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, and the Mars Pathfinder probe detected them back in 1997. But despite a year's worth of watching, they've never been spotted by NASA's latest rovers — until now.
Last week, 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 told MSNBC.com.
The disturbance is extremely hard to see. "You have to stretch the images to really bring it out, but that’s actually typical of dust devils," Landis said.
It's possible to make out a flare of kicked-up dust in this image if you look at the hazy part of the plain, almost hidden behind a ridge of the Columbia Hills. You can also catch it out on the center of the plain a few minutes later, as seen here. The best way to see it is to flip between images for a "now you see it, now you don't" effect. Daniel Crotty has created just such an animated image, and after watching the picture flip back and forth for a few seconds, you should be able to see the dust devil in the distance.
Landis said wind activity during Sol 420 on Mars — or last Thursday back on Earth — apparently swept some of the accumulated dust from Spirit's power-generating solar arrays. That's fantastic news for the rover mission team.
Over the past year, the dust buildup had reduced Spirit's power output by almost 50 percent. "Now that's suddenly changed," Landis said. "We've seen a couple of huge jumps in power for Spirit. It's improved things quite a bit."
He said Spirit's power-generating capacity bounced back to just 7 percent less than it was at the start of the mission.
Spirit's twin on the other side of the planet, the Opportunity rover, has similarly benefited from periodic sweepings, which are also thought to be due primarily to wind activity. Considering that both rovers are still going strong, long after their expected 90-day lifetime, last week's whirlwinds may not be the last ones caught on tape.
"We're hoping that now that we're starting to spot them, we can see a lot more and build up statistics about how often they occur," Landis said. Close study of the dust devils could provide atmospheric scientists with fresh insights about Martian wind behavior.
NBC News space analyst James Oberg contributed to this report, which was originally posted as a Cosmic Log item March 11. The report was corrected on March 16 to reflect the fact that the Mars Pathfinder probe detected dust devils in 1997, with at least one showing up on a Pathfinder image.