Astronomers have identified a faint infrared object that shifted 47.46 arcminutes across the night sky over a 23-year period, offering a tangible target in the ongoing hunt for a hypothetical ninth planet. While researchers caution that they have not definitively discovered Planet Nine, the candidate emerged from a search through millions of sources in archival space telescope data.
Sifting Decades of Infrared Sky Surveys
Hunting for a planet hundreds of astronomical units from the Sun requires looking past visible light. At such extreme distances, reflected sunlight drops off sharply, making distant bodies virtually invisible to optical telescopes. However, planets emit thermal infrared radiation that fades much more slowly over distance. To catch this heat signature, Terry Long Phan of National Tsing Hua University in Taiwan and his colleagues compared all-sky observations from two historical space missions separated by more than two decades.
The team utilized data collected by the Infrared Astronomical Satellite (IRAS) in 1983 and Japan’s AKARI spacecraft from 2006 and 2007. Because any distant planet would move extremely slowly, a long baseline was essential to separate a true Solar System wanderer from stationary background stars. The automated software search filtered more than a million infrared sources from each survey based on brightness, location, and infrared characteristics. This process narrowed the field to 22 possible pairings, which further checks reduced to 13 candidate pairs and finally left just one solitary source.
Shifting Observations Fail to Confirm Planet Nine Trajectory
The single surviving candidate shifted by 47.46 arcminutes between the IRAS and AKARI observations, translating to roughly one and a half times the apparent width of the full Moon. Additional AKARI observations suggest the source changed position over a six-month window in a manner consistent with a distant Solar System body. Yet, two positional points separated by decades are not enough to calculate a reliable orbit. Planet Nine was originally proposed to explain the clustered and unusually tilted orbits of trans-Neptunian objects. Without a confirmed trajectory proving the candidate exerts the required gravitational influence, researchers cannot verify its identity.
Uncertainties also linger within the data itself. One of the candidate's AKARI infrared measurements appears unusually faint, suggesting it may be unreliable. The entire search relied on specific theoretical assumptions regarding Planet Nine's mass, modeled between 7 and 17 times that of Earth, and its distance, estimated between 500 and 700 astronomical units, compared to an elliptical orbit coming to around 300 astronomical units mentioned in some calculations.
Targeting the Blanco Telescope for Follow-Up Tracking
To determine whether the infrared anomaly is a true planetary body or merely a false lead, researchers plan to point more powerful instruments at the candidate’s coordinates. Phan and his colleagues propose using the Dark Energy Camera mounted on the 4-meter Blanco Telescope in Chile. Additional imaging will establish whether the object continues moving along a stable planetary orbit or vanishes entirely from the sky.
Until those observations are completed, the ninth major planet remains strictly hypothetical. Yet, after years of relying solely on mathematical inferences drawn from the gravitational footprints of outer Solar System debris, astronomers finally possess a specific point of light to investigate.
Frequently Asked Questions About the Planet Nine Candidate
What specific spacecraft provided the data used in this search?
Researchers used infrared all-sky surveys gathered by the Infrared Astronomical Satellite (IRAS) in 1983 and the Japanese AKARI spacecraft in 2006 and 2007.
How far away is the newly identified infrared candidate from the Sun?
The search targeted hypothetical objects positioned between 500 and 700 astronomical units from the Sun, where one astronomical unit equals the distance between the Earth and the Sun.
What telescope will astronomers use next to check the candidate object?
Researchers have suggested utilizing the Dark Energy Camera on the 4-meter Víctor M. Blanco Telescope located in Chile to capture follow-up observations.
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