Where Did The MOON Come From?

摘要

The origin of the moon is a mystery as old as the tides. No other planet boasts such a singular and striking companion: Mercury and Venus have no moons at all, Mars has two tiny spud-shaped satellites, and the many moonlets of the gas giants are tiny in comparison with their mother planets. Pluto has, in Charon, a mate that rivals its relative size, but two or three Charons―or Pluto itself, for that matter―could fit inside the moon. Ours is bigger. Although the moon has enthralled observers for aeons, planetary scientists have struggled to trace its ancestry. The manned lunar landings of the Apollo program were supposed to help by collecting hundreds of pounds of moon rocks. Three perfectly respectable theories for lunar origin had been proposed. All that was needed to choose among them was a chunk or two of the object in question. But the lunar samples may as well have been made of blue cheese.