What has been moving rocks on Mars?
点击量： 时间：2019-03-09 08:01:02
By Jeff Hecht 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. Inspiration came when his student Andrew Leier described wind-tunnel experiments he had seen elsewhere. If rocks are in a clump, the wind blows dust grains from in front of the rocks to the sheltered area behind them and into the cracks between them. It also blows dust away from the perimeter of the pile, excavating pits for the rocks to roll into – moving them away from their neighbours. Using computer models and wind tunnel tests, the researchers found that this motion spreads rocks out more evenly, so those that otherwise would be right next to each other wind up a few diameters apart. Journal reference: Geology (vol 37, p 55) More on these topics: