The solar system has a new ninth planet, according to evidence published by two planetary scientists, Konstantin Batygin and Mike Brown of the California Institute of Technology (Caltech) in Pasadena.

The two claim that a body nearly the size of Neptune, which has not yet been seen, has been orbiting the sun every 15,000 years, since the solar system’s infancy, 4.5 billion years ago.

The claim is "the strongest yet in the centuries-long search for a 'Planet X' beyond Neptune," reported Science magazine.

Batygin and Brown backed up their claim with detailed analyses of the orbits of other distant objects and extensive computer simulations. “If you say, ‘We have evidence for Planet X,’ almost any astronomer will say, ‘This again? These guys are clearly crazy.’ I would, too,” said Brown. “Why is this different? This is different because this time we’re right.”

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

The orbit of the inferred planet is similarly tilted, they claimed, but is extremely far from the sun. At its closest point, the planet's distance from the sun is 200 times the distance between Earth and the sun.

If Planet X is indeed eventually spotted, it would not be the first time that a planet was discovered in this way. In 1846, the French mathematician Urbain Le Verrier predicted the existence of a giant planet from irregularities in the orbit of Uranus. Astronomers at the Berlin Observatory then found the new planet, Neptune, just where it was supposed to be.