Astronomers analyzing decades-old archival data have identified a faint, slow-moving object that matches the mathematical profile of Planet Nine, a hypothetical world thought to inhabit the outer edges of our Solar System.
The 23-Year Baseline and the Infrared Search for Faint Targets
The vast and lightless frontier of the outer Solar System makes finding distant bodies exceptionally difficult. While thousands of alien planets have been detected orbiting distant star systems, locating objects on our own backyard’s perimeter is hampered by extreme distance and the absence of direct sunlight.
To overcome this, Terry Long Phan of National Tsing Hua University in Taiwan and his colleagues turned to thermal infrared radiation. A planet situated hundreds of astronomical units away reflects very little visible light, but it still emits heat. Infrared wavelengths fade much more slowly over vast distances than reflected sunlight.
Phan and his research team compared sky surveys conducted decades apart to isolate objects moving with the glacial pace expected of a distant planetary body. They utilized data from the Infrared Astronomical Satellite (IRAS), which mapped the sky in 1983, and Japan’s AKARI spacecraft, which repeated the infrared survey in 2006 and 2007. The resulting 23-year baseline provided a sufficiently long window for a remote world to register a measurable drift across the sky.
Filtering Over a Million Sources Down to One Candidate Pair
Sifting through the immense volume of archival data required rigorous automated filtering. The research team searched for sources appearing in both the IRAS and AKARI datasets at positions consistent with an object located between 500 and 700 astronomical units from the Sun, possessing a mass roughly 7 to 17 times that of Earth.
After filtering more than a million infrared sources from each mission based on brightness, location, and infrared characteristics, the automated process yielded 22 possible pairings. Additional verification checks reduced that number to 13. Visual inspection of the remaining candidates left just a single source.
According to the findings, this apparent source shifted by 47.46 arcminutes between the IRAS and AKARI observations. That angular displacement spans approximately one and a half times the apparent width of the full Moon.
Remaining Uncertainties and the Lack of a Confirmed Orbit
Despite the tantalizing trajectory, 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.
Planet Nine was originally hypothesized to account for the unusual gravitational clustering and orbital tilts observed among extreme trans-Neptunian objects. For this new candidate to be confirmed as that shepherding world, it must travel along a specific orbital path capable of exerting that exact gravitational influence.
Uncertainties also remain regarding the data itself. One of the candidate’s AKARI infrared measurements appears unusually faint and may be unreliable. Furthermore, the search algorithms relied heavily on assumptions regarding the hypothetical planet’s mass, temperature, density, and distance. A smaller, colder, or more distant object could have escaped these surveys entirely.
Next Steps with the Blanco Telescope in Chile
Resolving the status of this infrared candidate requires targeted follow-up observations. Phan and his colleagues have proposed utilizing the Dark Energy Camera on the 4-meter Blanco Telescope in Chile. Additional imaging will determine whether the faint point of light continues along a legitimate planetary trajectory or vanishes as another false lead.
For now, Planet Nine remains hypothetical. Yet, after years of relying solely on the inferred gravitational footprints left on distant icy bodies, astronomers finally possess a specific, tangible target to track across the night sky.
