Pluto has dunes, but they are not made of sand

This picture was taken by NASA’s New Horizons spacecraft during its July 2015 flyby of Pluto gives the mountain range, on the edge of the dwarf planet Sputnik Planitia ice plain. Dune formations are clearly visible in the lower half of the image.

(NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

Pluto is an eerie valley of the world, with landscapes and vistas that seem strikingly similar to that of the Earth, until you take a closer look.

NASA’s New Horizons mission, which flew by the dwarf planet in July 2015, found that Pluto has high mountains, but of water-ice rather than rock; vast plains of frozen nitrogen and other exotic materials; and blue skies by a thin atmosphere contains no appreciable oxygen.

And now, a new study reveals another alien parallel: Pluto has an extensive dune system, but the grains from which the wind-blown mounds are certainly not sand. [Destination Pluto: NASA’s New Horizons Mission in Pictures]

The new discovery “shows us that Pluto’s atmosphere and surface interact in a way that geological/geomorphological changes to the surface,” said study lead author Matt, a lecturer in physical geography at the University of Plymouth in England.

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“That is exciting, not only because it shows (again) to the dynamics of this small, dark, cold, distant worlds, but also for the conclusions for very early in the solar system,” told His via e-mail.

Where the mountains meet the plains

His and his colleagues analysed the images New Horizons captured during his epic flyby. She saw a complex of ridges in the Sputnik Planitia, a 620-km-wide (1000 km) of nitrogen ice plain is the left lobe of Pluto’s famous “heart”.

The ridges of the ripple in a 47-mile-wide (75 km) strip on the western edge of the Sputnik Planitia, where the plain runs in the 3-mile-high (5 km) Al-Idrisi Montes mountains. The newly identified features that are similar to the wind formed dunes, and that is exactly what they are, according to the study team.

“We are sure,” he said. “It’s actually a relatively simple things, such as their location, alignment (undisturbed by glacial movement, in contrast to the sublimation pits elsewhere), orientation (including the adjacent orthogonal wind streaks), and changes in the regional orientation and distance that nail. It makes perfect sense for dunes, and does not match what we would see for sublimation pits.”

“Sublimation pits” spots where the sunlight has caused relatively large quantities of icy material, or transition directly from the solid phase to gas. New Horizons images have revealed thousands of such depressions on the Sputnik Planitia, and a series of aligned pits was the most viable alternative explanation for the dune features His-and his colleagues wrote in the new study, which was published today (31 May) in the journal Science.

Sublimation is an important part of the dunes’ story, the researchers found. They did the modeling work that suggested Pluto, the wind is strong enough to Sputnik Planitia dune system as long as the grain is blown were already in the air. Sublimation is virtually the only way to make this possible, the grains are lofted by rising gas, according to the study team.

The wind-blown grains are probably frozen methane, which is sourced from the nearby mountain range, but a bit of nitrogen ice are another possibility, the authors wrote.

The lack of craters spots Sputnik Planitia shows that the ice is solid, the surface is formed by geological activity recently. And the dunes are likely to be young; the research team believes they formed in the past 500,000 years or so. [Pluto’s Heart: A Cosmic Valentine in Photos]

A surprising discovery

Dune systems seem to be common throughout the solar system. Such features are confirmed on the Earth, Mars, Venus, and Saturn’s huge moon Titan, for example, and they may even exist on Comet 67P/Churyumov-Gerasimenko, which was examined closely by the european Rosetta mission from 2014 to 2016.

Still, the find of the dunes on Pluto was unexpected, in view of the dwarf planet, the very thin air, experts said.

“What makes this discovery surprising is that the sediment may be mobilized despite Pluto’s thin 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.

Expressed similar feelings: “It was difficult to see how the wind can influence everything, until you get to the math.”

The new study is far from the last word on Pluto dunes, stressed Hayes, who also directs Cornell’s Spacecraft Planetary Imaging Facility.

“Nature has the tendency to converge in the direction of a set of relatively few forms, and general patterns using a variety of processes,” he wrote. “Consequently, a lot of work to do to understand the dunes on Pluto. In particular, it remains to be shown how high the dunes are, when they are most active, or they change, and whether entrainment can occur without lofting.”

New Horizons’ work is far from done, by the way. The probe is now ready for a flyby of a small object with the name 2014 MU69, which is located about 1 billion miles (1.6 billion km) beyond Pluto. That close encounter, which will take place on Jan. 1, 2019, is the centerpiece of the New Horizon an extended mission.

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