Screengrab via Science

For decades, astronomers have wondered if a giant, mysterious planet is out there, one that orbits the sun so slowly it would force us to reimagine the solar system as we know it. Now, two astronomers have bolstered the theory, arguing that a "Planet X" would explain the otherwise mysterious behavior of six objects that exist beyond Neptune.

In a paper published in The Astronomical Journal on Wednesday, CalTech's Konstantin Batygin and Michael E. Brown argue that for the behavior of these objects to make sense, they would almost certainly have to be orbiting a planet 10 times the size of Earth. Science explains that it was their examination of these objects that convinced them that Planet X—or, as they call it, Planet 9—is probably real: 

Batygin and Brown inferred its presence from the peculiar clustering of six previously known objects that orbit beyond Neptune. They say there’s only a 0.007% chance, or about one in 15,000, that the clustering could be a coincidence. Instead, they say, a planet with the mass of 10 Earths has shepherded the six objects into their strange elliptical orbits, tilted out of the plane of the solar system.

Still, it'll take more than calculations to prove the planet's existence. TheWashington Post points out that scientists have been chasing—or scoffing at—the idea of a new planet for years. The only way to confirm the presence of this planet would be to spot it with a telescope, no easy feat. From The Post:

[Planet X] might not make its closest approach of the sun more than once every 10,000 years, and even then it would remain far beyond the known planets… It would be difficult to see the ninth planet if it's not at or near its closest approach to the sun. Brown doesn't believe the object is at that point, saying it would have been spotted by now. But he does think that the most powerful telescopes on the planet, if pointed in precisely the right direction, might be able to detect it even when it is most distant from the sun.

If it exists, the planet would be the largest in our solar system, as well as the farthest from the sun: The scientists place it at least 20 billion miles from the sun, with an orbit of between 10,000 and 20,000 years.


For Brown, the confirmation of a new planet would be a personal triumph. Brown was one of the astronomers who ejected Pluto from our solar system (no apologies there: Brown wrote a book called How I Killed Pluto and Why It Had It Coming and tweets from the handle @plutokiller) and hopes to give us one in return.

"My daughter, she's still kind of mad about Pluto being demoted, even though she was barely born at that time," Brown told the Washington Post, adding "She suggested a few years ago that she'd forgive me if I found a new planet. So I guess I've been working on this for her." Godspeed.

Danielle Wiener-Bronner is a news reporter.