Caltech astronomer Mike Brown broke many hearts as his research was the reason why Pluto was downgraded to a dwarf planet, but his latest discovery could re-establish a nine-planet solar system. In a study released Wednesday, Brown and astronomer Konstantin Batygin determined a mysterious planet was responsible for the erratic movement of objects in the outer solar system's Kuiper Belt.
They concluded the movements were caused by a massive planet with a bizarre orbit.
Planet Nine —as the newly discovered object is temporarily called by the astronomers (or Planet X by others) — could be between 5 and 20 times more massive than Earth with an orbital period that would take 10,000 to 20,000 years to complete one journey around the sun.
"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," Brown, an astronomy professor at the California Institute of Tecnology, said in a statement. The research was published in the Astronomical Journal.
OK, OK, I am now willing to admit: I DO believe that the solar system has nine planets.
— Mike Brown (@plutokiller) January 20, 2016
Brown's previous discovery of an object later called Eris prompted a revision in how planets are classified by the International Astronomical Union in 2006. Planet Nine would have no such worries about classification as it has 5,000 times the mass of Pluto. The main reason why Pluto was demoted was because it lacks sufficient mass to clear its neighborhood of smaller objects, but Planet Nine fulfills that requirement set forth by the IAU.
The discovery of Planet Nine began with an observation by astronomers Chad Trujillo, a former postdoctoral student of Brown's and Scott Sheppard. Trujillo and Sheppard discovered 13 Kuiper Belt Objects had a similar orbital anomaly. Brown and Batygin soon found six of those objects had an elliptical orbit that start at a fixed location whereas their outer orbits moved around.
"It's almost like having six hands on a clock all moving at different rates, and when you happen to look up, they're all in exactly the same place," Brown said. The astronomers ruled out a random coincidence and focused on likely suspects for this behavior. Nothing worked except for the influence of a massive planet.
Planet Nine was discovered to have what is called an anti-aligned orbit, where its closest approach to the sun, the perihelion, is 180 degrees across other observed perihelions, according to Brown.
Simulations using this orbit matched what the astronomers observed, but also explained the eccentric orbit of possible dwarf planets Sedna, discovered by Brown, and 2012 VP 113, discovered by Trujillo and Shepherd.
The final piece of the puzzle that led Brown to conclude what they discovered was a planet was evidence of KBOs following a perpendicular path from Neptune that matched the simulation. "With the existence of the planet also explaining these perpendicular orbits, not only do you kill two birds, you also take down a bird that you didn't realize was sitting in a nearby tree," Batygin said.
Brown summed up his discovery on his blog. "I was wrong," Brown said in response to his assured stance that there were eight — and only eight — planets in the solar system.
For now, Brown and Batygin's work is a prediction, not definitive proof of a Planet X. There needs to be an observation of the mysterious object. Earth-based telescopes such as the W.M. Keck Observatory and the Subaru Telescope, both located on Mauna Kea in Hawaii, or the Hubble Space Telescope could observe Planet Nine once astronomers further refine its orbit.
For the time being, the possible evidence of a Planet Nine opens up a lot of intriguing possibilities. The planet could have been a hypothetical fifth giant core ejected from the solar system. The size of the planet adds another common planet type to our solar system, which would make it more normal, according to Batygin.