A Common Sense Guide to Planet Nine

Earlier this week the California Institute of Technology announced that they had possibly discovered a new planet in the far, far distant reaches of the solar system. This has prompted wave three of the protests regarding Pluto’s planetary status, and mountains of speculation regarding the object itself. All the important information is located in the Caltech news release. Here are the important thing to remember when reading the media hype and debating online.


Artist’s depiction of a theoretical gas giant orbiting 56 billion miles from the sun.

It’s not as big as you think it is

The planet is reported as ten times larger than earth. But don’t be fooled into thinking that makes it really big. Let’s see how it measures up to the rest of the solar system first.

Jupiter is 317.83 earth masses. Saturn is 95.16. Neptune is 17.147. Uranus is 14.536. Ten earth masses definitely puts Planet Nine into the giant side of the playing field, but far from being a super-sized object, it would actually the smallest of the giants, about four earth masses smaller than Uranus, and three hundred and seven earth masses smaller than Jupiter.

Bear in mind that we have no idea what the composition of the planet is–whether it’s a gas giant or a terrestrial planet. It would be very interesting should it turn out to be terrestrial. Terrestrial planets of that size are usually found in the habitable zones of other stars and are referred to as super-earths. While Planet Nine has been referenced in media as a super-earth, it’s distance from the sun makes this appellation inaccurate. Either it’s a gas giant, or it’s something new.


None of these dwarf planets are in your astronomy book.

The Planet is Theoretical

The planet itself has not been observed in real life. Instead, it’s existence has been hypothesized based on mathematical modelling and computer simulations. Now that they have sufficient reason to believe it exists, the long tedious business of searching the sky looking for evidence of it will begin. This could take many, many years so don’t start revising your grade-school curriculum just yet.

Neptune and Pluto were all discovered because their gravitational pull caused deviations in the orbit of Uranus. Astronomers studied these anomalies, predicated a certain mass object that must be pulling them off course, and started studying the heavens looking for it. However, no matter how many new planets they find, there are still deviations that cannot be explained away. This has led scientists to look further, and further afield for the distortion.

Planet Nine, however, doesn’t solve deviations in the orbit of Neptune. Instead, it’s based on the weird orbits of six dwarf planets with unmemorable eight character designations. Should its existence be proven it will probably remain a curiosity of the Kuiper belt, rather than a significant new feature of the solar system.

Researchers Konstantin Batygin and Mike Brown who reported they hypothesis.

Researchers Konstantin Batygin and Mike Brown who reported they hypothesis.

It’s Not Pluto 2.0

Caltech Researcher Mike Brown said this regarding the theoretical planet:

“All those people who are mad that Pluto is no longer a planet can be thrilled to know that there is a real planet out there still to be found. Now we can go and find this planet and make the solar system have nine planets once again.”

The reaction, however, seems to be the opposite. Pluto supporters want Pluto back, not Pluto 2.0. Finding a new planet to appease them is like offering a new blanket to Linus. Stop calling it a New Pluto, internet. You’re not winning any friends.

But is it worth getting worked up over? Not yet. They could never find visual confirmation, or they could find out that the gravitational pull is something else entirely, like a black hole, or even more dwarf planets. The so-called Planet Nine poses no threat to Pluto’s former rank in the solar system. There’s still hope, Plutophiles.

Katie Lynn Daniels is the author of Supervillain of the Day, and the mastermind behind Vaguely Circular. She blogs about science and things that are peripherally related to science. You can read all her posts here.


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