A team of astronomers says it has discovered a single slow-moving infrared object that meets all the criteria for the long-rumored ninth planet hiding behind Neptune.
The hunt for the Ninth Planet – the phantom gravitational troll of the Solar System – has been going on for a long time and is based on a special cluster of rocky bodies in the Kuiper belt beyond Neptune’s orbit. Such a cluster suggests the presence of some kind of faint massive object. But the team of authors of the new study took a new approach to the search: they examined infrared data that had been gathering dust for decades.
The study, posted this month on the arXiv preprint server and scheduled for publication in the Proceedings of the Astronomical Society of Australia, is by a team of scientists from Taiwan, Japan, and Australia. The group analyzed archived data from two infrared space telescopes, NASA‘s IRAS mission in 1983 and the Japanese AKARI satellite from 2006 to 2007. Their goal: to find any object that is cold, faint, and slow enough to be Planet Nine.
The search is based on a theory that made headlines in 2016 when astronomers Mike Brown and Konstantin Batygin of the California Institute of Technology proposed a massive, hidden planet based on clustering patterns of Kuiper Belt objects. In a 2021 update, the duo refined the theory, estimating that Planet Nine is just over six times the mass of Earth and has an orbit of 7,400 years – close enough to be detected, perhaps with the upcoming Vera Rubin Observatory.
Enter the infrared search. Astronomer Terry Long Fan of National Tsing Hua University in Taiwan and his colleagues used the 23-year gap between IRAS and AKARI to search for extremely distant objects that have moved only slightly between images. After applying filters for stars, galaxies, and other noise, they were left with one candidate. It doesn’t match any known object and appears to have moved far enough away to be considered a missing planet.
“The article is a well-executed analysis, but it is missing one thing I was hoping to see: a discussion of the likelihood that the detection is just noise or some kind of astrophysical transient that occurs close together over a 23-year period,” Brown told Gizmodo in an email.
The object’s faint signature and extremely slow motion indicate that the planet is far outside the orbit proposed by Brown and Batygin, as well as other estimates of Planet Nine. This is a new clue to the phantom object, albeit one that leads in a completely different direction.
“The other interesting thing is that the orbit of this object is not consistent with our predictions for Planet Nine,” Brown added. “That doesn’t mean it doesn’t exist, just that if it does, it’s not the predicted Planet Nine, but something unpredictable.”
“I suspect it’s just noise, but it will be interesting to find out,” he said.
So astronomers remain cautious. Two data points decades apart are not enough to pinpoint the orbit, and the source could still be an unrelated background object or data artifact. Nevertheless, the authors suggest that the object is bright enough to be rediscovered with ground-based telescopes such as the Dark Energy Camera (DECam) in Chile.
The new study also undermines some of the more fringe theories of Planet Nine – such as the idea that it is a primordial black hole – because the visible object emits light in the infrared range. If further observations confirm the presence of a planetary object, it would be a major victory for the team’s approach and confirm the long-held notion of a hidden planet in our system, albeit a different one than previously postulated.
For now, Planet Nine remains theoretical. But it could be the first real glimpse of something real-a faint point of light drifting in the darkness, waiting for our technology and ingenuity to catch it in the act of being.
