In the last few years, researchers have discovered more than 500 objects in the Kuiper belt, a gigantic outer ring in the outskirts of the solar system, beyond the orbit of Neptune. Of these, seven so far have turned out to be binaries–two objects that orbit each other. The surprise is that these binaries all seem to be pairs of widely separated objects of similar size. This is surprising because more familiar pairings, such as the Earth/moon system, tend to be unequal in size and/or rather close together. To account for these oddities, scientists from the California Institute of Technology have devised a theory of Kuiper belt binary formation.