Ninth Planet!!! Well….possibly….

Computer Models Predict a Massive World beyond Neptune

Planet "Nine"

This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet could be be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side.
Credit: Caltech/R. Hurt (IPAC)

The big news today involves a new world in the outer region of the solar system called the Kuiper Belt. Although it hasn’t actually been seen yet, planetary scientists at California Institute of Technology (CalTech) announced that they’ve found evidence for what may be a giant planet on a weird orbit out in the far reaches of our own solar system. Let that sink in for a moment.

If it turns out this object really exists, then it would be a candidate for planet-hood. Not only that, but it would help fill in a gap in early solar system history. It’s quite possible that this world formed as one of five planetary “cores”. Four of them ended up as Jupiter, Saturn, Uranus, and Neptune. “Core 5” could have gotten too close to one of the other gas giants early in the solar system’s history, and gotten gravitationally kicked out to its present orbit in the far reaches of the Kuiper Belt. This is all very exciting news, even if this world hasn’t quite been seen through telescopes yet.

The Skinny on “Planet Nine”

Here’s what happened. Two planetary scientists at CalTech — Konstatin Batygin and Mike Brown (who has discovered several worlds in the Kuiper Belt and is famous for claiming to have “killed” Pluto) — deduced the existence of this world by using mathematical models and computer simulations based on observational data of other worlds in the Kuiper Belt. It’s so massive they’ve nicknamed it “Fatty” (although the official “unofficial” name in their paper is “Planet Nine”). It could be the remnant of a “super-Earth” that formed early in the solar system’s history. The object has a mass about 10 times that of Earth. It orbits about 20 times farther from the Sun on average than Neptune does, andwould take between 10,000 and 20,000 years to go once around the Sun.

Finding Fatty


The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the solar system. Batygin and Brown show that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Caltech/R.Hurt (IPAC). Diagram created using Worldwide Telescope.

The road to Fatty’s discovery began when Brown noticed a peculiar effect that showed up in the orbits of 13 Kuiper Belt objects. At first, he and others who had seen this effect suspected that there was another smaller object orbiting farther out that was putting the kink in the orbits of other worlds. So, Brown and Batygin began working on computer simulations of what could be causing the effect.

To give you an idea of what’s happening, think about the orbits of the known planets. All of them move more or less in the plane of the solar system. Pluto does not — it’s on a highly elliptical and eccentric orbit (meaning it’s orbiting through the plane, not quite perpendicular). That indicates it may have been “kicked out” of its original formation region by the combined action of Jupiter or Neptune, early in solar system history.

Things get weird when you get out to the Kuiper Belt, the region where Pluto, Eris, Makemake, and other dwarf planets orbit. Six very distant KBO worlds observed by astronomers Chad Trujillo and Scott Shepherd all have elliptical orbits, which most planets do. However, those orbits “point” in the same direction, as if they all lined up together. They’re also tilted in the same direction and point about 30 degrees downward from the plane of the solar system. They’re perpendicular to the plane. The chances of both orbital “quirks” are pretty small and point to the idea that something farther out is shaping those orbits.

The concept of distant objects messing with the orbits of closer-in worlds isn’t a new one. Before Pluto was discovered, the idea of a “Planet X” sent astronomers looking for something beyond Neptune, and Clyde Tombaugh found Pluto through this search. The idea of predicting a planet’s existence with mathematics isn’t new either. Neptune was also predicted mathematically in 1846 by Urbain Le Verrier. It turned out Neptune was observed earlier, but no one realized it was a planet. In the case of this new world, if it exists, it seems to be having a gravitational impact on the six worlds closer in. So, Brown, Batygin and others are following in some hallowed and very scientific footsteps with their mathematics and computer models.

The next step was to figure out what was doing the influencing. One idea was that several distant Kuiper Belt objects (as yet unseen or undiscovered) could have enough mass and gravitational pull to mess with the orbits of the “distant six”. That idea didn’t work out because it would require quite a bit more mass in the Kuiper Belt than actually exist. About 100 times more, to be exact. So, the two scientists decidd to try doing computer simulations of the orbits using a giant world as the perturber. It worked, and they came pretty close to mimicking the weird orbits.

If this world exists, it not only explains the weirdness of the six orbits it influences, but also may be the reason why Sedna and 2012 VP (another Sedna-like world) have orbits that are a bit extraordinary as well. These and others do NOT follow orbits that would be expected of Kuiper Belt objects that were “kicked out” by gravitational interactions with Neptune early in the solar system’s history. Instead, some are quite perpendicular to the plane of the solar system, and that is likely to happen if they’re being influenced by a large, distant world.

