CANBERRA, March 31 (Xinhua) -- Astronomers from the Australian National University (ANU) in Canberra are investigating four unknown objects which could be our Solar System's ninth planet.

Earlier this week, the ANU put a call out to 'citizen scientists' to help researchers scour thousands of images of the night sky, in the hope they might be able to discover "Planet 9".

On Friday, ANU lead researcher Dr Brad Tucker said about 60,000 people from around the world had identified more than four million objects in space as part of the ANU-led citizen search for the potential ninth planet.

"We've detected minor planets Chiron and Comacina, which demonstrates the approach we're taking could find Planet 9 if it's there," Tucker said in a statement. He said the ANU's telescope, called the SkyMapper, was crucial in ruling out areas in the southern sky where Planet 9 could be situated.

"We've managed to rule out a planet about the size of Neptune being in about 90 percent of the southern sky out to a depth of about 350 times the distance the Earth is from the Sun," Tucker said.

"With the help of tens of thousands of dedicated volunteers sifting through hundreds of thousands of images taken by SkyMapper, we have achieved four years of scientific analysis in under three days. One of those volunteers, Toby Roberts, has made 12,000 classifications."

Tucker said there was still time for 'wannabe' astronomers to get involved, by helping the ANU search the sky for Planet 9.