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Scientists may have found evidence of a new Earth-like planet.

The team behind the research say the planet may be circling the Sun in an orbit past Neptune.

There are eight planets in our solar system and the order from nearest the Sun to furthest away goes: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and then a possible Planet Nine.

So what do experts have to say about this mystery?

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Several claims to have found an extra planet have been made over the years but, so far, none has proven to be true.

Now astronomers in Japan, including those from the country's National Astronomical Observatory, published their research which suggest this possible Planet Nine, could be hiding in the Kuiper Belt, much closer than previously suspected.

According to Nasa, the Kuiper Belt is a doughnut shaped region of icy bodies beyond the orbit of Neptune - the eighth and most distant planet in our solar system.

Writing in The Astronomical Journal, the researchers said: "We predict the existence of an Earth-like planet."

They found that the way that some of the objects in the Kuiper Belt behave suggests there could be a small planet among them.

The astronomers think this new planet could be three times as big as Earth but it would not have life as we know it, because the temperatures would be too cold.

The team say finding this new discovery near the Kuiper Belt, could lead to finding more possible planets.

"In conclusion, the results of the Kuiper Belt planet scenario support the existence of a yet-undiscovered planet in the far outer solar system," the researchers said.

For more than 70 years Pluto was classed as the ninth planet, until 2006, when the International Astronomical Union downgraded it to a dwarf planet.

A dwarf planet orbits the sun just like other planets, but it is smaller.