Revered Spirit rover landed on Mars a decade ago

Ten years ago Friday, the Spirit rover made an airbag-cushioned landing on Mars to begin a six-year exploration of Gusev Crater, outlasting even the most enthusiastic of prognostications from the mission's engineering and science teams.

Spirit's landing on Jan. 4, 2004, began a decade of unparalleled exploration on Mars, in which scientists learned the dusty world was once warmer and wetter.

Three weeks later, Spirit's twin rover Opportunity landed on the opposite side of Mars to survey a vastly different landscape.

Scientists selected Spirit's landing site in Gusev Crater based on imagery obtained from orbiters indicating the Connecticut-sized basin may have once held a lake. Spirit launched from Cape Canaveral, Fla., on June 10, 2003, on a Delta 2 rocket.

Opportunity ended up in a much richer environment of scientific targets than Spirit, finding multiple strands of evidence supporting the hypothesis that Mars was once wet and habitable. Steve Squyres, the chief scientist for the rovers at Cornell University, made the announcement less than six weeks after Opportunity landed.

It took longer for Spirit to reach scientific pay dirt. Controllers at NASA's Jet Propulsion Laboratory commanded the six-wheeled rover to drive toward a range of peaks named the Columbia Hills in remembrance of the astronauts who perished on space shuttle Columbia in 2003.

"In the Columbia Hills, we discovered compelling evidence of an ancient Mars that was a hot, wet, violent place, with volcanic explosions, hydrothermal activity, steam vents -- nothing like Mars today," Squyres said in a NASA press release.

NASA last heard from Spirit on March 22, 2010, before it succumbed to a Martian winter.

Spirit radioed data back to Earth for more than six years, vastly eclipsing the 90-day duration of its baseline mission. The probe carried a suite of cameras, a robot arm with a tool to grind into rocks, a microscopic imager and several spectrometers to measure mineral composition.

The failure of two of Spirit's wheels left the rover in an unfavorable position for winter. Engineers previously parked the rover on a slope facing the sun to keep the robot powered as sunlight diminished during the cold season, but Spirit was trapped in a sand pit and unable to move.

NASA officials said Spirit's critical components and connections may have been damaged by the cold temperatures, rendering the rover lifeless.

Opportunity is still going strong, having lasted nearly 10 years and traveled 24 miles across the red planet's treacherous surface in a region named Meridiani Planum.

"At Opportunity's landing site, we found evidence of an early Mars that had acidic groundwater that sometimes reached the surface and evaporated away, leaving salts behind. It was an environment with liquid water, but very different from the environment that Spirit told us about," Squyres said.

Opportunity is now on the trail of clay minerals on the rim of Endeavour Crater, a 14-mile-wide bowl carved by an ancient asteroid or comet impact.

"When Opportunity got to the rim of Endeavour Crater, we began a whole new mission," Squyres said. "We found gypsum veins and a rich concentration of clay minerals. The clay minerals tell us about water chemistry that was neutral, instead of acidic -- more favorable for microbial life, if any ever began on Mars."

Officials credit occasional Martian dust devils for the long lives of the rovers, especially Spirit, which had its power-generating solar panels cleaned of dust several times by gusts of wind blowing overhead.

Spirit drove 4.8 miles and snapped 128,000 images with its suite of cameras.

"Because of the rovers' longevity, we essentially got four different landing sites for the price of two," Squyres said.

We present some of our favorite images from Spirit's six-year mission.