The ground where NASA’s Mars Exploration Rover Spirit became stuck in 2009 holds evidence that water, perhaps from melting snow, trickled into the subsurface fairly recently, NASA said in an Oct. 28 press release announcing the findings.

Spirit got bogged down in April 2009 at a site called Troy and spent the rest of the year trying to back out of its predicament before its energy levels fell too low for continued driving. Scientists took advantage of the months Spirit spent at Troy to examine in great detail the soil layers the rover’s wheels had exposed.

NASA says that stratified soil layers with different compositions close to the surface led the rover science team at the Jet Propulsion Laboratory in Pasadena, Calif., to propose that thin films of water may have entered the ground from frost or snow. The seepage, they theorize, could have happened during cyclical climate changes in periods when Mars tilted farther on its axis.

Analysis of the findings appears in the Journal of Geophysical Research.

Spirit landed on Mars in January 2004 and completed its primary mission in April of that year. The rover entered a hibernation mode in March, but with spring beginning at Spirit’s site in November, NASA is using the Deep Space Network and the Mars Odyssey orbiter to listen if the rover reawakens.