The Planet Y theory proposes the existence of a previously unknown Earth-sized planet lurking in the outer solar system, potentially much closer to Earth than the hypothesized Planet Nine. This new candidate was suggested by a team of Princeton astrophysicists after analyzing the orbits of Kuiper Belt objects (KBOs), which revealed an unexpected tilt that existing models could not explain.
Discovery and Evidence Behind Planet Y
Using data from 50 KBOs, researchers found their orbits were tilted by about 15 degrees relative to the plane of the known planets. The team concluded that such a warp is best explained by the gravitational influence of an unseen planet, which they named Planet Y. This planet is estimated to orbit between 100 and 200 astronomical units (AU) from the Sun — roughly twice as close as the proposed Planet Nine — and is thought to be similar in size to Earth or slightly smaller, somewhere between Mercury and Earth in scale.
Unlike Planet Nine, which is hypothesized to be a super-Earth or mini-Neptune several times Earth’s mass and much farther away, Planet Y’s closer proximity and smaller size might make it detectable within the next few years through dedicated astronomical surveys.
Implications and Ongoing Search
The Planet Y hypothesis does not negate the Planet Nine theory but suggests a more complex architecture of the solar system’s outer region, potentially increasing the number of major planetary bodies beyond Neptune. While the existence of Planet Y remains unconfirmed and some experts remain skeptical, the study provides a compelling puzzle driving further observational efforts.
Lead author Amir Siraj emphasized that the paper presents a strong indication rather than a definitive discovery, highlighting science’s iterative nature in unraveling cosmic mysteries. The search for Planet Y continues, promising to enhance our understanding of the solar system’s boundaries and the dynamics of distant objects within the Kuiper Belt.