Clearly, they are not of sand, as are the dunes of the Sahara, or even of water ice, as they are in Antarctica.
For some time, scientists have been intrigued by odd, regularly spaced ridges, that stuck out of Pluto's cold, dark plains like thumbprints pressed into ice.
The dwarf planet at the edge of our solar system is now thought to have winds and dunes on its surface, and there's a new theory that it was made from the collision of a billion comets. "However, despite being 30 times farther away from the Sun as the Earth, it turns out Pluto still has Earth-like characteristics".
The paper's lead author is Dr Matt Telfer, a physical geographer at the University of Plymouth. It looks nearly like a colder version of Earth in places. Now, Pluto, a place few expected could harbor such formations, joins the list of dune-bearing worlds.
The western margin of Sputnik Planitia. Pluto's Sputnik Planitia is capped with nitrogen ice, which the scientists estimated would not be sturdy enough to form dunes.
This was a surprising observation. The atmosphere, composed mainly of nitrogen with hints of methane and carbon monoxide, is 100,000 times thinner than Earth's.
After an epic trek through the Solar System that took almost a decade, New Horizons sped by at a speed of 58,536 km/h (36,373 mph), gathering data as it passed. Pluto has a system of dunes, but they're not made from sand.
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Combining an analysis of wind streak and dune-like features with spectral and numerical modeling, the scientists determined what might be the underlying architect of dunes on Pluto.
Once airborne, the particles are pushed by winds that blow between 18 and 24 miles an hour.
They discovered that was possible if there was sublimation at the surface, when a solid is turned directly into a gas. The upward force is what drives the piles of particles at the surface. Think of sand dunes on Earth: they are hills of sand built and shaped by wind. 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].
"On Earth, you need a certain strength of wind to maintain transport", said co-author Eric Parteli.
At the moment, the team also want to find out more about the dunes.
Though New Horizons is now too far from Pluto to gather any more useful information about the dwarf planet, its mission is still far from complete.
With that warming of the ice below the surface, methane crystals should enable nitrogen ice to sublimate - and that would allow the methane crystals to be wafted into the atmosphere.
According to the scientists, the undisturbed morphology of the dunes and their relationship with the underlying glacial ice suggested the features were likely to have been formed within the last 500,000 years, and possibly much more recently.