The story behind Plutos huge moon bodes well for distant ocean worlds

Unlike how scientists believe Earth's moon formed billions of years ago, Pluto and its biggest moon, Charon, didn't have a messy breakup.  

New computer simulations show the primitive dwarf planet and the object that struck it likely had an unforeseen kind of cosmic collision. Scientists usually classify planetary crashes as either hit-and-runs or graze-and-merges: One planet or rock swipes another and then keeps on trucking, or a thing smacks into another thing, and they mix together as one.