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The laws of attraction rule Titan’s sands. Static electricity clumping up sand could explain the strange dunes on Saturn’s largest moon.

Titan is a hazy moon with a thick, orange nitrogen atmosphere. Its poles are home to placid methane lakes, and its equatorial regions are covered with dunes up to 100 metres high.

The dunes seem to be facing in the wrong direction, though. The prevailing winds on Titan blow toward the west, but the dunes point east. “You’ve got this apparent paradox,” says at the Georgia Institute of Technology in Atlanta. “The winds are moving one way and the sediments are moving the other way.”

To understand the shifting of Titan’s sands, Dufek and his colleagues placed grains of organic materials like those on Titan’s surface in a chamber with conditions simulating Titan’s and spun them in a cylindrical tumbler.

Packing peanuts

When they opened the chamber, static electricity from the grains jostling in the dry air had clumped them together. “It was like when you open a box on a winter morning and the packing peanuts stick everywhere,” says Dufek. “These hydrocarbons on Titan are low density and they stick to everything, just like packing peanuts do.”

Grains on Titan can maintain that charge and stick together for much longer than particles on Earth could, because of their low density and the dryness of Titan’s atmosphere.

That could explain why the dunes don’t align with the wind. The breeze close to Titan’s surface is relatively mild, generally staying below 5 kilometres per hour. The sand’s “stickiness” would make it difficult for such low winds to move them.

More powerful winds from storms or seasonal changes could blow otherwise-stable sands eastward, forming the dunes that we see today.

“The relative importance of electrostatic forces on blowing sand are likely to be more significant on Titan,” says at the Johns Hopkins University Applied Physics Lab in Laurel, Maryland. “The wind speed at which particles start to move could be higher than we might otherwise expect.”

Electric snow

The unique clumping of Titan’s sands may even explain how the grains got there in the first place. Their make-up is similar to particles suspended in the soupy atmosphere, but the sand grains are much bigger.

“The atmospheric particles are very small, so they can’t be the things blowing around in those dunes, but this is one way that we could make them grow,” says at Brigham Young University in Utah.

Once enough particles had clumped together, they would fall out of the sky, coating the moon’s surface like electric snow.