Expanded-color image of Mercury’s 52-km-wide Degas crater, surrounded by an abundance of curious dark stains. (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

Monochromatic and covered in craters, Mercury may outwardly resemble our Moon but the similarities abruptly end there. Ever since the MESSENGER spacecraft entered orbit around Mercury in 2011, and indeed even since Mariner 10‘s flyby in 1974, peculiar “dark spots” observed on the planet’s surface have intrigued scientists as to their composition and origin. Now, thanks to high-resolution spectral data acquired by MESSENGER during the last few months of its mission, researchers have confirmed that Mercury’s dark spots contain a form of carbon called graphite, excavated by impacts from its ancient crust.

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