New Paper Presents Updated Planet 9 Calculations

A new paper from Brown and Batygin reevaulates the data on Kuiper Belt Object orbits and finds that Planet 9 is still likely out there to be found.

Beth Johnson

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IMAGE: The possible orbit of Planet Nine. CREDIT: CalTech/R. Hurt (IPAC)

When it comes to scientists having a sense of humor, Caltech astrophysicist Mike Brown is one of the best, in my opinion. He is, after all, part of the team that discovered the dwarf planet Eris, so named for the goddess of strife and discord in part because of the controversy over what exactly defined a planet. That controversy led the International Astronomical Union to revise their planetary definition in 2006 and demoted Pluto to a dwarf planet as well. Dr. Brown then began using the Twitter handle plutokiller once the social media service was up and running, and his book is titled How I Killed Pluto and Why It Had It Coming.

Of course, debates about the status of Pluto still rage on the internet and among astronomers and planetary scientists. But that’s not the point of this particular story.

Just when you think Mike Brown couldn’t mess with our solar system any more than he already has, he and fellow astrophysicist Konstantin Batygin proposed back in 2016 that there might be a huge, undiscovered planet out in our solar system. The so-called Planet 9 (sorry, Pluto) is calculated to be about five times the size of Earth and ten times farther away from the Sun than Neptune. They based this hypothesis on the distribution of Kuiper Belt Objects (KBOs) and their orbits.

There is an odd clustering of these KBOs that should not happen if there isn’t another, larger body out there influencing their orbits. And those orbits should be randomly oriented with respect to the orbital plane of our solar system as well, but that’s not what we see, either. These two anomalies are what led to the calculations of the size and distance for Planet 9.

Basically, Planet 9, if it exists, is gravitationally pulling on these KBOs and has, over time, shifted their orbits into the clustering seen in the data. From the gravitational pull, you can calculate backward to the orbit of Planet 9. In fact, this is how Neptune was discovered; astronomers noted that Uranus was being pulled on by some unseen celestial body, they did…

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Beth Johnson

Planetary scientist, podcast host. Communication specialist for SETI Institute and Planetary Science Institute. Buy me a coffee: https://ko-fi.com/planetarypan