A Faint Dot in Old Data May Be the Solar System's Missing Ninth Planet

A Ghost in the Infrared Archives

For decades, astronomers have suspected something massive is lurking at the dark edge of our solar system — an unseen world tugging on distant objects with its gravity, leaving fingerprints everywhere but never showing its face. Now, a PhD researcher digging through decades-old satellite data may have finally spotted it. Astronomers pursuing the long-theorized Planet Nine have identified a faint, drifting object in infrared data that aligns with predictions for a massive world lurking in the outer reaches of our solar system.

The possible object was uncovered by Terry Long Phan of National Tsing Hua University in Taiwan through an unusual search strategy: rather than relying on observations gathered over nights or months, the researchers compared maps of the infrared sky produced more than two decades apart. The first dataset came from IRAS, the Infrared Astronomical Satellite, which surveyed the sky in 1983. The second came from Japan's AKARI spacecraft, which conducted its infrared survey in 2006 and 2007. The 23-year gap gave researchers a particularly long baseline: a very distant planet might barely seem to move from night to night, yet drift far enough across the sky over decades to stand out.

One Candidate Survives a Million-Source Search

After filtering more than a million sources from each dataset for brightness, location, and infrared characteristics, the team narrowed the field to 22 possible pairings, then 13, and finally one after visual inspection. That single source had shifted by 47.46 arcminutes — about one and a half times the width of the full Moon — over the 23-year span. That's an almost imperceptibly slow crawl across the sky, but exactly what you'd expect from something extraordinarily far away.

The team searched for objects between 500 and 700 astronomical units from the Sun with a mass roughly 7 to 17 times that of Earth. At 700 AU, Planet Nine would be 65 billion miles (105 billion kilometers) from the Sun. To put that in perspective, Neptune — our solar system's outermost recognized planet — sits a mere 30 AU away. The problem is that light would have to travel from the Sun to the planet and back, making a Neptune-sized planet ten times farther from the Sun some 10,000 times fainter. Infrared observations help cut through that problem: using the infrared spectrum, Planet Nine would be 100 times fainter than in visible light rather than 10,000.

Exciting, But Far From Confirmed

Phan believes his candidate has a much better claim to being Planet Nine because it was detected by both IRAS and AKARI. This is not the first time a candidate for Planet Nine has been found in infrared data. In 2021, astronomer Michael Rowan-Robinson of Imperial College, London, found an object in the IRAS data that had an estimated three to five Earth masses and was much closer to the Sun at about 225 AU. However, that detection was not confirmed and has not been made in any other dataset, such as by AKARI.

Still, scientists are urging caution. Researchers stress that Planet Nine has not been definitively discovered. While AKARI observations suggest the source shifted position over a six-month window in a manner consistent with a distant Solar System body, two positional fixes separated by decades are insufficient to calculate a reliable orbit. Caltech astronomer Mike Brown told Science that the candidate's extreme orbital tilt doesn't match predictions, which expect a tilt of only about 15 to 20 degrees. "It doesn't mean it's not there, but it means it's not Planet Nine," Brown explained.

The Hunt Is About to Get Serious

For the new candidate to become Planet Nine, astronomers would need to show that its orbit is compatible with the gravitational effects attributed to the hypothetical planet. That's a high bar — but the tools to clear it are finally arriving. Konstantin Batygin said in June 2026 that discoveries from the Vera C. Rubin Observatory would directly test every line of evidence for Planet Nine, providing "a direct test of all lines of evidence" for the hypothesis.

The Rubin Observatory boasts an 8.4-meter telescope and the largest camera ever built for astronomy research. The camera will scan the Southern Hemisphere sky every night over the next decade and is expected to access around 10 billion objects. Planet Nine's estimated brightness and distance fall within the observatory's capabilities. Whether this faint infrared dot turns out to be the solar system's long-lost ninth planet or simply another dead end, one thing is clear: after decades of searching in the dark, astronomers have never been better equipped — or more motivated — to find out.