Monday, 20 August, 2018

Pluto Methane Dunes Made of Tiny Frozen Grains of Gas

Dunes on Pluto's surface. Image credit NASA  Johns Hopkins University Applied Physics Laboratory  Southwest Research Institute Dunes on Pluto's surface. Image credit NASA Johns Hopkins University Applied Physics Laboratory Southwest Research Institute
Cary Marshall | 03 June, 2018, 03:37

BYU Professor Jani Radebaugh and a team of worldwide scientists discovered a series of "sand dunes" made of methane ice on Pluto.

Researchers modeled the conditions they saw and concluded that the "sand" is made of nitrogen or methane ice.

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. Scientists were initially surprised to see the complex geology of Pluto, with ice mountains and vast frozen plains.

"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.

Pluto's icy surface is even more exotic than astronomers previously thought. But the dunes, he said, show that Pluto "is actually so similar".

Now, though, thanks to the spectacular images returned by the New Horizons spacecraft that flew past Pluto in 2015, we know that, far from being a dreary and undistinguished body, Pluto is a lively and active object that displays a fantastic variety of landscapes.

A study published today in the journal Science confirms that the icy dwarf planet has dunes of its own.

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"We have been focusing on what's close to us", said Radebaugh, "but there's a wealth of information in the distant reaches of the solar system too".

"We knew that every solar system body with an atmosphere and a solid rocky surface has dunes on it, but we didn't know what we'd find on Pluto", Matt Telfer, lecturer in physical geography at the University of Plymouth and the paper's lead author.

Dunes have already been found on Mars, Venus, Saturn's moon, Titan and even a comet. New analysis of images collected by the space probe of the dwarf planet's surface has confirmed the presence of dunes. The driving force of this process may be the heating of the atmosphere by the Sun, which raises the temperature above minus 230 degrees Celsius, that is the freezing point of nitrogen.

'It's a little bit lower density than sand we're used to holding on the Earth, ' explained co-author Jani Radebaugh from Brigham Young University. The grains of methane are then lifted by this gas into the thin atmosphere of the Pluto. Pluto's mild winds then carried the particles to the area where the dunes on Pluto are now located.

Pluto isn't the only place in our solar system with dunes or ice or sand.

Dr Eric Parteli, Lecturer in Computational Geosciences at the University of Cologne, said: "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".

THIS highest-resolution file image from Nasa's New Horizons spacecraft shows great blocks of Pluto's water-ice crust appearing jammed together. It's expected to zip past the Kuiper Belt object nicknamed Ultima Thule - orbiting 1 billion miles (1.6 billion kilometers) beyond Pluto - on January 1.

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