Where did Mercury get its water ice? Maybe from a single slow asteroid impact

Mercury may have gotten much of its polar ice within a single Mercurian day following a massive asteroid impact, a new study suggests.New simulations suggest a massive impact similar to the one that formed Hokusai crater (pictured) may have, in just one Mercurian day (176 Earth days), rapidly transported water across Mercury and trapped it in permanently shadowed polar craters.