Mercury’s dark appearance may be due to ancient graphite crust
DOI: 10.1063/PT.5.029637
New Scientist : The surface of Mercury is markedly darker than predicted based on measurements of its composition. From data gathered by NASA’s MESSENGER spacecraft, Patrick Peplowski of the Johns Hopkins University and his colleagues say the darkening agent is likely carbon in the form of graphite. Scientists have proposed that carbon was deposited on the planet’s surface by comets, but Peplowski and his team say instead that the carbon may have been present since Mercury’s earliest days, when the planet was covered in a magma ocean. Although most of the minerals found on Mercury would have sunk, graphite would have floated. As the surface cooled, the researchers say, a graphite crust could have formed and then gotten buried by volcanic activity. Subsequent comet impacts would then expose the buried graphite.
