Astronomers have speculated about hidden worlds lying beyond the edge of our solar system. Presently, new work suggests the presence of a possible planetary body nicknamed Planet Y and orbiting well beyond the realm of Neptune.
Observations of Princeton University scientists focused on an unusual tilt in the pathways of icy Kuiper Belt objects. This orbital warp may suggest the presence of an undiscovered planet lying 100-200 times farther from the Sun than the Earth does.
According to lead researcher Amir Siraj, the simplest explanation holds that the disturbance originates from a small, inclined planet, which could be larger than Mercury but smaller than Earth.
Smaller than Earth but larger than Mercury, #PrincetonU‘s @TheAmirSiraj and colleagues may have discovered a hidden planet orbiting 100-200 times farther from the Sun than Earth — Planet Y. https://t.co/cwlewVUc5c
— Princeton University (@Princeton) August 25, 2025
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How Planet Y Differs from Planet Nine
The idea for a faraway hidden planet is not new. For almost a decade now and astronomers have discussed the existence of Planet Nine, a supposed massive body about ten times the mass of Earth and far beyond the orbit of Neptune.
Planet Nine is meant to explain the clustering of distant icy orbits, Planet Y seems to solve the puzzle of why certain Kuiper Belt objects are tilted about 15 degrees from what is known as the main orbital plane of the solar system. Researchers point out that it is possible for both planets to exist, with each one affecting the outer solar system in differing ways.
Could This Mysterious World Be Real?
Astronomical simulations suggest that Planet Y is a credible possibility. The models show that a world with a mass anywhere between Mercury and Earth could create the observed tilt without disturbing anything close by in the solar system. Most scientists think such a planet formed in the inner solar system billions of years ago and was subsequently pushed outward by gravitational encounters with giant planets.
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“The truth is, we still know very little about the region beyond Neptune,” said astronomer Jonti Horner, who believes the idea is scientifically plausible.
The Search Ahead
Vera C. Rubin Observatory in Chile could provide the key to unlocking this cosmic mystery. It is to begin a decade long sky survey in which it will map thousands of trans Neptunian objects with unprecedented detail. If Planet Y exists and the gravitational effects exerted on nearby objects and perhaps even the planet itself could be directly observed within the next few years.
History confirms that the planets Neptune and Pluto were established in part due to subtle orbital anomalies. If found to exist, Planet Y would thus not only increase our solar system family of planets but give a new perspective on how worlds are formed and scattered spatially.
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