When radar detected brightness near Mercury’s poles in 1992, the prevailing theory and hope was that it was H2O, but there are other reflective substances it might have been: lovely white sand deserts, perhaps. Messenger, the NASA probe that’s been orbiting Mercury for a couple of years now, analyzed neutrons coming from the planet, and noticed that the quantity was lower above the polar bright spots — exactly commensurate with the way water ice absorbs neutrons. Time to build a Mercury colony. [Science via New York Times]
