A new study reveals Pluto's dune systems contain wind-blown grains of frozen methane with possible remnants of nitrogen ice.
NASA’s New Horizons mission, which flew by the dwarf planet in July 2015, found that Pluto has towering mountains, but of water ice rather than rock; vast plains of frozen nitrogen and other exotic materials; and blue skies provided by a wispy atmosphere that contains no appreciable oxygen.
New studies reveal another foreign parallel, in which Pluto has an extensive dune system. However, the grains that make up the wind-blown mounds are certainly not sand.
The new discovery “shows us that Pluto’s atmosphere and surface are interacting in a way that geologically/geomorphologically alters the surface,” said study lead author Matt Telfer, a lecturer in physical geography at the University of Plymouth in England.
“That’s exciting not just because it shows (again) the dynamism of these small, cold, dark distant worlds, but also for its inferences for very early solar system bodies,” Telfer says in a Space.com report.
Telfer and his colleagues analyzed the imagery New Horizons captured during its epic flyby. They noticed a complex of ridges within Sputnik Planitia, a 620-mile-wide (1,000 kilometers) nitrogen-ice plain that forms the left lobe of Pluto’s famous “heart.”
The ridges ripple in a 47-mile-wide (75 km) sliver on the western edge of Sputnik Planitia, where the plain runs into the 3-mile-high (5 km) Al-Idrisi Montes mountain range. The newly identified features look a lot like wind-sculpted dunes, and that’s exactly what they are, according to the study team.
“Sublimation pits” are spots where sunlight has caused relatively large amounts of icy material to sublime, or transition directly from the solid phase to gas. New Horizons imagery has revealed thousands of such depressions across Sputnik Planitia, and a series of aligned pits was the most viable alternative explanation for the dune features, Telfer, and his colleagues wrote in the new study.
Sublimation is an important part of the dunes’ story, the researchers found. They performed modeling work that suggested Pluto’s winds are strong enough to create the Sputnik Planitia dune system, as long as the grains being blown were already airborne.
“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.
Telfer expressed similar sentiments: “It was hard to see how the wind could influence anything until you do the math.”
“The new study is far from the final word on Pluto’s dunes,” stressed Hayes, who also directs Cornell’s Spacecraft Planetary Imaging Facility.