Despite the vast distances that separate them, Saturn's moon Titan and Earth have at least one thing in common: towering dunes shaped by wind. Radar images taken by the Cassini spacecraft as it passed by the frigid globe revealed distinctive linear features that almost precisely mimic sand dunes in our own planet's deserts.

"It's bizarre," says Ralph Lorenz of the University of Arizona, lead author of the study presenting the findings in today's Science. "These images from a moon of Saturn look just like radar images of Namibia or Arabia."

Saturn's gravity pulls Titan's methane and nitrogen atmosphere--just like the moon pulls Earth's oceans and atmosphere, only 400 times more powerfully--and creates winds averaging a mile per hour. In the Saturnian moon's dense shroud and low gravity this is enough to blow particles this way and that on the surface. As a result, dunes form in the same distinctive shape familiar on our own planet, where sand interacts with winds that blow in two different directions.

The material that forms Titan's dunes is exotic, however, either carved from ice by methane rain or formed by sunlight striking the volatile atmosphere and creating tiny aerosols that drift down to the surface--an alien sandstorm of hydrocarbons. "These grains might resemble coffee grounds," Lorenz speculates.

The dunes also grow larger on Titan than on Earth, with some reaching a height equivalent to that of a 33-story building. And the dune fields cover vast stretches of the satellite's equatorial region; one field alone runs more than 930 miles, Lorenz says. Still, the same physical processes familiar from our home planet appear to be at work even in this alien context.