The story is still unfolding, folks. As I’ve said several times here, this world hasn’t been observed, yet. Until it’s actually seen, we can’t even be sure it’s a planet. By IAU standards it must be self-rounded by its own gravity, orbit the Sun AND have cleared its orbit of debris. We kow it orbits the Sun. The other two aspects need to be proven.

But, its effects on the orbits of other worlds has certainly indicated something is “out there”. And that’s enough to start people looking along the path of the supposed orbit of this world to see if what’s really there. So, stay tuned! Our perception and understanding of the solar system are about to change again!

Caveat WhackJob

Now, before all the N*ancy-bots and Nibiru-huggers start spamming me with cosmic reassurances that they’ve already seen this thing coming and it’s populated with aliens with wiggly tongues or something, I want to point out again: this world has NOT been observed, yet. So, you can’t claim to have spotted it either. NO ONE has seen this world. But, trained astronomers have seen its gravitational effects on the orbits of other worlds, and eventually it will be observed. This is completely, scientifically normal and nothing to start writing conspiracy theories about.

About C.C. Petersen

I am a science writer and media producer specializing in astronomy and space science content. This blog contains news and views about these topics.
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  1. Even if this object exists, it most certainly is NOT the 9th planet. Brown is deliberately using this term to once again claim his view of what is a planet is the only legitimate view when this is far from the case. The same is true for the IAU definition, which is still rejected by many planetary scientists, largely those who hold to the geophysical planet definition and reject the notion that an object has to clear its orbit to be a planet. If this object exists, it would be at minimum the solar system’s 15th planet.

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  3. Well, to quote Monty Python And The Holy Grail, “it’s only a model”. Colour me sceptical until somebody actually sees it. I find myself wondering what process would have given it such a distant perihelion. Can there really be enough mass to interact with out there to regularise its orbit?

    I also am mildly amused that it’s being called a planet by the man who declared that planets must “clear their orbit”, since as it’s out in the Kuiper Belt, it will not have done so; so it can only be a (large) KBO. Perhaps we should designate it the Solar System’s largest comet.

  4. Yup! 😉 It’s hardly a normal orbit it’s following though, so that raises other questions. The idea that it was ejected early in solar system history has merit. However, that’s all moot until they figure out a more precise orbit for our distant possible planet friend.

    And, yes, the irony you point out in the second part of your statement has not gone unnoticed.

    Still, if it can be found, it will be an interesting discovery!

  5. Thanks for the reply Carolyn.

    If it exists, I wonder if it even came from the inner solar system. Maybe it didn’t form in the Sun’s accretion disk, but is a sub-stellar object that was picked up in the stellar nursery our sun formed from, and has been hanging around with us ever since. It’s a pretty strange orbit.

  6. If it exists, you’d want to apply Occam’s Razor and assume it’s part of the solar system. The orbit is not out of line with some long-period comets, and also there are other worlds out there closer in that were not likely captured and also have some interesting orbits. To assume capture from elsewhere assumes some more complex mechanics. It’s easier to make the assumption first that it/they formed closer in to the Sun and were ejected out dynamically during the early history of the solar system. But, until the Caltech folks actually find it (or somebody does), and can get a better handle on the orbital parameters, it’s all still an academic discussion. It’s likely out there, but finding it could be difficult. I wouldn’t be surprised if Mike Brown has some observing time somewhere to look for it. 😉

  7. Maybe the rest of us who are interested in this have or will get some observing time as well. I know I intend to pursue it. 🙂 There have also been past predictions of one or two large planets further out in the solar system; one of them was nicknamed by the scientist who proposed it as “Tyche.” It is worth looking back and comparing those proposals with this one.

  8. Anything that gets more glass pointed at the KB, the better it gets. 😉

  9. Wasn’t there a proposal that a large body in the outer solar system is responsible for perturbing comets into the inner solar system in “showers”? But is “Nine” far enough out to do that? Would there be any way to guess where in its orbit Nine is, from the orbits of known KBOs?

  10. Well, I think that’s what these next observations will do. The orbit isn’t well-characterized at this point and you really need observations of the object to nail it down. You can only get so much information by gleaning the quirks introduced into the orbits of the closer-in KBOs.

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