When the robot rover Spirit landed on the surface of Mars six years ago, it was supposed to be on a short-term mission. Designed for 90 days of rolling and rambling amid the dust and cold of the Martian surface, Spirit survived 20 times longer than its warranty allowed.
This week, NASA pulled the plug on Spirit's mission after the robot spent a year stuck in one spot. The space agency had no choice: Spirit didn't phone home after a long winter in frozen silence.
Its circuitry and solar-panel array were too damaged from the cold to revive the six-wheeled rover from its slumber. Spirit was willing, but its battery was weak.
Like the rover Opportunity, which is still operating on the other side of the planet, Spirit transmitted images of the Martian surface to NASA's Jet Propulsion Laboratory during its heyday. The rover also conducted rudimentary analysis of the frozen dirt it extracted.
Spirit's work was incremental and detail-oriented. It traveled nearly five miles beyond its landing site after crawling out of a crater. Spirit also scaled a mountain.
Meanwhile, Opportunity continues to send valuable data about the Martian surface to Earth, with no sign of powering down anytime soon. It eventually will be joined by a next-generation rover called Curiosity, a nuclear-powered robot that launches in November.
As robot rovers go, Spirit will always remain first among equals for what it did with fewer resources. Thanks to Spirit and Opportunity, we know what to expect when a manned space flight goes to Mars in two decades. Spirit was small, but it greatly expanded our horizons.