Pluto’s largest moon, Charon, is almost as enigmatic as Pluto. As NASA’s New Horizons spacecraft helps unveil the underworldly moon, most of its features are turning out to be more puzzling than expected.

Early images showed an unexpectedly dark polar cap, which scientists think could be the result of material migrating over from Pluto. And an image released July 15 revealed that the 1,200-kilometer-wide world appears to have a surprisingly young surface with tantalizing hints of geologic activity.

“We’re flabbergasted. We really are,” says New Horizons team member Bonnie Buratti of the Jet Propulsion Laboratory. “To tell you the truth, Charon looks more like I would have expected Pluto to look.”

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