While Planet Y has been not yet been directly observed, unexpected inclinations found in the orbits of roughly 50 distant objects in the Kuiper Belt, suggest the presence of an “unseen” planet.
Published: October 4, 2025 7:47 PM IST
Planet Y: In a remarkable discovery that could reshape the prevalent scientific view of our solar system, astronomers have found evidence of a ‘hidden’ planet on the outskirts of our cosmic neighborhood. The evidence of a mysterious celestial body, dubbed ‘Planet Y’, was inferred from the unusual tilt of distant objects in the Kuiper Belt, according to a study published in the Monthly Notices of the Royal Astronomical Society: Letters.
Where is Planet Y?
As per researchers, while Planet Y has been not yet been directly observed, unexpected inclinations found in the orbits of roughly 50 distant objects in the Kuiper Belt, suggest the presence of an “unseen” planet, believed to be smaller than the Earth, in the far reaches of our solar system.
“One explanation is the presence of an unseen planet, probably smaller than the Earth and probably bigger than Mercury, orbiting in the deep outer solar system. This paper is not a discovery of a planet, but it’s certainly the discovery of a puzzle for which a planet is a likely solution.” said Amir Siraj, a doctoral candidate at Princeton University and lead author of the study, according to CNN.
According to the study, their hypothetical Planet Y is distinct from the previously proposed Planet Nine, which is believed to be around 5-10 times more massive than Earth, and orbiting much farther out. Siraj believes that both planets could exist in our solar system.
How Planet Y was found?
Siraj revealed that Planet Nine served as the motivation for the team to investigate the presence of more planets in the Kuiper Belt, a vast ring of icy bodies beyond Neptune, which has long intrigued astronomers searching for hidden planets.
The researchers observed that the tilt located about 80 times the Earth-Sun distance is around 15 degrees, which could not be explained by the passing star or standard planetary formation models. “It was quite a surprise to find that the solar system suddenly appears to be tilted by about 15 degrees, and this is what sparked the Planet Y hypothesis,” Siraj said.
The study, based on computer simulations, noted that none of the existing models, including the presence of the hypothetical Planet Nine, could not account for tilt, and suggested the presence of a planet. As per the study, Planet Y, could have a mass ranging between Mercury and Earth, and orbits at 100 to 200 times the Earth-Sun distance, with an orbital tilt of at least 10 degrees relative to the known planets.
Scientists believe the presence of Planet Y will be confirmed within the next 2-3 years as Chile’s Vera C. Rubin Observatory is set to begin its 10-year survey later this year, which could definitive evidence of a ninth planet in our solar system.
