Scientists have detected a large field of dunes on the surface of the distant, frigid dwarf planet Pluto apparently composed of windswept, sand-sized grains of frozen methane.
The dunes, spotted on images taken by Nasa’s New Horizons spacecraft during its 2015 flyby, sit at the boundary between a heart-shaped nitrogen glacier about the size of France called Sputnik Planitia and the Al Idrisi Montes mountain range made of frozen water, scientists said on Thursday.
Jani Radebaugh, a planetary scientist at Brigham Young University, said: “Pluto, even though it’s so far away from Earth and so very cold, has a riot of processes we never expected to see. It is far more interesting than any of us dreamed, and tells us that these very distant bodies are well worth visiting.”
The existence of the dunes, which cover about 775 sq miles (2,000 sq km), came as a surprise. There was some doubt about whether Pluto’s extremely thin atmosphere, mainly nitrogen with minor amounts of methane and carbon monoxide, could muster the wind needed to form such features.
Pluto, smaller than Earth’s moon with a diameter of about 1,400 miles (2,380 km), orbits about 3.6bn miles (5.8bn km) away from the sun, almost 40 times farther than Earth’s orbit, with a surface marked by plains, mountains, craters and valleys.
Methane, carbon monoxide, carbon dioxide and nitrogen, all gaseous on Earth, are rendered solid with Pluto’s temperatures near absolute zero. Pluto’s dunes were shaped by moderate winds reaching about 22 mph (35 kph) apparently blowing fine-grained frozen methane bits from mountaintops.
Pluto’s dunes resemble some on Earth like those in California’s Death Valley and China’s Taklamakan desert, though their composition differs, according to Radebaugh.
“It’s a little bit lower density than sand we’re used to holding on the Earth,” she said. “So it would feel lighter in your hand, but it would still be granular and would kind of flow off of your hand, and your feet would kind of crunch them as you’re walking along. It would just kind of feel a lot like you’re on another sand dune on the Earth.”
University of Cologne physicist and geoscientist Eric Parteli said dunes had been detected elsewhere in the solar system including on the planets Mars and Venus, Saturn’s moon Titan and Neptune’s moon Triton. Pluto’s dunes probably formed within the past 500,000 years and potentially more recently, Parteli added.
The University of Plymouth’s planetary scientist Matt Telfer, who estimates the dunes are tens of metres high, said: “Given we have dunes on the scorching surface of Venus under a dense atmosphere, and out in the distant reaches of the solar system at minus 230 degrees Celsius (minus 382 Fahrenheit) under a thin atmosphere, yes, dunes do have a habit of cropping up in a lot of surprising places.”
“Much work is left to do to understand dunes on Pluto,” Cornell University’s Alexander Hayes wrote in a companion article. He was not involved in the study. “Most notably, it remains to be shown how high the dunes are, when they are most active, whether they change” and whether particles can be swept into dunes without rising into the air.
The research was published in the journal Science.