spaceSpace and Physics

Pluto Might Have A Baked Gooey Layer Under Its Surface


Jonathan O'Callaghan

Senior Staff Writer

Pluto as seen by New Horizons in July 2015. NASA/JHUAPL/SwRI

Mmmm, free goo. The icy dwarf planet Pluto wowed audiences in July 2015 when New Horizons returned stunning images of its surface. Now, we’re learning more about what’s underneath.

As reported by, this small body may have a heated layer of organic matter (mostly composed of carbon) beneath its crust. Under the right conditions, this asphalt-like layer may bake to produce amorphous carbon or granite, leading to a thick, gooey substance.


“It's not something that would be impossible inside the warmer parts of large, icy satellites and places like Pluto," Bill McKinnon from Washington University in St Louis, who presented the idea at the American Geophysical Union meeting in New Orleans in December, told

McKinnon proposed this idea as Pluto may have been able to capture organic matter when it formed, like comets in the outer Solar System. If it stored this in its crust, the heat and pressure could have left a layer of carbon 100 kilometers (60 miles) thick behind, with properties similar to hot asphalt – a liquid. It could also be solid, like graphite.

The structure of Pluto’s interior has been the subject of much debate. Back in 2016, it was theorized that there could be a huge salty ocean beneath Pluto’s heart, the oddly shaped region formally known as Sputnik Planum. Like the gooey layer, this is also thought to be about 100 kilometers (60 miles) thick.

While we can’t peer under Pluto, we can notice some effects from its interior by looking at its surface, and its interactions with its moon Charon. Specifically, this moon is tidally locked above Sputnik Planum, suggesting there is some sort of anomaly here – like, namely, an ocean.


It’s unclear if this potential liquid carbon layer and the ocean are related, or even if either exist. Much is still unknown about Pluto, and we only have the data from New Horizons’ brief flyby to go on. It might be a long time before we go back and get definitive answers to our questions.

As for New Horizons, well it’s currently on its way out of the Solar System to fly past another object, 2014 MU69, on January 1, 2019. And it’s snapping some images along the way too, including the most distant images from Earth ever taken.



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