ANU astrophysicist Dr Tucker is leading the project which is being launched by Professor Brian Cox during a BBC Stargazing Live broadcast from the ANU Siding Spring Observatory.

Dr Tucker said astronomers had long discussed the likelihood of a ninth planet on the outer edges of the solar system, but nothing had been found yet.

"We have the potential to find a new planet in our solar system that no human has ever seen in our two-million-year history," he said.

Around five million people are expected to watch BBC Stargazing Live at 8pm London time from March 28 to 30 March.

In Australia the ABC will broadcast an Australian Stargazing Live program from Siding Spring from 4 to 6 April, hosted by Professor Cox and Julia Zemiro.

Dr Tucker said modern computers could not match the passion of millions of people scanning the ANU SkyMapper images of the relatively unexplored southern sky. It was a game of spot the difference.

Planet 9 is predicted to be a super Earth, about four times the size and 10 times the mass of our planet. It is also though to be cold and far away, about 800 times the distance between Earth and the sun.

"It's actually not that complicated to find Planet 9. It really is spot the difference. Then you just click on the image, mark what is different and we'll take care of the rest," Dr Tucker said.

Humble online hunting from your computer or smartphone could pay off.

Anyone who helps find the so-called Planet 9 will work with ANU astronomers to validate the discovery through the International Astronomical Union.

Dr Tucker expected people may also find other mystery objects in space, including asteroids, comets and dwarf planets like Pluto.

"If you find an asteroid or dwarf planet, you can't actually name it after yourself," Dr Tucker said.

"But you could name it after your wife, brother or sister. We need to follow all of the rules set by the International Astronomical Union."

To view the ANU's SkyMapper telescope images, visit www.planet9search.org.