A simulated low-speed crash between comparably sized planetoids yields a pluto and a charon , plus an icy debris disk that could coalesce into a nix and a hydra .
Pluto has a moon , charon , half the size of the planet .
冥王星唯一的卫星卡戎，大小是冥王星的一半。
An impact has long been ____4____ for the birth of charon , the largest plutonian moon , but canup ran impact simulations to show that nix and hydra , two much smaller satellites discovered in 2005 , may be debris from the same collision .
