Even though Mars’ atmosphere is only about 1 percent as dense as Earth’s, there’s still enough air to whip up whirlwinds known as dust devils. NASA’s Mars Global Surveyor has tracked the mini-tornadoes from orbit, but they’ve never been spotted from ground level. Until now. Last week, after more than a year of watching, the Spirit rover captured a couple of wisps making their way across the desolation of Gusev Crater, said a member of the rover science team, Geoffrey Landis of NASA’s Glenn Research Center. “In some of the navigation camera images, we actually spotted two dust devils, and one of those dust devils was visible in the rear hazcam,” Landis said.