Citizen scientists have flagged four objects for follow-up study in the hunt for the hypothetical Planet Nine. The four unknown objects were spotted in images of the southern sky captured recently by the SkyMapper telescope at Siding Spring Observatory in Australia. More than 60,000 people from around the world scoured these photos, making about 5 million classifications, said researchers with the Australian National University (ANU), which organized the citizen-science project. Astronomers will now use Siding Spring and other telescopes around the world to investigate the four objects to determine if they're viable Planet Nine candidates. But even if they're not, the search has still yielded valuable information, project team members said. "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," research leader Brad Tucker, from the ANU Research School of Astronomy and Astrophysics, said in a statement. "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," Tucker added. "One of those volunteers, Toby Roberts, has made 12,000 classifications."
Read More: Scientific American