NASA’s New Horizons probe flew past Pluto in July 2015 and found dunes. But, how can dunes form without wind? Well, they are not sand dunes.

Astronomers have recently discovered surprising evidence for methane Pluto dunes.

Pluto’s dunes appear truly Earthly. They’re situated parallel to the edges of the adjacent mountains and perpendicular to the direction of nearby wind streaks. But they are nothing like the ones on Earth. Dunes on Earth require both tiny grains and wind to shape them. On Pluto, the air is only 0.001 percent as thick as on Earth. That means it’s too thin to carve dunes on its own.

“When we first saw the New Horizons images, we thought instantly that these were dunes but it was really surprising because we know there is not much of an atmosphere,” Jani Radebaugh, study co-author and associate professor in geological sciences at Brigham Young University, said in a statement. “However despite being 30 times further away from the sun as the Earth, it turns out Pluto still has Earth-like characteristics. We have been focusing on what’s close to us, but there’s a wealth of information in the distant reaches of the solar system too.”

What’s going on with the dunes on Pluto?

In Pluto’s thin atmosphere, solid nitrogen sitting on mountain peaks can spontaneously evaporate. This evaporating nitrogen can launch small particles of methane into the air. Once that happens, the extremely light breeze on the planet could push the methane particles, each about the size of a human fat cell, into the ridges observed by the New Horizons team.

Pluto’s winds can reach 18 to 24 miles per hour, creating and sculpting dunes.

“On Earth, you need a certain strength of wind to release sand particles into the air, but winds that are 20% weaker are then sufficient to maintain transport,” Eric Parteli, study co-author and lecturer in computational geosciences at the University of Cologne, said in a statement.

“The considerably lower gravity of Pluto and the extremely low atmospheric pressure means the winds needed to maintain sediment transport can be a hundred times lower. The temperature gradients in the granular ice layer, caused by solar radiation, also play an important role in the onset of the saltation process [movement of particles over an uneven surface]. Put together, we have found that these combined processes can form dunes under normal, everyday wind conditions on Pluto.”

Researchers discovered the dunes through the combination of an analysis of the famous map of Pluto’s surface which New Horizons probe produced, and the use of another scientist’s modeling.

The researchers published their results in Science.

Research also shows that the dunes are probably only about 500,000 years old at most, and are likely considerably younger.

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