Something weird is at work on the cold, dark plains of Pluto, where hundreds of regularly spaced ridges look a bit like an alien thumbprint pressed into extraterrestrial ice. Today, though, researchers report in the journal Science that the strange landscape is actually a dune field crafted from methane “sand.”

The observation is startling, given that scientists thought Pluto’s tenuous atmosphere wasn’t necessarily robust enough to support the formation of dunes, which by most definitions are sculpted by wind.

“Dunes on Pluto, or any other body, tell us there is a significant enough atmosphere to move materials around, and that there are particles to move—in this case, frozen methane sand,” says study coauthor Jani Radebaugh of Brigham Young