This artistic rendering shows the distant view from Planet Nine back toward the Sun. Photo: Caltech/R. Hurt, January 2016

An unknown, unseen and far-off planet was identified by Caltech astronomers last January. The strange behavior of some objects in the outer reaches of our solar system could be explained by a massive body orbiting far from the sun, they hypothesized – and they invited the public to help them search the far-reaches of space to locate it.

Now four unknown objects that could be the elusive Planet 9 have been located by the 60,000 volunteers who have pored over photos of the southern sky, announced the Australian National University.

The four came from about 5 million other observations and classifications, the school said. A single volunteer made 12,000 classifications alone.

Many eyes have made short work of large swaths of the sky, the scientists 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,” said Brad Tucker, leader of the team, from ANU’s Research School of Astronomy and Astrophysics.

Volunteers are still being sought to help look at images from some of the most powerful telescopes in the world, including the aforementioned SkyMapper telescope at Australia’s Siding Spring Observatory.

“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,” said Tucker. “We’ve detected minor planets Chiron and Comacina, which demonstrates the approach we’re taking could find Planet 9 if it’s there.”

Follow-up investigation on the four candidates continues.

The Caltech researchers hypothesized that Planet 9 is very unusual for our solar system. If correct, the planet is about 56 billion miles from the sun – about 20 times farther from out star than distant Neptune, according to the researchers. A single, elliptical orbit would take the planet between 10,000 and 20,000 Earth years to complete.

The new planet would also be potentially 10 times more massive than Earth – and 5,000 times bigger than recently-demoted Pluto, they added.

“This would be a real ninth planet,” said Mike Brown, astronomy professor at Caltech, at the time of the announcement last year. “There have only been two true planets discovered since ancient times, and this would be a third.”

Brown and colleague Konstantin Batygin unveiled their discovery in the Astronomical Journal.

“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the out solar system, we become increasingly convinced that it is out there,” said Batygin. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete.”