A planet-killing astronomer is now attempting to introduce a new world into the Solar System.

Self-professed “Pluto killer” Mike Brown — the Caltech professor and astronomer whose discovery of Eris in 2005 prompted the reclassification of what constitutes a full-fledged planet, thus knocking Pluto from the list a year later — is now offering up evidence for the existence of a “real” ninth planet, far beyond the orbit of Pluto and possibly even traveling farther than the Kuiper Belt extends. This “Planet Nine,” say Brown and co-researcher Konstantin Batygin — also of Caltech — could be nearly the mass of Neptune, although it has not been directly observed by any Solar System surveys performed to date.

(And for those long-time Planet X fans who will assuredly cry “told you so,” this hypothesis is based on actual observations and not just wishful thinking or sci-fi dreams. There’s a difference.)

Pluto is not the last world in the Solar System, not by a long shot. Beyond it within the Kuiper Belt exist many icy objects, some of similar size, countless others — i.e., trillions – much smaller, down to comet- and asteroid-sized. (And then of course there’s the Oort Cloud even farther out but we’re not going there.)

Observations of the orbits of a dozen of the larger recently-discovered worlds beyond Pluto, including Sedna (also discovered by Mike Brown) point to the presence of an as-yet unseen and massive object that appears to be concentrating their perihelia — that is, their closest approach points to the Sun – near a similar region. (Keep in mind that KBOs — like Pluto — tend to have highly-inclined and eccentric orbits; they aren’t aligned in a neat plane circling the Sun like the other planets… more on that here.) Brown and Batygin noticed when they reach their perihelia they all pass through the ecliptic — from south to north too — and that’s not likely just a coincidence. Something may be gravitationally shepherding the group of KBOs, and the astronomers’ models appear to implicate a ninth planet.

This incredibly distant (and apparently cold and dark) world, possibly kicked out of the planetary neighborhood just a few million years after the formation of the Solar System, would travel around the Sun in a 10,000–20,000-year-long orbit that takes it no closer than 200 A.U. (more than 4 times farther than Pluto) and as far away as 1,200 A.U.

Some astronomers aren’t ready to make the same conclusions, though. “I worry that the finding of a single new object that is not in the group would destroy the whole edifice,” said UCLA’s David Jewitt, who discovered the Kuiper Belt. “It’s a game of sticks with only six sticks.”

But Brown, in typical Plutokiller fashion, is overtly confident in the research.

“If you say, ‘We have evidence for Planet X,’ almost any astronomer will say, ‘This again? These guys are clearly crazy.’ I would, too,” Brown said. “Why is this different? This is different because this time we’re right.” (Source)

That would mean, if Brown and Batygin are indeed right, that they have discovered a new planet and that would be huge (pun intended.) But that would be something that any (every?) astronomer would love to have to his or her namesake, so one could assume a tiny bit of confidence bias. 🙂

“This would be a real ninth planet. 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.”
— Mike Brown, Richard and Barbara Rosenberg Professor of Planetary Astronomy at Caltech

That’s the news in a nutshell; I haven’t read the actual findings or attempted to go over the math myself (not that that would have done me or anyone any good – trust me.) Whether or not this pans out into something real or turns into just the latest “Search for Planet X” story remains to be seen. Further observations and analysis will be needed — some using existing data, some with telescopes that haven’t even been completed yet — to confirm these findings one way or the other. But, of course, that’s exactly how science works! You can be sure there’ll be more to come.

Read more detailed analysis by Eric Hand on Science and Alexandra Witze on Nature, and see the Caltech release here.

The findings were published today, Jan. 20, 2016, in the Astrophysical Journal.

UPDATE 1/21: Brown and Batygin have started a blog called Find Planet Nine, wherein they discuss their findings and how the astronomical population can help hunt for the purported planet. Check it out here.

UPDATE 1/22: Astrophysicist Ethan Siegel discusses why he remains skeptical about these new planetary claims on his blog at Forbes.com.