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Pluto has huge ice volcanoes that may still be active to this day. A comprehensive analysis of data from NASA’s New Horizons spacecraft, which flew past Pluto in 2015, has revealed that a large area of its surface – at least 180,000 square kilometres – is made up of ice that seeped out from underground via cryovolcanism relatively recently.

This area, surrounding two mountains called Wright Mons and Piccard Mons, is made up of undulating hummocks of ice that seem to be unique to Pluto. “There’s not really anything anywhere else in the solar system that looks like this,” says at the Southwest Research Institute in Colorado. “They’re very rough, they’re very bouldery, blocky, bumpy, lumpy – it would be a tough hike.”

Singer and her colleagues examined images, composition data and topographical maps of the area to determine how this unique terrain formed. They found that it was probably created via what is called effusive cryovolcanism, with liquid or relatively soft ice seeping out from underground to gradually create huge mountains and overlapping mounds. While Wright Mons and Piccard Mons appear to be cryovolcanoes at least as large as the biggest active volcanoes on Earth, there is no evidence of explosive volcanic eruption, just slow, effusive seeping.

The overlapping nature of the hummocks indicates that there were probably multiple episodes of volcanism over time, and the lack of impact craters hints that this happened relatively recently. “It’s all relatively young,” says Singer. “It probably formed within the last couple hundred million years, but we’re not sure if it’s still ongoing.”

This large a volcanic landscape means that cryovolcanoes had to spew out more than 1000 cubic kilometres of ice in this area. This amount of cryovolcanism would require Pluto’s insides to be hotter than researchers expected based on what we know of its interior structure. “We just don’t have a great understanding of how these smaller solar system bodies can have this active geology and they aren’t just cold and dead,” says Singer.

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