Why Planet 9 Still Exists

Saurav Kumar
4 min readDec 24, 2021


Virtually everyone with a TV has heard of Mickey Mouse — the familiar rodent is the mascot of the multibillion-dollar corporation, Disney. Mickey Mouse Clubhouse featured an array of animals with human-like characteristics. But there was only one main character that actually portrayed their species’ typical characteristics — Pluto, the dog. Perhaps by coincidence, our solar system shares this peculiar trait with Mickey Mouse.

Pluto and the Kuiper Belt — Image by NASA

Pluto, the dwarf planet, was believed to be a full-sized planet since 1930 (Pluto the dog’s birth year). But in 2006, scientists decided that much like its Mickey-Mouse counterpart, Pluto was different from the other planets in our solar system — it was part of a group of similar, undiscovered planets called the Kuiper Belt (NBC). Dr. Micheal Brown, Caltech researcher and @plutokiller on Twitter, presented these findings to the International Astronomical Union (IAU). After some debate, the scientific community ruled Pluto a dwarf planet.

Although Pluto was exiled as a full-sized planet, there may yet exist a 9th planet in our solar system, one that remains undiscovered to this day: Planet 9.

Clustered TNOs — Image by Astronomy Now

The search for Planet 9 begins with the Kuiper Belt. After observing the Kuiper Belt with the Hubble satellite and powerful telescopes, Dr. Brown and his partner in crime, Dr. Konstantin Batygin, found 2 Kuiper Belt bodies that were traveling abnormally far beyond Neptune — dwarf planets VP113 “Biden” (yep, it is in fact named after Joe Biden) and 90377 “Sedna.” These trans-Neptunian objects (TNOs), or objects past Neptune, were also orbiting extremely elliptical and far-out paths, prompting the question of what was causing these eccentric orbits. It turns out, if an object traveling beyond Neptune gets too close to it, Neptune will drag it and throw it far away, creating a long semi-major axis. Planet 9 did not have anything to do with long orbits — but when these bodies started stabilizing and adjusting to these extremely radical orbits, even when they were far away from Neptune, it became apparent that something was gravitationally perturbing them.

Upon finding some more TNOs, astronomers noticed that almost all of these orbits were clustered in one area. This is one of the biggest reasons the Planet 9 hypothesis became popular in the astronomical community. The chances of these orbits clustering together without gravitational disturbance were calculated at 0.007% (Caltech).

Although this seems to concretely prove Planet 9 exists, astronomers have since discovered multiple new TNOs not found in the supposed cluster. In statistics, there is a concept called selective bias — space is inconceivably vast, so objects could be anywhere — since astronomers exclusively searched for bodies near the cluster, that’s where they found them. Indeed, critics claim the clustering of TNOs is not due to Planet 9 but rather because researchers were only looking for planets near the cluster. After more statistical analysis, scientists now estimate a 25% chance that this anomaly was due to coincidence.

To learn more about the implications of these recent findings on Planet 9 research, I interviewed Dr. Batygin about his work.

Stable and Unstable TNOs — Image by Dr. Konstantin Batygin et. al

Dr. Batygin says researchers are incorrect to believe the existence of non-clustered TNOs works against the Planet 9 hypothesis, even going as far as saying, “there have not been any good counter theories, so to speak, that I’m that I’m aware of.” Dr. Batygin’s recent lecture at Brown University explains that if you actually look at the paths of the planets on non-clustered orbits, they are all dynamically unstable (Brown). Modeling out their trajectories, every single one of the unstable orbits got too close to Neptune at a point, which caused their long, elliptical, and rapidly changing orbits. In fact, by observing the semi-major axis of these orbits over time, you will find that these bodies are leaving the solar system as their orbits grow since they are so unstable. In fact, Dr. Batygin even cites that this distant belt of bodies on the edges of our solar system, called the scattered disk, now has a mass of around 1% of its original mass due to the tendency for dynamically unstable bodies to leave.

If anything, this strengthens the clustering argument for Planet 9. Looking at the dynamically stable orbits, they all still remain clustered — proving that some gravitational disturbance must be stabilizing the bodies in these unique orbits.

Planet 9 is a prevalent topic in the scientific community right now, and Dr. Batygin estimates that in a couple of years, we will know for sure whether it exists or not.

Many ask why we spend so much money on space research if we can’t afford basic necessities on Earth. But to understand the magnitude of Planet 9, you must consider the sheer amount of knowledge space hides. As Dr. Batygin says, “Nobody could have predicted what the discovery of exoplanets did for our understanding of planet formation… Nobody could have really predicted what the discovery of the Kuiper belt did… so it’s important … the exciting thing about all this is that we don’t know what is going to change, but it’s going to change something drastically.” Planet 9 is a unique object to our solar system, and it’s up to humans to find the secrets it holds.

To learn more about Planet 9, check out a book I wrote on it, available on Amazon: https://www.amazon.com/Planet-9-Greatest-Mystery-Decade/dp/B09CRTSWFR



Saurav Kumar

Hey! I'm Saurav, and I am a student from the Bay Area. I love physics, astronomy, and computer science, so I periodically write articles about concepts I like.