Scientists analyzing the spectacular high-resolution data streaming back from NASA's New Horizons mission have discovered something curious about a crater on Pluto's largest moon, Charon.
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In the false color image of the crater above (sadly, the crater isn't really a vivid green), high concentrations of ammonia seem to accumulate in and around the Pluto-facing crater informally named Organa. The ammonia ice-filled crater appears to be unique in the observations of Charon's surface so far - the ice dramatically contrasts with the spectroscopic composition of the surrounding landscape.
The similarly-sized Skywalker crater seen just below Organa does not contain a strong ammonia ice signal and instead contains water ice, which is common on Charon.
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"Why are these two similar-looking and similar-sized craters, so near to each other, so compositionally distinct? 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," said Will Grundy, New Horizons Composition team lead from Lowell Observatory in Flagstaff, Ariz.
The ammonia-covered crater, which almost looks like a giant paintball splat, is approximately 3 miles wide - around the same size as Skywalker. But their dramatic compositional differences could reveal some fascinating science about Charon's geology.
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"This is a fantastic discovery," said Bill McKinnon, deputy lead for the New Horizons Geology, Geophysics and Imaging team from Washington University in St. Louis. "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."
In the Kuiper belt, over 40 times further away from the sun than Earth, icy volatiles reign supreme. Chemicals like ammonia have lower freezing points than other substances like water, and so the presence of quantities of ammonia could indicate active flows of icy materials from inside Charon. But did this ammonia really come from inside the moon? For now, planetary scientists aren't sure, but as more data is sent from New Horizons as it races deeper into the Kuiper belt, a better picture should form as to where Charon got its ammonia.