As evidence for a ninth planet in our solar system grows, a 30-year old theory about mass extinctions on Earth is resurfacing.

Evidence was discovered at the beginning of this year for the mysterious 'Planet Nine', and since then scientists have been looking for signs that could confirm its existence.

But the mystery of this planet has now deepened after an astrophysicist in the US has claimed this planet could have provoked comet showers that caused mass extinctions on Earth.

Yesterday, astronomer Mike Brown of Caltech, one of the scientists behind the initial announcement of the so-called 'Planet Nine', revealed he had found further evidence to support it.

This giant hidden planet is thought to sit on the edge of our solar system and is 10 times more massive than the Earth, gaseous, and similar to Uranus or Neptune.