Dunes of methane ice found on Pluto’s cold surface, new study shows

Pluto is an oddball. 

The dwarf planet plays host to mountains made of ice that could rival the Rockies alongside a heart-shaped plain of ice that looks like the world’s dominant feature when seen from high above. 

But that’s not all. 

According to a new study in the journal Science this week that makes use of images taken during the New Horizons flyby of Pluto in July 2015, the tiny world also has dunes of methane ice at the border of part of the heart-shaped region known as Sputnik Planitia.

“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,” study co-author Jani Radebaugh said in a statement

“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.”

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The study’s authors think that Pluto’s winds have deposited sand grain-sized crystals of methane between the mountains bordering Sputnik Planitia and the plains itself, creating these dunes. 

The study suggests that those grains of methane are produced through a process known as sublimation, where solid nitrogen actually converts directly into a gas, skipping the liquid phase. This effectively transports those small grains of methane into Pluto’s atmosphere, where they are blown around by winds before eventually settling into the dunes.

“It turns out that even though there is so little atmosphere, and the surface temperature is around minus-230 degrees Celsius, we still get dunes forming,” lead author of the study Matt Telfer said in the statement. 

“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.”

That said, it’s not a sure thing that these grains are made through sublimation. There might be some other mysterious process at work. 

It’s possible that Pluto’s climate was different in the past, leading to another means of kicking off this kind of methane crystal production, according to William McKinnon, a Pluto researcher who had no part in the new study.

“Maybe atmospheric pressure on Pluto in recent geologic past was higher,” McKinnon said in an interview, meaning that the dunes could have formed through some other geological process that didn’t involve sublimation of nitrogen in the past.

Pluto isn’t the only place in our solar system with dunes or ice or sand. 

Earth, obviously, has dunes of sand all across its surface, and Saturn’s huge moon Titan plays host to dunes of methane and ethane on its icy surface as well. 

“Despite vast differences in gravity, atmospheric pressure, and sediment type, windblown sand dunes on Earth, Mars, Venus, and Titan self-organize into remarkably similar landscape patterns,” Alexander Hayes wrote in a commentary on the new study. 

The next phase for this research might actually involve looking to places other than Pluto out there in the solar system, according to McKinnon. 

In order to figure out how exactly these dunes formed, it makes sense to hunt for analogs elsewhere as well. 

“I would look for dunes in the next thinnest atmosphere we can find,” McKinnon said. “[The] tops of the Martian volcanoes are a good place to start.”