Astronomers may be closer to identifying the long-hypothesized Planet Nine, a possible giant world orbiting far beyond Neptune at the Solar System's distant frontier.
A research team led by Terry Long Phan at National Tsing Hua University compared infrared sky surveys captured 23 years apart. The analysis identified a faint object whose slow movement and brightness align with expectations for a remote planetary body.
A faint signal across decades
The researchers examined observations from the Infrared Astronomical Satellite, which surveyed the sky in 1983, and Japan's AKARI mission, which collected comparable data in 2006 and 2007. Infrared observations are particularly useful for this search because a distant planet's heat can be detected more effectively than the small amount of sunlight it reflects.
After filtering more than a million infrared sources from each survey, the team narrowed the results to one especially compelling candidate. The object appears to have shifted by 47.46 arcminutes over the 23-year interval, a motion consistent with a very distant body traveling around the Sun.
Current estimates place the possible planet between 500 and 700 astronomical units from the Sun, with a mass potentially ranging from seven to 17 times that of Earth. For comparison, one astronomical unit equals the average distance between Earth and the Sun.
Confirmation will require a clearer orbit
The finding is not yet a confirmed discovery. Two measurements separated by decades cannot establish a precise orbit, and one of the infrared readings may carry uncertainty. Planet Nine must also follow a trajectory capable of explaining the unusual alignment of several faraway objects in the outer Solar System.
Further observations with instruments such as the Dark Energy Camera on Chile's Blanco Telescope could determine whether the candidate continues along a planetary path. If confirmed, it would reshape understanding of how the Solar System formed and how much remains to be discovered in its outermost regions.
