Wind and a process called sublimation helped sculpt the ripples, a new study suggests
SWRI, JHU Applied Physics Lab, NASA
Pluto’s heart-shaped plains are striped with sand dunes, where the sand is made of solid methane ice, a new study finds.
Images from the New Horizons spacecraft’s July 2015 flyby of Pluto show 357 linear ridges that planetary scientist Matt Telfer of the University of Plymouth in England and colleagues interpret as dunes that have been shaped by a novel process, the team reports in the June 1 Science.
The ripples lie parallel to the Al-Idrisi Montes mountain range at the western edge of Sputnik Planitia, the wide plains of nitrogen and methane ice that form part of Pluto’s famous heart-shaped region. Relatively strong winds, between about 1 and 10 meters per second, should blow from those mountains across the plains.
Computer simulations suggest that despite Pluto’s thin atmosphere, these winds are strong enough to keep sand-sized methane ice particles moving once they become airborne. But the winds are probably too weak to lift the grains off the ground in the first place.
Instead, little puffs of air coming from Sputnik Planitia’s nitrogen ice as the sun heats it could boost the methane ice particles skyward and into the wind, the team suggests. That process by which solids turn directly into vapor is called sublimation.
Streaks that look like dunes (yellow arrow) were found in the northwest of a vast plain called Sputnik Planitia, and run parallel to the Al-Idrisi Montes mountain range. Winds blow across the range and help sculpt the features, which are made of solid methane ice, a new study proposes.
“That’s a novel, interesting idea,” says planetary scientist Alexander Hayes of Cornell University who was not involved in the work, but wrote a commentary piece in the same issue of Science. But the notion raises a reason for caution: Sublimation alone could explain some of the features, without the need for wind, he says.
Dunes are found across the solar system, from Earth (SN: 12/26/15, p. 5) to Mars (SN Online: 2/10/10) to Saturn’s moon Titan (SN Online: 8/28/13). Each of these worlds has the ingredients for dunes: a supply of loose, grainy material and an atmosphere or fluid to carry grains around.
“When you look at dunes across the solar system, something that always strikes me is that they form the same patterns, regardless of the environment,” Hayes says. Finding dunes on Pluto, too, suggests that the features may be ubiquitous. “If you have the material and a way to move it, you form dunes. That’s what this is telling us.”
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