Pluto's moon Charon has an ammonia mystery.

Scientists combing through data collected during New Horizons' flyby of Pluto and its moons have found a very young crater awash in ammonia ice on the dwarf planet's largest moon Charon.

This chemical composition appears to be unique to the crater, based on what researchers have been able to find so far, and it may provide clues as to why Charon looks the way it does.

The ammonia-rich crater — informally named Organa, Princess Leia's surname in Star Wars — is close to another crater, called Skywalker (of course). While Organa and Skywalker are of a similar size and located in the same area of the moon, Skywalker is rich in water-ice, like other features on Charon, NASA said.

"Why are these two similar-looking and similar-sized craters, so near to each other, so compositionally distinct?" Will Grundy, New Horizons scientist, said in a statement.

"We have various ideas when it comes to the ammonia in Organa. The crater could be younger, or perhaps the impact that created it hit a pocket of ammonia-rich subsurface ice. Alternatively, maybe Organa’s impactor delivered its own ammonia."

Before New Horizons arrived at Pluto, scientists had detected ammonia at Charon, but the concentrations of the molecule that New Horizons found are unprecedented, according to NASA.

Image: NASA/JHUAPL/SwRI

Ever since New Horizons beamed back images of Pluto and Charon in July, scientists have wondered why the two worlds look to have been geologically active in the recent past. This kind of geological variation — from Pluto's ice mountains, to Charon's relatively young surface — wasn't thought possible before the New Horizons mission because of the cosmic bodies' significant distance from the sun.

This new ammonia discovery could help researchers figure out exactly why Charon looks the way it does.

“This is a fantastic discovery,” Bill McKinnon, New Horizons scientist, said in the statement. “Concentrated ammonia is a powerful antifreeze on icy worlds, and if the ammonia really is from Charon’s interior, it could help explain the formation of Charon’s surface by cryovolcanism, via the eruption of cold, ammonia-water magmas.”

New Horizons is now millions of miles past Pluto, speeding toward another object in the Kuiper Belt, but it will continue sending back data collected during its flyby of the dwarf planet for about the next year.