In the depths of the solar system, far beyond Pluto, an icy world 10 times heavier than Earth might circle the sun once every 20,000 years, astronomers reported on Wednesday.
Astronomers have searched for just such a “Planet X” for more than a century, to much disappointment. But hints of such a distant world being real have intensified in the last decade, spurred by the discovery of mini-worlds in the comet belt beyond Pluto.
The new evidence comes from the stretched-out orbits of six dwarf planets that are tilted 30 degrees away from the orbits of the sun’s planets. The odds of that alignment happening by chance are about 0.0007%, according to California Insitute of Technology’s Konstantin Batygin and Mike Brown.
"Basically it shouldn't happen randomly," Brown said in a statement. "So we thought something else must be shaping these orbits."
That something is most likely a gas-covered world — “Planet 9” — that follows an elongated orbit about 20 times farther out than Neptune (which orbits 280 billion miles from the sun), the researchers concluded. Planet 9’s orbit would also explain another batch of odd mini-worlds that orbit perpendicular to the planets.
In studies published over the last few years, other astronomers have suggested such a world might exist, but the proof will have to come from a direct observation of Planet 9, Brown added. That will likely require the Hubble Space Telescope to resolve the very distant and dim world, he said on Twitter.