This would be a real ninth planet, says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.There have only been two true planets discovered since ancient times, and this would be a third. It’s a pretty substantial chunk of our solar system that’s still out there to be found, which is pretty exciting.
Batygin and Brown describe their work in the current issue of the Astronomical Journal and show how Planet Nine helps explain a number of mysterious features of the field of icy objects and debris beyond Neptune known as the Kuiper Belt.Kimm Fesenmaier
Another astronomical mystery, this time a lot closer to home: does a hidden planet orbit the Sun somewhere in the distant outer reaches of the Kuiper Belt? It certainly wouldn’t be the first time someone invoked Planet X or Nemesis, usually under much more dubious circumstances. It would be exciting to discover a new planet right in our backyard, but for now I remain skeptical (as do others): the statistical significance of the orbital alignments is not high enough – usually a 5σ significance is required for a new phenomenon to become scientifically accepted. As new distant objects are discovered, their orbital parameters could reinforce this pattern – or disprove it altogether. There could be other explanations still, like the recent passage of a nearby star, disturbing the orbits in a similar manner. In the absence of direct detection in visible or infrared light, this will remain an interesting hypothesis and nothing more.