Could There Be A Hidden ‘Planet Y’ In Our Solar System? What We Know So Far

Astronomers may have found hints of a new planet far beyond Neptune, deep in the outer reaches of our solar system. In a study published in the Monthly Notices of the Royal Astronomical Society: Letters, researchers introduce what they are calling Planet Y, a hypothetical world suggested by the unusual tilt of distant icy objects in the Kuiper Belt.

The Kuiper Belt, a vast ring of icy bodies beyond Neptune, has long fascinated astronomers looking for hidden planets. Planet Y has not been directly seen, but its presence is inferred from the strange orbits of about 50 distant objects, which appear tilted in a way current models cannot explain.

“One explanation is the presence of an unseen planet, probably smaller than Earth but larger than Mercury, orbiting in the deep outer solar system,” said Amir Siraj, a doctoral candidate at Princeton University and lead author of the study. He emphasised that this is not a confirmed discovery of a planet, but rather the discovery of a puzzle that a hidden planet could solve.

The idea of hidden planets beyond Neptune is not new. In the early 20th century, astronomers searched for a so-called Planet X after Neptune’s discovery. Pluto, found in 1930, was once considered a candidate but was later reclassified as a dwarf planet due to its small size. Planet Y is different from the previously proposed Planet Nine, which is much larger and orbits even farther from the Sun. Siraj noted that both hypothetical planets could exist in the solar system.

Siraj’s team found that the tilt of objects beyond roughly 80 times the Earth-Sun distance is about 15 degrees. This cannot be explained by a passing star or standard planetary formation. Computer simulations showed that Planet Nine alone could not account for this tilt. Planet Y, they suggest, may have a mass between Mercury and Earth and orbit at 100 to 200 times the Earth-Sun distance, tilted at least 10 degrees relative to the known planets.

The existence of Planet Y is not yet confirmed. Siraj said the statistical significance of their findings is between 96% and 98%, which is strong but not definitive. The upcoming Vera C. Rubin Observatory in Chile, starting a 10-year sky survey this fall, may provide the proof needed.

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