Spirit and Opportunity
Like the Mars Pathfinder Sojourner rover before them, the Mars Exploration Rovers, Spirit and Opportunity, traveled a long way to get to the Robot Hall of Fame.
The twin rovers, launched separately, traveled millions of miles to land at two widely separated sites on Mars in January 2004. The mission — to study rocks and soils in search of clues to the history of water on the planet — was originally scheduled to last 90 Martian days. The rovers each were expected to travel a total of a kilometer.
Both far exceeded those initial goals. Despite dust storms and cold, long winters, the rovers continued to function for years as NASA repeatedly extended their mission. Spirit faced the harshest conditions and suffered from a disabled wheel and accumulated dust on its solar panels. Still, it drove 7.7 kilometers before getting hopelessly mired in soft soil in 2009. It continued to serve as a stationary research platform until NASA lost contact with it in 2011.
Opportunity had lost motion in some of the joints of its robotic arm, but was still operating as of September 2013. By then, it had trekked more than 38 kilometers.
Each of the six-wheeled rovers was about the size of a golf cart and weighed more than a ton. They were equipped with panoramic cameras that could determine the mineralogy, structure and texture of the terrain and sent back high-resolution images of the Red Planet that dazzled earthlings. They also were equipped with spectrometers, microscopic imagers and a tool for scraping rocks to expose fresh surfaces.
These robotic geologists uncovered a wealth of scientific findings. Notably, they found evidence that dry, barren Mars once was a lot wetter than it was today. Discovery of an ancient hydrothermal system raised the possibility that conditions once might have been suitable for sustaining life.