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‘Surprising’ dunes of methane ice found on Pluto

02 June 2018

Launched in 2006, New Horizons was the first spacecraft ever to visit Pluto, passing within 12,500 kilometres.

This led them to conclude that the particles are most likely the result of sublimation, where solid nitrogen is converted into gas and releases sand-sized grains of methane in the process. This view is projected from a point 1,118 miles (1,800 km) above Pluto's equator, looking northeast over the dark, cratered Cthulhu Regio toward the bright, smooth expanse of icy plains called Sputnik Planitia. 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. The ice is a mixture of nitrogen, carbon monoxide and methane; according to the model, methane is still solid as nitrogen vaporises, and so grains of methane ice are thrown from the surface to be caught by the wind. Sastrugi - parallel wave-like ridges caused by winds on a hard snow surface; barchan - crescent mounds that tend to be wider than they are long; and seif - linear dunes with two slip faces, are just three of the very different types of dune that are found on Earth. "It turns out that even though there is so little atmosphere, and the surface temperature is around -230 degrees Celsius [-382 degrees Fahrenheit], we still get dunes forming".

He noted there are dunes on the scorching surface of Venus under a dense atmosphere and out in the distant reaches of the solar system at minus 230C under a thin atmosphere.

The dunes are something else that Pluto would have in common with comet 67/P, which stunned scientists with its combination of rippled dusty flanks and sharp-edged cliffs.

On Earth, we have a rich variety of dunes dependent on the composition and size of the grains and the strength and direction of the wind.

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Modeling by the team shows that Pluto's moderate winds (which can reach between 19 and 25 miles per hour, or 30-40 kmh) can create these dunes once the grains are airborne.

The paper's lead author is Dr Matt Telfer, a physical geographer at the University of Plymouth. Jani Radebaughis, the co-author of the study and an associate professor of the geological sciences department at the Brigham Young University.

The dunes have reportedly formed in the last 500,000 years.

By Earth's standards, you could hardly imagine a stranger world than frigid, tiny Pluto. "Accordingly, much work is left to do to understand dunes on Pluto".

"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", he said. "Put together, we have found that these combined processes can form dunes under normal, everyday wind conditions on Pluto", said Dr Eric Parteli, Lecturer in Computational Geosciences at the University of Cologne. If this is true, the dunes have to be more recent than the action of this convection otherwise they'd be churned apart by it. At the moment the space probe New Horizons is approaching another object in the Kuiper belt TRANS-Neptunian asteroid 2014 MU69.

‘Surprising’ dunes of methane ice found on Pluto