Mercury’s dark secret revealed
Graphite keeps inner planet dim
![Crater on Mercury](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2016/03/030416_cc_mystery-mercury_free.jpg?fit=860%2C460&ssl=1)
DARK PAST Akutagawa crater on Mercury is one of three craters where the MESSENGER spacecraft found deposits of carbon dug up from the planet’s original crust.
NASA, JHUAPL, Carnegie Institution of Washington