Pluto may have two ice volcanoes that spew water ice, nitrogen, ammonia, and methane onto the dwarf planet's surface, NASA announced today. The potential volcanoes were spied near Pluto's south pole, in images taken by NASA's New Horizons spacecraft during its July flyby. NASA scientists used the photos to measure the mountains; they are several miles high and tens of miles wide, with large holes in their summits. "On Earth that generally means one thing — a volcano," said Oliver White, New Horizons postdoctoral researcher at NASA’s Ames Research Center.

Scientists have seen cryovolcanoes like these before throughout our Solar System, especially on icy moons like Triton and Enceladus. They’re just like the volcanoes here on Earth, but they spew melted, icy materials rather than piping hot magma. These frozen eruptions happen when heat builds up inside the core of a moon; usually, it’s the result of a host planet pushing and pulling on a moon, creating friction and heat. When the internal pressure is high enough, the volcanoes serve as a release valve, shooting out plumes that are a hundred or more degrees warmer than the frigid surface. But when these materials make it to the surface, they quickly freeze and solidify.

Pluto’s not a moon that orbits another planet, though, so it’s not clear what the energy source is for its cryovolcanoes. There are a few ideas, though. One is that elements left over from when Pluto first formed — more than 4 billion years ago — may be radioactively decaying inside the dwarf planet, and warming things up in the process. Radioactive decay could also explain why Pluto looks to be a geologically active world. There are very few craters on the dwarf planet's surface, meaning that somehow, the surface is moving and resurfacing itself over time. That hints at a possible energy source coming from inside Pluto.

Pluto isn’t the only thing puzzling scientists — its moons behave pretty unexpectedly, too, NASA researchers also announced at the 47th Annual Meeting of the American Astronomical Society’s Division for Planetary Sciences. Pluto has one large moon, Charon, and four smaller moons: Styx, Nix, Kerberos, and Hydra. Pluto and Charon actually orbit around each other because they are pretty similar in size. The four smaller moons spin wildly around the planetary system. Hydra, for example, rotates 89 times as it completes one trip around Pluto. The moons also wobble like "spinning tops," thanks to the gravitational pulls of both Pluto and Charon. NASA thinks that the four wobbly moons are the results of mergers of two or more moons — meaning Pluto once had even more satellites than it does now.