HAWAII, 8th June, 2025 (WAM) -- American planetary scientists have ruled out the existence of the hypothetical ninth planet, commonly referred to as "Planet X", in 75 percent of the sky regions where it was previously believed to exist.
The findings follow an extensive survey of the outer solar system using the PAN-STARRS1 telescope in Hawaii, with results published on the preprint server arXiv.org.
Led by Matthew Holman of the Harvard-Smithsonian Center for Astrophysics, the team conducted one of the broadest searches to date for planet-sized bodies in distant regions of the solar system. The study identified 692 small celestial bodies, including 23 dwarf planets and 109 newly discovered objects.
Although no trace of "Planet X" or any other large body was found, the search significantly narrowed the area in which it could potentially exist.
The team used the PAN-STARRS1 telescope—originally designed to detect fast-moving objects such as asteroids and comets—to search for slow-moving planetary bodies. They developed a specialised algorithm to merge multiple images of the same sky regions taken between 2009 and 2017. By referencing known asteroids with precise orbits in the images, they were able to accurately track motion of distant objects located 80 astronomical units (AU) or more from the Sun.
None of the analysed images showed evidence of Planet X, effectively limiting its potential location to a small, unexplored region near the plane of the Milky Way galaxy—an area not yet surveyed in detail by the telescope and requiring further investigation.
The Planet X hypothesis gained momentum in 2016 when planetary scientists Konstantin Batygin and Michael Brown presented indirect evidence supporting its existence. They theorised a distant ninth planet, possibly similar in size to Neptune or Uranus, orbiting at a distance of at least 100 billion kilometres (around 670 AU) from the Sun.
Despite numerous searches, the elusive planet has yet to be observed, prompting some astronomers to question its existence and explore alternative explanations for the observed gravitational effects in the outer solar system.