Four possible candidates for the elusive Planet Nine have been discovered, following an intense, three-day search involving approximately 60,000 amateur astronomers, coordinated through a Zooniverse citizen science project by Siding Spring Observatory at Australian National University (ANU). In addition, the participants in the search have classified more than four million other objects.

"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," remarks ANU researcher Brad Tucker.

The existence of Planet Nine was first proposed by astronomers Chad Trujillo and Scott S. Sheppard in 2014, with the theory gaining mainstream acceptance from computer modeling done by Caltech’s Konstantin Batygin and Michael E. Brown in 2016. Both theories are based on the orbital paths of various trans-Neptunian objects, of which can only be explained by the presence of another object in the vicinity that is ten times more massive than the Earth. However, direct observation of Planet Nine has yet to occur.

Despite the probability of Planet Nine being the size of Neptune, trying to spot it is expected to be extremely difficult, as it is likely to be 1,000 times fainter than Pluto, due to its average orbital distance being nine times further out than Pluto’s. Tucker and his team are now in the process of making detailed observations of the uncovered candidates, and are encouraging amateur astronomers around the world to continue to participate in crowdsourced searches such as this.