Ice volcanoes on Pluto suggest dwarf planet may not be so cold after all

Pluto, once considered the ninth planet in our solar system until it was demoted to a dwarf planet in 2006, had been shrouded in mystery since its discovery in 1930. But thanks to NASA's ambitious New Horizons flyby in 2015, the curtain has been pulled back, and astronomers continue to reveal that Pluto is much more interesting than previously thought. 

When New Horizons flew 7,800 kilometres above the surface of Pluto, it revealed a world unlike anything we'd ever seen. There were flat plains, mountains and even a thin atmosphere. It was far from the stagnant, blue, icy world that had been depicted in artists' impressions over the decades. It was an eye-opening discovery.

And one of the most intriguing images sent back to Earth was one that suggested the possibility of ice volcanoes, also called cryovolcanoes.

"[At the time], we got back little chunks of images, either smaller images or parts of images first, because we couldn't get all the data back at once. And it just so happens that one of those postage stamps that we got back did happen to have part of this cyrovolcanic region in it," said Kelsi Singer, a planetary scientist at the Southwest Research Institute in Boulder, Colo., and deputy project scientist on New Horizons.

These volcanoes wouldn't be something like those here on Earth. Instead, they would be fed by water ice and other volatiles like nitrogen, methane and carbon monoxide. 

Still, there was some debate that the images were being interpreted properly.

Now, a new study published Tuesday in the journal Nature Communications provides more evidence to support that the icy world is home to these strange cryovolcanoes, some seven kilometres tall and roughly 10-to-150 kilometres wide.

"Now we have all the data back. And so we can use all of those pieces of information together," Singer, lead author of the study, said. "And that includes not just the images, but also topography that's created from the images, because sometimes your eye can trick you. So the topography makes you be honest about what the features are." 

Though these cool volcanoes aren't quite like the ones we see here on Earth, they do have some similarities. 

Instead of a violent eruption with lava, rock and dust spewing into the sky, it's believed that the material these volcanoes produce — likely some water ice, though there is also nitrogen, methane and carbon monoxide ice on Pluto — are brought to the surface slowly by some sort of internal heating mechanism.

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But there's something that remains to be explained in their findings.

"Between the composition data and the way the features are, we've said that it has to be at least a good part water ice," Singer said of the features seen on Pluto. "And that's difficult to explain, because you still have to have that stuff be mobile, and it essentially requires some kind of heat source."

There are a couple of ways to get that heat source. One is from the rocky core of a moon or planet where elements break down. That heat can remain trapped until it is released in some way.