At a Glance
- Astronomers are hunting for a hidden ‘Planet Nine’ whose gravity is believed to cause the unusual, clustered orbits of icy bodies found far beyond the planet Neptune.
- Researchers pioneered a new search method by analyzing archival infrared data from the AKARI space telescope, searching for the planet’s faint internal heat signature rather than its reflected sunlight.
- The team focused on a computer-modeled region of space, removing known celestial objects and searching for a body that remained stationary over 24 hours but moved over months.
- This meticulous analysis yielded two potential candidates for Planet Nine whose observed positions and brightness levels align with current theoretical predictions for the undiscovered world.
- These compelling candidates now require follow-up observations with more powerful telescopes to track their movement and confirm if one is truly our solar system’s ninth planet.
For years, astronomers have pointed to the peculiar, clustered orbits of icy bodies beyond Neptune as evidence for a hidden world lurking in the outer solar system. This theoretical world, dubbed ‘Planet Nine,’ is thought to be a massive planet whose gravity is shepherding these distant objects. However, finding it has proven exceptionally difficult. Now, a new analysis of archival data has revealed two potential candidates, not by looking for faint, reflected sunlight but by searching for the planet’s intrinsic heat.
The challenge in spotting Planet Nine with traditional telescopes lies in its extreme distance. An object’s brightness from reflected sunlight decreases with the fourth power of its distance from the sun, meaning that if it were twice as far away, it would be 16 times fainter. However, the heat an object radiates, known as thermal or black body radiation, fades less dramatically, decreasing with the square of the distance. This crucial difference in physics prompted researchers to take a new approach, hunting for Planet Nine’s faint thermal glow in the far-infrared part of the spectrum using data from the Japanese AKARI space telescope, which completed the most sensitive all-sky survey to date in these wavelengths.
The scientific team focused its search on a promising patch of the sky between 30 and 50 degrees right ascension, an area suggested by computer models that simulate Planet Nine’s gravitational influence. To isolate their target, the researchers designed a meticulous filtering process. First, they cross-referenced the AKARI data with nine other astronomical catalogs to eliminate all known stars, galaxies, and asteroids. They then screened for objects with a specific motion profile: something that would appear stationary in observations taken within 24 hours but would have moved noticeably over six months, a pattern consistent with a slow-moving, distant planet.
After carefully removing false positives caused by cosmic rays and background galactic dust, the analysis yielded two promising candidates in its results published in the Publications of the Astronomical Society of Australia. The positions and brightness of these two sources fall within the range predicted for Planet Nine, a gas or ice giant estimated to be five to 10 times the mass of Earth. While these findings do not represent a definitive discovery, they are compelling leads that warrant further investigation. Follow-up observations are now needed to track these objects and determine if their movement confirms the existence of a new, giant planet in our solar system’s dark frontier.
References
- Chen, A. Y. A., Goto, T., Yamamura, I., Nakagawa, T., Wu, C. K.-W., Phan, T. L., Hashimoto, T., Uno, Y., Ho, S. C.-C., & Kim, S. J. (2025). A far-infrared search for planet nine using AKARI all-sky survey. Publications of the Astronomical Society of Australia, 42, e061. https://doi.org/10.1017/pasa.2025.10037
- Thompson, M. & Universe Today. (2025, June 20). The solar system’s greatest mystery may finally be solved. Phys.Org; Universe Today. https://phys.org/news/2025-06-solar-greatest-mystery.html
