Strange streaks. Martian storms leave tracks like these. Edgett declined to release the photo of a dust devil in action, shown to the audience, until his data are published.

Martian Tire Tracks Explained

WASHINGTON, D.C.--Researchers have discovered what causes the dark, mostly straight streaks that adorn the plains of Mars. "We caught a dust devil in action," whipped up by the fierce martian winds, said geologist Ken Edgett of Malin Space Science Systems in San Diego. He unveiled the image here Friday at the annual meeting of the American Association for the Advancement of Science, which publishes ScienceNOW.

So far, there were few hints as to the origin of the Martian stripes. Edgett dubbed them "SUV tracks," because they resemble the scars left by earthly sports utility vehicles. Now, after studying pictures recently beamed from NASA's Mars Global Surveyor spacecraft, he believes a blurry circle at the leading edge of one streak is one of the well-known martian dust devils in action. The minitornadoes kick up dust on the plains, he explains, exposing a darker material underneath that is visible as a streak. The picture even shows wisps, apparently of dust, "being sucked into the column," he says. "It's pretty neat."