Astronomers analysing decades of infrared sky surveys have identified a faint, slow-moving celestial object that matches the profile of Planet Nine. The candidate, spotted after comparing data from 1983 and 2006 missions, provides researchers with their first tangible target in one of astronomy’s longest-running planetary hunts.
Several extremely distant objects exhibit clustered and unusually tilted orbits, pointing to the gravitational influence of an undetected body shephardng them from afar. This hypothetical world, widely known as Planet Nine, has remained stubbornly out of view because visible light from the Sun barely reaches the solar system’s distant frontier, making reflected sunlight virtually undetectable.
Astronomers Scan Decades of Infrared Observations For Faint Thermal Signals
Planets naturally emit heat, and infrared wavelengths fade far more slowly with distance than reflected sunlight does. Terry Long Phan of National Tsing Hua University in Taiwan led a research team that turned to thermal infrared radiation to overcome the limitations of visible light. Phan worked alongside colleagues in Taiwan, Japan, and Australia during his PhD research to comb through archival sky surveys.
The investigators compared observations from two space missions separated by a 23-year baseline. The Infrared Astronomical Satellite, known as IRAS, surveyed the sky in 1983. Japan’s AKARI spacecraft repeated the infrared survey in 2006 and 2007. Because a distant planet hundreds of astronomical units from the Sun crawls so slowly across the night sky that it appears nearly stationary from night to night, the multi-decade gap provided the necessary window to catch a subtle shift.
Computers Filter Millions of Sources Down to a Single Candidate
Out of more than a million infrared sources, the filtering process produced 22 possible pairings based on brightness, location, and infrared traits. The software searched for objects appearing in both surveys with characteristics consistent with a slow-moving body situated between 500 and 700 astronomical units from the Sun, possessing roughly 7 to 17 times the mass of Earth. Additional checks reduced that pool to 13 candidate pairs, and visual inspection ultimately left just one surviving object.
The single remaining source had shifted by 47.46 arcminutes across the sky between the IRAS and AKARI observations, a distance equal to roughly one and a half times the apparent width of the full moon.
Researchers Plan Observations to Test the Planet Candidate
Two positions separated by decades cannot reveal a reliable orbit. Despite emerging as the single best candidate from millions of sources, the discovery is not a definitive confirmation of Planet Nine.
Phan and his colleagues suggest utilizing the Dark Energy Camera on the 4-meter Blanco Telescope in Chile to determine if the source continues moving along a genuine planetary trajectory. Whether this single surviving object is truly a ninth planet or another false lead remains unverified.
