Images of Pluto's surface have revealed the dwarf planet's hidden secret: a network of giant ice volcanoes. According to astronomers behind the discovery published this week in Nature Communications, the volcanoes appear to have erupted in an icy slush relatively recently.
"There was no other areas on Pluto that look like this region," says study author Kelsi Singer, a planetary scientist at the Southwest Research Institute, told Space’s Rebecca Sohn. "It's totally unique in the solar system."
The peaks were first spotted by NASA's New Horizons spacecraft, which snapped photos of the dwarf planet’s surface and its moons during a flyby in July 2015. New Horizon’s images allow astronomers to take a closer look at Pluto than ever before, which led them to pinpoint an area with two towering peaks suspected to be ice-filled volcanoes. Now, scientists say they’ve found evidence of erupted ice lava in the images, an indication that Pluto’s dramatic peaks are, in fact, a collection of icy volcanoes.
“We tried to find some other way to explain it, but we just really couldn’t,” Singer tells Robin George Andrews for the New York Times.
Instead of erupting with hot magma, ice volcanoes, called cryovolcanoes, ooze a mixture of water ice, along with substances like ammonia or methane. Scientists have been looking for evidence of such volcanoes in the coldest reaches of our solar system, including on the dwarf planet Ceres and Saturn's largest moon, Titan. Because Pluto rests on the frigid edge of our solar system in the Kuiper Belt, it has long been suspected to be home to cryovolcanoes. Pluto’s average temperature is a brisk minus 387 degrees Fahrenheit (minus 232 degrees Celsius), so any slushy eruptions would likely retain their shape on the dwarf planet’s surface.
"The icy material was probably more of a slushy mix of ice and water or more like toothpaste while it flowed out of a volcanic vent onto the surface of Pluto," Singer tells CNN’s Ashley Strickland. "It is so cold on the surface of Pluto that liquid water cannot remain there for long. In some cases, the flow of material formed the massive domes that we see, as well as the lumpy terrain found everywhere in this region."
The area around the volcanoes doesn't have the impact craters usually dotted across Pluto's surface, which suggests the colony of cryovolcanoes were active around 100 to 200 million years ago. Given the ice volcanoes’ relatively recent activity, it’s possible that they may erupt in the future.
"They could be like volcanoes on Earth that remain dormant for some time and then are active again," Singer says to CNN.
The dwarf planet once had a subsurface ocean, and evidence of recently-active cryovolcanoes suggests it may still be present, with Pluto’s network of ice volcanoes possibly feeding off one liquid source. The finding also means that there is more heat in Pluto's interior than astronomers previously thought, likely powered by the decay of radioactive elements in the dwarf planet's interior, per Linda Geddes for the Guardian. The possibility of a liquid ocean beneath Pluto’s surface increases the chance of life existing on the dwarf planet from none, to slim.