Caltech scientists explain why they think our solar system has a distant Planet 9.

More evidence has emerged that a hidden giant planet may lie hidden on the fringes of our solar system.

"If there's going to be another planet in the solar system, I think this is it," Greg Laughlin of the University of California, Santa Cruz told National Geographic.

"It would be quite extraordinary if we had one. Fingers crossed. It would be amazing."

R HURT/CALTECH (IPAC) Scientists think Planet Nine may be causing disturbances in its neighbourhood.

Since the existence of Planet Nine was hinted at earlier this year, scientists has been working hard to prove the theory.

READ MORE:

* Scientists believe they've discovered new Planet 9

* Saturn's geyser-spouting moon Enceladus glows

* Astronomers discover 'super Saturn'

* Jupiter and Venus align over New Zealand

The most convincing so far is a study by scientists at the University of Arizona, who cast their gaze to the Kuiper Belt - a cold, dark realm of tiny, icy objects and the occasional dwarf planet like Pluto.

Scientists have spotted disturbances it is causing in the gravitational field of the far star system.

If the planet exists, it is thought to be about ten times as massive or three times as large as Earth.

"There have only been two true planets discovered since ancient times, and this would be a third. It's a pretty substantial chunk of our solar system that's still out there to be found, which is pretty exciting," astronomer Mike Brown said.

The last real planet to be discovered in our solar system was Neptune in 1846.

Pluto, discovered in 1930, was once the 9th planet but is now considered a dwarf planet in the Kuiper Belt.

It was visited by Earth for the first time last July; NASA's New Horizons spacecraft accomplished the first-ever flyby.

"This would be a real ninth planet," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.