How a Pair Marries for the Eons

PLANETARY SCIENCEIn this week's issue of Nature , three astrophysicists suggest a way that binary Kuiper belt objects (KBOs) might have come into existence in the earliest days of the solar system with the help of gravity rather than collisions. Their proposed mechanism predicts that, as astronomers sharpen their view of the Kuiper belt, they'll find that most KBOs are tightly bound binaries, or even triplets, and that the widely separated objects seen so far are outliers.