Ninth Planet Discovered as Part of Our Solar System is Larger Than Earth

Our solar system might have just gotten another planet. Scientists have found evidence for the existence of a ninth planet beyond Pluto with a bizarre orbit in our outer solar system.

Nicknamed Planet Nine, the planet has a highly elongated orbit and a mass that's about 10 times that of Earth. It orbits about 20 times farther from the sun on average than does Neptune. In fact, it would take this planet between 10,000 and 20,000 years to make just one full orbit around the sun.

"This would be a real ninth planet," said Mike Brown, one of the researchers, in a news release. "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."

This ninth planet is estimated to be about 5,000 times the mass of Pluto, which means it would be classified as a true planet. Unlike dwarf planets, which is a category in which Pluto is included, Planet Nine gravitationally dominates its neighborhood of the solar system. In fact, it dominates a region that's larger than any of the other known planets.

"Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there," said Konstantin Batygin, one of the researchers, in a news release. "For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."

If Planet Nine does exist, it could help explain the alignment of the distant Kuiper Belt objects. It could also provide an explanation for the mysterious orbits that two of them trace.

The findings are published in the Astronomical Journal.

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