Michael Brown, professor of planetary astronomy at Caltech, is most famous for demoting Pluto from planet to planetoid—a sad but necessary consequence of his discovery that there are numerous planetoids of similar size orbiting far from the sun. His memoir, How I Killed Pluto and Why It Had It Coming, covers the rancor that led to the 2006 International Astronomical Union's vote in its disfavor.
Well, he's been looking for a true ninth planet—one big enough to have cleared its own orbit—and predicts we'll find one soon. He's even provided a map.
For their latest study, however, Brown and Batygin have added several recent observations of objects, and they've calculated that the [outer solar-system asteroid] clustering is almost certainly real — in fact, they found there is only a 0.4 percent chance that it's a fluke.
That would suggest Planet Nine is almost certainly there — and the new study includes a "treasure map" of its supposed orbit that tells astronomers the best places in the sky to look for it.
We're looking for a very cold gas planet about six times the mass of Earth and perhaps brighter than we thought a ninth planet might be, but still extremely dim and remote—some 380 times as far from the sun as the Earth. If you find one, write in.