Pluto has dunes, but they’re not made of sand

Scientists surprised to find dunes on Pluto that are made of tiny grains of methane

Dunes on Pluto made of tiny frozen grains of methane

"What makes this discovery surprising is that the sediment can be mobilized despite Pluto's tenuous atmosphere, with a surface pressure (1 Pa) that is a factor of 100,000 times lower than that on Earth", Alexander Hayes, an assistant professor of astronomy at Cornell University who was not involved in the new study, wrote in an accompanying "Perspectives" piece in the same issue of Science.

They are lying close to a range of mountains of water ice 5km high. Previously it was assumed that Pluto's atmosphere is too sparse and does not possess the qualities that are inherent in the atmosphere of our planet - for example, can't form dunes and dunes. Thought to be relatively recent, the parallel rows of dunes are located in Pluto's heart-shaped region at the base of mountains as tall as the Alps and formed from giant blocks of ice with frosty methane snowcaps. Pluto's mild winds then carried the particles to the area where the dunes on Pluto are now located.

The paper's lead author is Dr Matt Telfer, a physical geographer at the University of Plymouth.

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. We've found them on Mars, Venus, and Saturn's moon Titan. So, it's fair to call these dunes, but what are they? Such winds are generated by the downward flow of gases from the tops of the surrounding mountains, as well as through the process of sublimation of methane ice, i.e. its transition from the solid to the gaseous state.

The researchers at SwRI in Texas aren't ruling out other theories for the formation of Pluto, which sits far out at the edge of the solar system in the Kuiper Belt.

These are then transported by Pluto's moderate winds (which can reach between 30 and 40 kmh), with the border of the ice plain and mountain range providing the flawless location for such regular surface formations to appear. This is only possible with sublimation resulting in sand-like particles that are most likely methane, but scientists say it could also be nitrogen ice.

"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", said co-author Dr. Eric Parteli, from the Department of Geosciences at the University of Cologne.

Telfer and his colleagues have calculated that the dunes may be on the surface of Pluto, where the winds blow the strongest winds on the planet, reaching speeds of 10 meters per second. The temperature gradients in the granular ice layer, caused by solar radiation, also play an important role in the onset of the saltation process.

The dunes were likely formed within the last 500,000 years and possibly much more recently. "It turns out that even though there is so little atmosphere, and the surface temperature is around minus 230 degrees Celsius we still get dunes forming". There was some doubt about whether Pluto's extremely thin atmosphere, mainly nitrogen with minor amounts of methane and carbon monoxide, could muster the wind needed to form such features. Using all of the information gathered by New Horizons reveals that Pluto is a geologically active world with an atmosphere, which may or may not have liquids on its surface.

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