We Finally Know Why Mercury Is So Dark

Something about the planet Mercury doesn’t sit right with astronomers: It’s too dark. Darker than the Moon, despite containing way less iron. But at long last, scientists have solved the mystery—and their discovery is shedding light on the fascinating past of the Solar System’s innermost planet. Mercury is slathered in graphite; the same slate-colored, carbon-based material we put in our pencils. What’s more, the patches of graphite on Mercury’s surface today may be the exposed remnants of a thick carbon crust that formed from an ancient lava ocean, according to a study published today in Nature Geoscience. continue