Pencil This In: Mercury’s Surface is Darkened by Graphite

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…