Last we had heard from NASA's scrappiest Martian robot, the Spirit Rover was stuck, broken, and a few months into a season-long wait for sunlight, when it would try one last time to coax its systems back to life to resume work, albeit without any mobility. Its mission, which had dragged on 25 times longer than expected, had worn on the rover, and scientists were unsure if would ever awaken.
This is still true, and the Spirit still sleeps.
But even in (near) death, the Spirit finds (indirect, potential) signs of life. A report in the Journal of Geophysical Research by deputy principal investigator for Mars rovers Ray Arvidson, and 36 others, flags some of the Spirit's last transmissions before it shut down as evidence of water flowing under the planet's surface.
The ground where NASA's Mars Exploration Rover Spirit became stuck last year holds evidence that water, perhaps as snow melt, trickled into the subsurface fairly recently and on a continuing basis.
Stratified soil layers with different compositions close to the surface led the rover science team to propose that thin films of water may have entered the ground from frost or snow. The seepage could have happened during cyclical climate changes in periods when Mars tilted farther on its axis. The water may have moved down into the sand, carrying soluble minerals deeper than less soluble ones.
The seeping mineral in question, ferric sulfate salt, is actually to blame for causing the Spirit to become stuck in May of 2009. In fact, the soil composition around the site has been broadly described as "bizarre" by NASA researchers, prompting them to assign the Spirit--pending its rise from the dead--one last mission, converting it into a stationary soil analysis lab.
This revelation is a reminder that ensuring smoother operation of NASA's various probes and rovers is only half the battle. These instruments transmit a tremendous amount of data, much of which can be quite opaque and difficult to decipher. This most recent paper, for example, drew on over two years of photographic and instrumental data from the Spirit from a period of several years, ending over seven months ago.
In that sense, even if the Spirit doesn't blink to life after the Martian thaw, its contributions to science will continue for years to come.
Image of Spirit site courtesy of NASA