One of the (possibly) youngest craters on Charon is also one of the most unique. Organa crater (Yep, the New Horizons team are sci-fi junkies) caught the eye of the New Horizons science team when they were looking over an infrared compositional scan of Charon.
The scan shows material in and around the crater with an infrared absorption at wavelengths of about 2.2 microns. In English? This material is rich in frozen ammonia. And it’s the only crater (so far) that is like that on Charon. The nearby Skywalker crafter features mostly water ice, like the rest of Charon’s craters and surface.
The image below shows the ammonia absorption map from the RALPH/LEISA instrument aboard the New Horizons. The ammonia is shown in green.
Ammonia absorption on Charon isn’t news. Scientists saw it through telescopes back in 2000. But the amount of ammonia found in and around this crater shocked scientists.
Organa crater doesn’t look much different than other Charon craters. Compared to the nearby Skywalker crater, both are about 3 miles in diameter and have the same bright wisps of ejected material spreading out from their craters. The one notable difference is Organa crater has a central region of darker material. But the ammonia absorption map shows ammonia-rich material extending outward from this darker material.
Where’s the ammonia coming from?
The New Horizons science team are throwing around a few ideas. Organa could just be a lot younger than other craters, and space radiation hasn’t destroyed the ammonia exposed by the meteor impact. Or, maybe whatever made the crater brought the ammonia. Or, the impactor hit a pocket of subsurface ice rich in ammonia.
If the ammonia is from Charon’s interior, it will go a long way into explaining Charon’s other surface features.
Bill McKinnon, deputy lead for the New Horizons Geology, Geophysics and Imaging team, explains why.
“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,” said McKinnon.