spaceSpace and Physics

Search For Planet Nine Finds Four Candidates In Three Days


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

Neptune nine

If Planet Nine is as large as Neptune (shown here) and less than 350 times as far from the Sun as the Earth it's probably one of the four possible candidates detected in the last three days. NASA, ESA, and M.H. Wong and J. Tollefson (UC Berkeley)

Within days of the launch of a project for volunteers to identify candidates for the ninth planet, four possibilities have already been found. Even if none of these turn out to be the hypothetical planet, the search has proven exceptionally scientifically valuable and there is still more searching to be done.

Professor Brian Cox launched the Australian National University's Planet Nine search on March 28, giving anyone with access to the Internet the chance to pick through images taken by the SkyMapper telescope in search of something moving slowly enough to be at the outer edges of the Solar System. It follows on from a similar project started a month earlier to cover Northern Hemisphere skies.


The response was swift and impressive. Within days 60,000 people had classified more than 4,000,000 objects, and lead researcher Dr Brad Tucker is confident the work is good. “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. The team also rediscovered Pluto, although that still doesn't make it a planet.

The images used had been sitting unstudied for up to four years, and professional astronomers would have taken years to complete it. Tucker singled out a volunteer named Tony Roberts, who classified 12,000 observations, for praise.

The vast majority of the objects detected were either asteroids already familiar to astronomers, or could be ruled out as possible Planet Nines for other reasons. Some were space junk. Nevertheless, plenty of scientific gold was dug up. “We think we've got at least one PhD's worth out of two and a half day's work. We found several Earth-orbit crossing asteroids,” Tucker told IFLScience, which he noted dryly, “could be important for other reasons.”

So far 90 percent of the southern skies have been examined to a brightness of 19th magnitude. That means that if Planet Nine exists and is the size of Neptune or larger, and is within 350 Astronomical Units of the Sun, it should have been detected. That doesn't mean the task is over. SkyMapper is sensitive enough that detections have been made down to a magnitude of 21.7, and Tucker hopes if people keep heading over to Planet-9 on Zooinverse they can eventually pick up anything brighter than 22nd magnitude in the southern skies – extending the search to a much greater distance.


Tucker told IFLScience, Skymapper would be used to try to “recapture” the four objects of interest, after which a slightly larger telescope may be used to capture their spectrum. If any of these look like gas giants, time will be sought on one of the world's giant telescopes.


spaceSpace and Physics
  • tag
  • citizen science,

  • Planet Nine,

  • earth-crossing asteroids