The Secret to Pluto’s Dunes? Methane Ice “Sand” and a Gentle Wind

This image taken during the New Horizons mission shows the mountain range on the edge of the Sputnik Planitia ice plain, with dune formations clearly visible in the bottom half of the picture. (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

(CN) – New images of Pluto’s surface reveal dunes that scientists say are likely to have been formed of methane ice grains released into its low-pressure atmosphere.

In a study published Thursday in the journal Science, an international team of planetary scientists, geographers and physicists presents its analysis of detailed images of the dwarf planet’s surface captured by NASA’s New Horizons spacecraft in July 2015.

The images show that on the boundary of Pluto’s Sputnik Planitia ice plain, and nestled against a major mountain range, there is a series of dunes spanning an area no larger than 46.6 miles across.

“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,” said lead author Matt Telfer, a lecturer in physical geography at the University of Plymouth in the United Kingdom. “It turns out that even though there is so little atmosphere, and the surface temperature is around -382 degrees Fahrenheit, we still get dunes forming.”

After performing spatial analysis of the dunes and spectral and numerical modeling, the team believes sublimation – which transforms solid nitrogen directly into a gas – results in the release of sand-sized grains of methane into the environment.

These grains are then transported by Pluto’s moderate winds, which can reach between 18.6 and 24.9 miles per hour, with the border of the mountain range and ice plain offering the ideal location for such regular surface formations to appear.

“On Earth, you need a certain strength of wind to release sand particles into the air, but winds that are 20 percent weaker are then sufficient to maintain transport,” said co-author Eric Parteli, a lecturer in computational geosciences at the University of Cologne in Germany. “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. The temperature gradients in the granular ice layer, caused by solar radiation, also play an important role in the onset of the saltation process.

“Put together, we have found that these combined processes can form dunes under normal, everyday wind conditions on Pluto.”

The researchers believe the undisturbed morphology of the dunes and their connection with the underlying glacial ice mean they’re likely to have been formed within the past 500,000 years, and potentially much more recently.

“The New Horizons data has given us a new level of detail, but we had to work hard to explain how it was possible to get the supply of sediment, a noncohesive surface and wind you need for dunes,” Telfer said. “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.”

(NASA/New Horizons)

Co-author Jani Radebaugh, an associate professor in the department of geological sciences at Brigham Young University, added that the findings both reveal features of Pluto that are similar to Earth and offer evidence of the value of studying planetary bodies beyond our immediate neighbors.

“When we first saw the New Horizons images, we thought instantly that these were dunes, but it was really surprising because we know there is not much of an atmosphere,” Radebaugh said. “However, despite being 30 times further away from the sun as the Earth, it turns out Pluto still has Earth-like characteristics.

“We have been focusing on what’s close to us, but there’s a wealth of information in the distant reaches of the solar system too.”

The researchers now plan to continue to investigate the history of Pluto’s dunes through computer simulations, which will allow them to examine the role wind has played in the dwarf planet’s wider geology.

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