What does a spacecraft studying Saturn have to do with the hunt for Planet 9? I’ll get to that, but first let’s recap what we know about Planet 9.

Far beyond the orbit of Neptune lies an area of space filled with objects called KBOs, or Kuiper Belt Objects. These objects are small. About the size of Pluto or smaller. But, their distribution raises interesting questions.

Researchers Konstantin Batygin and Mike Brown have a theory. There’s a ninth planet in our solar system. And it’s big. About 10 times the mass of the Earth.

How does a planet this large go undiscovered for so long? The theorized planet lies at the outer edges of our solar system. Its orbit would be about 20 times farther from the sun than Neptune. One orbit around the sun would take 10,000 – 20,000 years. I guess that’s one way to stay forever young.

Brown and Batygin noticed six KBOs following elliptical orbits pointing in the same direction in physical space. The similarities didn’t stop there. The orbits of the six objects were all tilted the same way. “Basically it shouldn’t happen randomly,” says Brown. “So we thought something else must be shaping these orbits.”

Planet 9 orbit

Planet 9 is orange. The Kuiper belt objects are magenta. The blue objects are a “predicted consequence of Planet Nine.” They are forced into right angles to Planet 9. Five known objects fit the prediction.

And that’s where Planet 9 comes in.

Cassini and Planet 9

But what does Cassini have to do with this? French astronomers were interested in what kind of effect a theorized planet that size could have on the eight known planets. For more than 10 years, Agnes Fienga, along with her team, have been developing a model called the INPOP planetary ephemerides. It’s a sophisticated model that gathers extremely accurate measurements of bodies in our solar system, including Saturn.

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Fienga and her team picked one of the orbits for Planet 9 from Brown and Batygin’s research. Then, they added the orbit to the INPOP model of the solar system.

Using measurements from NASA’s Cassini spacecraft, the French astronomers were able to reduce the search area.

Potential planet 9 location

The theorized ninth planet can’t be in the red zones because the gravity perturbations produced by the possible planet don’t match up with data from Cassini.

Now what? We still don’t know where Planet 9 is, or even if it exists. The research done by Fienga and her team help narrow down a potential area to search in. But finding it will still be tricky. We’re going to need more research and a really big telescope.

The next step will be plugging in more theorized orbits of Planet 9 to narrow the search area down even more for the theorized planet.

It’s cool to imagine a massive planet on the far edges of the solar system, but it’s still a theory at this point.

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