"Racetrack Playa" sounds like the screenname of an online teenager you're competing against in Need for Speed, but scientists recognize it as the name of a dried-up lake in Death Valley. For a century, scientific minds have been puzzled by a well-documented, poorly-understood phenomenon occuring at Racetrack Playa: Enormous stones, some up to 700 pounds, appear to have somehow moved themselves across the lakebed floor in random patterns, leaving a furrowed trail behind them.
No one had ever seen these "sailing stones" move, but many photographed the end result. The original thought was that the lakebed forms a thin sheet of ice on it, and that the wind then blows the rocks across it; but that theory was discounted after researchers calculated it would take wind speeds of hundreds of miles per hour to move the rocks, while the wind at the Racetrack maxes out around 90 m.p.h. And if you're wondering why they don't just strap a GoPro camera onto a rock to see what's going on, scientists returning to the site over the years have calculated that the rocks move for short periods of time, just once every three years. That's a bit longer than your battery's likely to last.
However, a fortunate collision between two of these magic rocks provided planetary scientist Ralph Lorenz with an interesting discovery:
Lorenz, studying the trails left by the stones, observed that one rock had collided against another and been deflected. "There was a rock trail and it looked like it hit another rock and bounced, but the trail didn't go all the way up to other the rock, like it was repelled somehow," Lorenz told Smithsonian Magazine. In other words, there was some kind of force-field-like barrier around each rock that prevented total contact.
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Via Chuck Sherwood, Senior Associate, TeleDimensions, Inc