© Geological Society of AmericaSmall rocks, known as clasts, are spaced evenly apart rather than being clumped together in this Spirit rover image of the plain around Mars's Lahontan Crater. The image shows a region of terrain about 50 cm wide.
Photos from NASA's Spirit rover show small rocks spaced so evenly on the surface that it seems as if they must have been carefully arranged by order-loving Martians. But with no evidence of extraterrestrial landscapers, what could have created the pattern?
The wind did it, but not in an obvious way, says Jon Pelletier of the University of Arizona.
Wind storms and dust devils rage across Mars, so it's logical to suspect they blew the rocks. But the Red Planet's atmosphere is so thin that winds would have to be "10 times Hurricane Katrina" to pick up the stones, Pelletier told
New Scientist. And wind-blown rocks would have no reason to stop where they were nearly equidistant from their neighbours.