Neptune-sized planet lies beyond Pluto
The solar system may host a ninth planet, much bigger than Earth and orbiting far beyond Neptune, according to research published on Wednesday.
The planet, dubbed ‘X’, has an estimated mass of about 10 times that of Earth and can bring the tally of planets in our solar system back to nine.
It is yet to be observed directly.
Astronomers at the California Institute of Technology in Pasadena said that computer simulations show that, if the mystery planet exists, it would orbit more than 50 times farther from the sun than Earth.
Professor Mike Brown, from the California Institute of Technology - who has been working on the discovery for the last two years - told ABC news: “This would be a real ninth planet.
“We noticed that the very most distant objects in our solar system ... that go out beyond Pluto they all go off in one direction, which is a very strange thing.
“It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting.”
Mike Brown, whose discovery was published in this week’s Astronomical Journal, and astronomer Konstantin Batygin, also at Caltech, were initially sceptical that such a large planet would have gone undetected for so long.
The computer model predicted the location of other objects beyond Neptune, in a region known as the Kuiper Belt.
Mike Brown's earlier research helped to demote Pluto in 2006 as the solar system’s ninth planet after other small bodies were found beyond Neptune.
Since ancient times, only two planets, Uranus and Neptune, have been discovered in our solar system.
Mike Brown said: “All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found.”