Is there a ‘Planet X’?

Forget about X-ray vision and gamma ray defence beams. Planet X isn’t a superhero home world but a hypothetical 10th planet in our solar system. “I think this question tends to be intriguing because of X – the unknown,” says astronomer John Percy. “But right now, we just don’t know if there is another planet lurking on the edges of the solar system.” Percy says there are thousands of small objects orbiting the Sun beyond Neptune and Pluto. Called Kuiper Belt Objects, astronomers do not consider these to be planets because of their relatively small size – the largest, Quaoar, is half the size of Pluto. They are icy and disintegrate if diverted by another cosmic body into an orbit closer to the Sun. If this occurs, he adds, they appear to us as comets.

New Theory Accounts for Existence of Binaries in Kuiper Belt

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.