An Earth-like Twin May Soon Be Found in the Solar System...

Summary

Recent research has proposed that a Planet Y may influence the orbits of trans-Neptunian objects (TNOs) beyond Neptune. The proposal is based on apparent clustering in the objects’ orbital inclinations—a shared tilt of about 15°, as described in the video—which could point to an unseen gravitational influence. This is indirect evidence, not confirmation of a planet.

The estimated mass of Planet Y depends on its distance from the Sun. The 2025 study cited in the video reportedly allows a range from roughly Pluto-sized to Earth-sized. The video gives examples of about 0.3 Earth masses at 150 AU and about one Earth mass at 225 AU. One astronomical unit (AU) is Earth’s average distance from the Sun.

Planet Y is distinct from the hypothesized Planet X, also known as Planet Nine. Planet X is expected to be more massive—around five to ten Earth masses—and farther away. The speaker notes that if Planet Y were discovered first, the numbering of these hypothetical planets might change.

A planet in the distant outer Solar System would be difficult to detect: it would be faint, move slowly across the sky, and could take thousands of years to orbit the Sun. The video estimates orbital periods of about 1,840 years at 150 AU and nearly 3,000 years at 200 AU.

The argument depends on a limited and potentially biased sample of known TNOs. The video describes 46 objects in the analysis: 33 between 80 and 200 AU, and 13 between 200 and 400 AU. Many are observed when relatively close to the Sun, where they are brighter; objects near the far ends of their elongated orbits may remain undiscovered. More complete observations could either weaken or strengthen the apparent orbital pattern.

The Vera C. Rubin Observatory is expected to expand the catalogue of distant Solar System objects through its ten-year sky survey. The speaker says early test observations detected thousands of asteroids in six weeks and anticipates many more TNO discoveries. These could help test the Planet Y and Planet X hypotheses.

The video also discusses theories of Solar System formation. Under the giant-planet migration hypothesis, the gas giants moved outward and scattered many smaller bodies. Simulations cited in the video suggest that about 99.9% of initially Pluto-sized bodies may have been ejected. Finding many additional large objects in the outer Solar System could challenge that picture, while finding few would be more consistent with it. The speaker also mentions plasma cosmology as a hypothesis, without presenting it as established scientific consensus.

Overall, the evidence remains uncertain. Orbital patterns could indicate one or more unseen planets, but they could also disappear as the sample grows and becomes more representative. Either outcome would improve understanding of the outer Solar System.

Researchers and Sources Featured

• No individual researchers are named in the subtitles.
• An unnamed 2025 research paper proposing Planet Y, which the video says will be linked in its description.
• Vera C. Rubin Observatory, for its ongoing sky survey.
• Kepler’s laws and dynamical simulations are referenced, but no specific authors or publications are identified.