A huge, bizarre crater on the surface of our cosmic neighbor Pluto may actually be an icy supervolcano lying dormant.
The Kiladze Crater, a 27-mile wide structure situated in Sputnik Planitia, a heart-shaped region on Pluto's surface, is thought to be a powerful cryovolcano, according to a new research paper on the pre-print server arXiv.
Cryovolcanoes are similar to the regular volcanoes found on Earth, but instead of spewing lava, they spurt out frozen water and other chemicals such as ammonia from within a celestial body. Cryovolcanos have been found on many of the moons of Jupiter, Saturn, Uranus and Neptune, and on several comets passing through the solar system.
The arXiv, which is yet to be formally peer-reviewed, suggests that the Kiladze crater is actually a cryovolcano due to observations of its appearance made by the New Horizons probe during its Pluto flyby in 2015.
New Horizon's images of the dwarf planet revealed that there was water ice scattered around Kiladze, which was unusual as the rest of the planet is mostly covered in frozen methane and nitrogen ice. Additionally, spectroscopy of the crater revealed that the water ice contained ammonia.
"The tip-off that Kiladze is different from nearly all of the rest of the half of
Pluto's surface we explored with New Horizons in 2015, is the strong spectral
signature of water ice. The water ice stands out clearly from the methane
ice that covers much of the planet's surface," Dale Cruikshank, a NASA Ames Research Center planetary scientist and co-author of the paper, told Newsweek.
Kiladze's appearance also more closely resembles a tectonically formed crater, rather than an impact crater.
"While Kiladze bears some resemblance to an impact crater, it is somewhat
different in detail from other established impact craters on Pluto," Cruikshank said.
"Its shape (slightly elongated) and the absence of a substantial central peak are both distinguishing characteristics: the elongation is consistent with faulting (from tectonic forces over the entire area) and rows of collapse pits in the region. Much of the Kiladze rim is collapsed into subsidence pits, similar to the collapse pits populating the entire area."
If Kiladze is indeed a cryovolcano, it would be a fascinating find for scientists, as it would require heating from within the dwarf planet.
"There are various lines of evidence that the planet once had an internal ocean that was global in scale. As the planet cooled, it is plausible that pockets of liquid water were left behind, and perhaps our eruptions of water onto the surface tap into those pockets," Cruikshank said.
Pluto, which orbits the sun at an average distance of 3.7 billion miles, is intensely cold and small, with a diameter of only around two-thirds the size of Earth's moon. The presence of a cryovolcano on Pluto would give scientists clues as to what Pluto might be made of internally, as its innards are forced to the surface by forces within.
Pluto's bedrock is mostly water ice, with a thin layer of methane and nitrogen surface ice on top, coated by tholins, which are hydrocarbons created by the bombardment of cosmic rays and other radiation. Its core is made of rock that scientists think must contain radioactive elements, which produce the heat needed for cryovolcano formation via radioactive decay. If this is the case, there may be a layer of liquid water or icy slush between the icy crust and the rocky core.
"There are at least two other cryovolcanic structures on Pluto, both of which have been described in detail in two of my earlier papers," Cruikshank said. "They are the faulted surface complex called Virgil Fossae and the faulted region in Viking Terra, where several craters show evidence of flooding by a now-frozen liquid, surely water that came up from subsurface reservoirs, flowed over a significant area and then froze.
"Water spectral signatures are found at Virgil Fossae and Viking Terra, similar to that at Kiladze," he said.
The origins of the ammonia present at Kiladze may be from the planet's interior as well, as ammonia lowers the melting point of water, making it easier for icy "magma" to spew out of the planet's insides.
The scientists think that Kiladze is likely quite young on a cosmic scale, with the volcanic activity having occurred only within the last few million years. This is because there is no build-up of a surface layer like there is across the rest of the planet.
"The youth of the surface in and around Kiladze is estimated from the fact that
there is a constant fall-out of tiny smog particles from Pluto's atmosphere, and
estimates suggest that over the age of Pluto, as much as a 14-meter-thick layer
should have accumulated," Cruikshank said.
"Even a centimeter of two of this organic smog would mask the water ice spectral signature we observe, and from this fact, we estimate that the age of Kiladze and surroundings (since the last eruption) is only a few million years.
"At Kiladze, the last water eruption covered a lot of land area to some unknown depth, and the caldera itself has presumably undergone several episodes of eruption and collapse (into the underground void created by the removal of the erupted material)," he said.
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about cryovolcanoes? Let us know via science@newsweek.com.
Update 10/26/23, 12:07 p.m. ET: This article was updated with comment from Dale Cruikshank.
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