Astronomers from the California Institute of Technology (Caltech) say they have strong evidence that there is a ninth planet in our Solar System orbiting far beyond even the dwarf world Pluto.
The team has no direct observations to confirm its presence just yet.
Rather, the scientists make the claim based on the way other far-flung objects are seen to move.
If proven, the putative planet would have 10 times the mass of Earth.
The Caltech astronomers have a vague idea where it ought to be on the sky, and their work is sure to fire a campaign to try to track it down.
The group’s calculations suggest the object orbits 20 times farther from the Sun on average than does the eighth – and currently outermost – planet, Neptune, which moves about 4.5 billion km from our star.
Unlike the near-circular paths traced by the main planets, this novel object would be in a highly elliptical trajectory, taking between 10,000 and 20,000 years to complete one full lap around the Sun.
The Caltech group has analyzed the movements of objects in a band of far-off icy material known as the Kuiper Belt. It is in this band that Pluto resides.
The scientists say they see distinct alignments among some members of the Kuiper Belt – and in particular two of its larger members known as Sedna and 2012 VP113. These alignments, they argue, are best explained by the existence of a hitherto unidentified large planet.
The idea that there might be a so-called Planet X moving in the distant reaches of the Solar System has been debated for more than a hundred years.