Some scientists believe that a huge planet which has never been seen by astronomers could be lurking, almost invisibly, at the dark edges of our solar system.
Now a scientist from the California Institute of Technology (Caltech) has suggested that not only does ‘Planet Nine’ exist, it could be five times the size of Earth.
Professor Konstantin Batygin said, ‘At five Earth masses, Planet Nine is likely to be very reminiscent of a typical extrasolar super-Earth.’
Super-Earths are rocky bodies (like our planet) but much, much bigger.
Many scientists believe that there’s a large, unseen planet at the very edge of our solar system, due to the wobbly orbits of rocks beyond Neptune.
Some of the rocks out there – trans-Neptunian Objects (TNOs) – have distinctly odd orbits, which has led some scientists to believe there’s a planet out there.
But it’s likely to be extremely dim, as it’s so far from the sun, so it could be up to many years before the planet is spotted.
Bagygin and colleagues published a paper in 2016 predicting the existence of Planet Nine – and new space rocks found since that point seem to confirm that there is something out there.
Other researchers believe that there might be a huge disc of icy objects out there instead.
Batygin said, ‘ ‘While explanations other than Planet Nine may someday be found, the statistical significance of this clustering is now difficult to discount.’