Nature reports that the New Horizons probe has snapped photos of cratered mountains that bear the hallmarks of volcanoes that erupt with ice, rather than lava:
The images show two mountains that are roughly circular in shape, with deep depressions at their centres. One of the peaks, Wright Mons, is 3–5 kilometres high, whereas the other, Piccard Mons, is up to 6 kilometres high. They resemble icy volcanoes, known as cryovolcanoes, on Neptune’s moon Triton and other frozen worlds. Flowing ice, rather than hot lava, fuels cryovolcanoes.
“We’re not yet ready to announce we have found volcanic constructs at Pluto, but these sure look suspicious, and we’re looking at them very closely,” says Jeff Moore, a planetary scientist at NASA’s Ames Research Center in Moffett Field, California, who heads the New Horizons geology team. Moore spoke on 9 November at the American Astronomical Society’s Division for Planetary Sciences meeting in National Harbor, Maryland.
If Pluto does indeed have cryovolcanoes, it would suggest that the volatile ices coating its surface can flow relatively easily both at the surface and just below it, says Robert Pappalardo, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.
Much of the rest of Pluto’s surface is geologically active, with towering mountains and smooth icy plains. All that activity suggests that some internal heat source — most likely the radioactive decay of elements left over from Pluto’s birth, 4.5 billion years ago — keeps things warm enough to flow.