Planet 9 Search: Infrared Data Reveals Promising Candidates
Astronomers have identified two potential candidates for the elusive Planet Nine by sifting through archival data from the Japanese Aerospace Exploration Agency’s (JAXA) AKARI space telescope. The findings, published this month in the Publications of the Astronomical Society of Australia, represent a significant step in the ongoing search for the hypothetical planet believed to be influencing the orbits of objects in the outer solar system.
The research team, an international collaboration led by Chen et al., focused on infrared data collected by AKARI between 2006, and 2011. The strategy centered on detecting extremely cold and faint sources, invisible in visible light, that might indicate a distant, massive planetary body. AKARI’s ability to map the entire sky in infrared wavelengths proved crucial, as Planet Nine, if it exists, is expected to emit very little visible light due to its extreme distance from the sun.
The Planet Nine hypothesis originated to explain peculiar orbital characteristics observed among trans-Neptunian objects – bodies orbiting the sun beyond Neptune. These objects exhibit highly inclined and elliptical orbits that are difficult to explain without the gravitational influence of a substantial, unseen planet. Scientists have proposed that a planet with a mass between five and ten times that of Earth, located hundreds of astronomical units (AU) from the sun, could account for these orbital anomalies.
AKARI’s design, featuring a 67-centimeter mirror and cryogenic cooling using liquid helium, minimized thermal noise, allowing it to detect faint infrared sources such as star-forming nebulas and dim red giants. Despite the mission ending in 2011, its extensive archive continues to provide valuable data for astronomical research. The team combined AKARI’s all-sky catalog with dynamic simulations to narrow the search area, focusing on regions where Planet Nine would be most likely to reside based on predicted orbital models.
The researchers identified two objects whose thermal emissions and slow movement align with the characteristics expected of a distant, massive planet. Both candidates are located within the region of the sky predicted by the orbital simulations. While the findings are not a definitive confirmation, they provide compelling leads for further investigation. “A firm detection will require measuring a coherent motion and a stable thermal signature, free of spurious coincidences,” the study authors wrote.
Confirmation of Planet Nine will necessitate repeated observations to track the objects’ proper motion and parallax, establishing a consistent trajectory. Precise infrared photometry is also needed to verify their temperature and mass. Crucially, astronomers will seek to rule out any brighter counterparts in visible or deep optical light, and confirm a dynamic consistency with the observed perturbations of trans-Neptunian objects.
The next phase of the search will involve follow-up observations with more sensitive infrared telescopes, including the James Webb Space Telescope. Ground-based campaigns will also be essential to refine the objects’ orbits and eliminate the possibility of extragalactic sources. According to recent reporting from the BBC Sky at Night Magazine, evidence of Planet 9 has also been uncovered in data from the IRAS and AKARI surveys. Universe Today reported that the Solar System’s greatest mystery may finally be solved.
Confirming the existence of Planet Nine would fundamentally reshape our understanding of the solar system’s architecture, offering insights into the dispersal of icy bodies and the early migration of planets. Even a definitive non-detection, carefully quantified, would refine existing dynamic models and narrow the range of possible planetary masses.