Wind-blown dunes are known on Earth, Mars, Venus, Saturn’s moon Titan, and Comet 67P/Churyumov-Gerasimenko — and, now on Pluto, according to a team of planetary researchers led by a University of Plymouth scientist.
This Pluto mosaic was made from New Horizons LORRI images taken on July 14, 2015, from a distance of 49,700 miles (80,000 km). 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. Image credit: S.A. Stern et al.
The researchers analyzed detailed images of one of Pluto’s largest features, a vast ice plain called Sputnik Planitia, captured in July 2015 by NASA’s New Horizons spacecraft.
Those images showed that on the boundary of the region, and pushed up against a major mountain range, there is a series of dunes spread across an area less than 47 miles (75 km) across.
Pluto’s dunes are unlike the dunes made of sand seen on Earth though; instead, they are likely made of tiny grains of methane ice.
Modeling by the team shows that Pluto’s moderate winds (which can reach between 19 and 25 mph, or 30-40 kmh) can create these dunes once the grains are airborne.
However, a process called sublimation is required first, to lift the grains from the planet’s surface. In this process, the Sun heats surface ice enough that gas is released into the atmosphere, lofting particles into the air as a result.
The likely source of the dune grains is methane ice blown from nearby mountains, although nitrogen ice cannot be ruled out, as a source.
The scientists also believe the undisturbed morphology of the dunes and their relationship with the underlying glacial ice suggests the features are likely to have been formed within the last 500,000 years, and possibly much more recently.
This image taken during NASA’s 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. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute.
“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 Dr. Matt Telfer, from the School of Geography, Earth and Environmental Science at the University of Plymouth.
“It turns out that even though there is so little atmosphere, and the surface temperature is around minus 382 degrees Fahrenheit (minus 230 degrees Celsius), we still get dunes forming.”
“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 non-cohesive surface and wind you need for dunes.”
“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.”
“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,” said co-author Dr. Eric Parteli, from the Department of Geosciences at the University of Cologne.
“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.”
“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,” said co-author Dr. Jani Radebaugh, from the Department of Geological Sciences, College of Physical and Mathematical Sciences at Brigham Young University.
“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 findings appear in the journal Science.
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Matt W. Telfer et al. Dunes on Pluto. Science 360 (6392): 992-997; doi: 10.1126/science.aao2975
