Wondrous dunes on Pluto are made of grains of frozen methane

Katie Ramirez
June 2, 2018

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.

"When we first saw the images of New Horizons, we immediately thought they were dunes, which was very surprising because we knew there was not really any atmosphere", says Jani Radebaugh, co-discoverer and geology professor at Brigham Young University in the United States.

"It is another piece of the jigsaw in making sense of this diverse and remote body, and gives us a more fundamental understanding of the geological processes which are influencing it". These closely spaced ice thin ice blades are also found on Earth and are caused by the sublimation of snow in dry air at high altitudes.

"These are not just balls of ice far out in space", he said, adding that frozen worlds on the fringes of our solar system, like the dwarf planet Pluto, might have been active early on.

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.

Where Sputnik Planitia approaches mountains of ice, its surface ripples.

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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.

The images showed that on the boundary of the Sputnik Planitia ice plain, pushed up against a major mountain range, there is a series of dunes spreading across an area less than 46.6 miles.

Until the New Horizons spacecraft flew past it in 2015, humanity had very little knowledge about this body, and many were expecting a rather tiresome, icy asteroid. "It would just kind of feel a lot like you're on another sand dune on the Earth". With its dunes, Pluto joins a club that includes Earth, Mars, Venus, Saturn's moon Titan and, possibly, a comet. However despite being 30 times further away from the sun as the Earth, it turns out Pluto still has Earth-like characteristics. 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.

But with the surface frozen, the researchers wondered what it could be made of.

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 ideal location for such regular surface formations to appear. In comparison with the pressure of Earth's atmosphere, the Pluto's atmosphere has got a lower surface pressure. "Accordingly, much work is left to do to understand dunes on Pluto". Comparative planetary morphology will be the key that helps us decipher how these planets have formed and evolved. 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. "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.

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