected clearing of dust from the rover's solar panels. Spirit's designers had originally predicted that, after 90 sols, accumulated dust would prevent it from absorbing necessary sunlight. As it turned out, a little atmospheric disturbance here and there is enough to clean things out and provide a boost in solar power.

Of course, no matter how lucky Spirit is, all those years of exploration have taken a toll. After 779 sols, a busted wheel forced NASA operators to drive the rover backward. Plus, software glitches have knocked it out of communication with Earth for as much as 24 hours at a time.

As of June 2009, the rover was still stuck in some soft Martian soil, but otherwise functional.

Spirit has collected a great deal of data about Mars' possibly warm, wet past -- and its setbacks have even proved advantageous. While driving backward and dragging a wounded wheel has hampered the mission, it has also worked as a useful excavation tool.

Image: Artist impression of Spirit on Mars. Credit: NASA

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