What's nudging comets our way? Every so often a comet gets flung out of the Oort Cloud, a swarm of comets on the fringes of the solar system, and gets close enough to Earth for us to see it. But they don't seem to be scattered at random.

“There's an abundance of them around a great circle in the sky, and that suggests that there's something perturbing them in from this great circle.”

Jack Lissauer of NASA's Ames Research Center at the American Astronomical Society meeting in Boston. Lissauer and his colleagues have long suspected a planet-size object, sometimes called Tyche, could be hiding in the Oort Cloud.

“The model that is the simplest explanation for this is that there's a perturber in the Oort Cloud, and calculations suggest this would have to be Jupiter mass, maybe a few times the mass of Jupiter.”

A NASA spacecraft called WISE may well be able to see it. But only if Tyche isn't at the low end of its hypothetical mass range. And, of course, only if Tyche is real.

—John Matson

[The above text is an exact transcript of this podcast.]