Philippe Reclus
The story of « Planet Y » refers to a very recent scientific hypothesis that gained major traction in late 2025.
In short: astronomers from Princeton University found evidence of a hidden, Mars-to-Earth-sized planet floating in the outer reaches of our solar system—much closer to us than the famous « Planet Nine. »
Here is the breakdown of the story and the science behind it.
1. The Discovery of the « Warp »
The hypothesis comes from a study published in August 2025 by astrophysicist Amir Siraj and his team at Princeton.
- The Clue: When looking at the Kuiper Belt (the ring of icy rocks and debris beyond Neptune), the team noticed something wrong. The orbits of objects between 80 and 200 AU (Astronomical Units) from the Sun should be relatively flat.
- The Anomaly: Instead, they found a strange 15-degree tilt or « warp » in the orbital plane of these objects. It looks as if something massive is gravitationally pulling on them.
- The Conclusion: Mathematical simulations suggest the most likely explanation for this warp is an unseen planet interacting with the belt.
2. What is Planet Y?
The team nicknamed this object « Planet Y » to distinguish it from the older « Planet X » or « Planet Nine » theories.
- Size: Likely larger than Mercury but smaller than Earth (roughly Mars-sized).
- Distance: It is predicted to orbit between 80 and 200 AU from the Sun.
- Visibility: Because it is relatively small and dark, it would be incredibly faint, explaining why we haven’t seen it with telescopes yet.
3. Planet Y vs. Planet Nine
It is important not to confuse Planet Y with « Planet Nine, » which is a separate, older theory popularized by Caltech researchers in 2016.
| Feature | Planet Y (2025 Hypothesis) | Planet Nine (2016 Hypothesis) |
| Evidence | Explains a tilt/warp in the Kuiper Belt. | Explains the clustering of distant orbits. |
| Distance | Closer (80–200 AU). | Farther (400–600+ AU). |
| Size | Small (Earth or Mars-sized). | Large (Super-Earth, ~5–10x Earth mass). |
4. What Happens Next?
Currently, Planet Y is a mathematical prediction, not a confirmed physical discovery.
- The Search: Astronomers are pinning their hopes on the Vera C. Rubin Observatory in Chile.
- Timeline: This observatory is conducting a massive 10-year survey of the sky (started around late 2025). Its camera is sensitive enough to potentially spot Planet Y directly or map enough Kuiper Belt objects to prove the « warp » is real.
Summary
The « story » is that our solar system might be more crowded than we thought. While we have been looking for a giant « Planet Nine » very far away, we may have missed a smaller « Planet Y » hiding much closer to home.
… There Might Be a Secret Planet Y Beyond Neptune …
This video is relevant because it specifically covers the recent late-2025 news regarding the Princeton study and explains the difference between the new « Planet Y » theory and the older « Planet Nine » hypothesis.