Forget Planet Nine - there could be a tenth, hidden planet in our solar system

Last year, scientists spotted signs which offered a hint that there is a huge, unseen world lurking far, far out in our solar system – ‘Planet Nine’.

But it might not be alone out there, according to new measurements of the solar system’s icy Kuiper belt – in fact, there might be a Planet Ten.

Planet Nine is thought to be 10 times more massive than Earth – and on an orbit which takes 10,000 or 20,000 years to go round the sun, according to Caltech scientists.

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But measurements of icy objects beyond Neptune hint that there might be a planet closer in – something the size of Mars, according to New Scientist.

At around 50 astronomical units (AU) from the sun, some Kuiper belt objects have orbits at 8 degrees from what they should – hinting at the existence of another planet.

‘It’s not what we expect if the only planets in our solar system are those we know of,’ says Kathryn Volk of the University of Arizona, speaking to New Scientist.

‘If it’s the size of Mars, that is a pretty big object, which would suggest it would be most likely scattered out there by planetary movements further in.’

‘It would have to be a fluke for this to not be a real effect. We think there is a real signal there and this implies an additional planet.’

It’s not proven (nor is the existence of the much more distant Planet Nine) – and the scientists aim to make further measurements to investigate.