For years, two ice peaks on Pluto’s surface have inspired curiosity and bafflement among scientists in equal measure. Think “these giant broad mounds, and then this hummocky-like, undulating texture superimposed on top; and even on top of that there’s a smaller bouldery kind of texture,” as Kelsie Singer, a deputy project scientist at Southwest Research Institute in Boulder, Colorado, describes.
Like Singer, scientists have struggled to identify the nature of these marauding twin peaks. Some hypothesized it may be the fabled “ice volcanoes” — mounds gushing with ice slush instead of hot lava. There was little evidence to affirm this speculation thus far — until now.
“We found a field of very large icy volcanoes that look nothing like anything else we have seen in the solar system,” said Singer, who was the senior author of the paper. The discovery, published in Nature Communicationson Tuesday, uses a large set of topographical data and analyzes images gathered by NASA’s New Horizons mission. Ever since 2015, the spacecraft has lingered around Pluto and its moons — to piece together insights about the lone planet and recast much of what we know.
A view of Pluto’s bouldery surface shows not one, but a merger of multiple ice volcanoes on its landscape. For visual reference, some stretch up to 7,000 meters in height and spill out as far as 10-150km wide.
To put the confirmed discovery in perspective: icy volcanoes are not your run-of-the-mill ruptures in Earth’s crust. “It’s considered kind of a big claim to have icy volcanism,” Singer said. “It’s theoretically possible, but there aren’t a tonne of other examples in the solar system, and they are all really different looking, and do not look like the features on Pluto.” Unlike Mount Fuji or the famous Hawaiian volcanoes — which are big and smooth — Pluto’s is rife with icy texture. Think of it as the inverse of a typical volcano.
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That Pluto has volcanoes atop its surface is one thing. Another is the question of the nature of the material spewing out of these peaks. The data suggests the water ice carries a sort of “antifreeze” component within it — such as methanol. According to Singer, “it is still difficult to think that it would be liquid, because it’s just too cold – the average surface temperature on Pluto is about 40 Kelvin (-233 C),” adding that “it’s probably more, either slushy material, or it could even be mostly solid state – like a glacier is solid, but it can still flow.” She describes the material as “more like toothpaste while it flowed out of a volcanic vent onto the surface of Pluto.”
But given the temperature, the water shouldn’t flow at all. If we take this to its logical extent, Pluto’s core may be warmer than we realize; a planet needs interior heating to spur on a volcano. “This means Pluto has more internal heat than we thought it would, which means we don’t fully understand how planetary bodies work,” Singer conceded.
One intriguing takeaway that dangles in front of the community could be the promise of an ocean — and consequently, perhaps life — on the dwarf planet. The discovery of icy volcanoes and cryovolcanic activity may suggest Pluto’s subsurface ocean (which it once had) could still be present and that flowing liquid water could be close to the surface.
Arguably, there is still so much scientists don’t know about how reactive Pluto is, or why its subsurface may have active icy volcanoes. But the discovery indubitably raises interesting questions about Pluto’s dormancy. Lying among the icy recesses of the solar system, the dwarf planet was thought to be cold, inert, and largely lifeless; it is an “inert ball of ice” as some have coarsely claimed. That there is something sustaining the process of a volcano eruption on Pluto right now reignites a mystery — of life and survival.
