A curious tilt in our solar system has led researchers to believe that there may be a massive, hidden ninth planet lurking just past Neptune. 

The existence of the aptly-named Planet Nine was first brought up in January by California Institute of Technology (Caltech) scientists Konstantin Batygin and Mike Brown, according to a release.

The planets in our solar system orbit in a flat plane, roughly within a couple degrees of each other and with respect to the sun. However, the plane rotates at a six-degree tilt that makes it seem as though that the sun is at an angle, states the release.

“Because Planet Nine is so massive and has an orbit tilted compared to other planets, the solar system has no choice but to  slowly twist out of alignment,” said Caltech graduate student and lead author Elizabeth Bailey. 

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Researchers say that, although this suggested heavenly boy would be about 10 times Earth’s size, it could have been overlooked by a telescope because of its extreme distance from the sun, The Guardian reports. The scientists calculated that one year on this planet would last 17,000 years on Earth. 

Based on Brown and Batygin’s calculations, Planet Nine appears to orbit at about 30 degrees off from the other planet’s orbital plane and, in the process, influences the orbit of a large population of objects in the Kuiper Belt. It was this evidence that led them to make the discovery in the first place. 

“It continues to amaze us; every time we look carefully, we continue to find that Planet Nine explains something about the solar system that had long been a mystery,” said Batygin. 

According to the release, Planet Nine’s angular momentum is impacting the solar system due to its location and size. The angular momentum of a planet equals the mass of an object multiplied by its distance from the sun, which corresponds with the force that the planet exerts on the overall system's spin.

Because other planets in the solar system all exist along a flat plane, their angular momentum works to keep the entire disk spinning smoothly. Planet Nine’s atypical orbit adds a multi-billion-year wobble to that system. 

Brown says that mathematically, given the planet’s hypothesized size and distance, a six-degree tilt fits perfectly. However, now the question is how did Planet Nine achieve such an unusual orbit.

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Batygin suggests that it may have been ejected from the neighborhood of the gas giants by Jupiter, or it may have been influenced by the gravitational pull of other stellar bodies in the solar system’s past.  

Another team of researchers also found evidence suggesting Planet Nine’s existence, though they caution that it was by no means solid proof. 

According to The Guardian, they discovered that four objects with the longest known objects in the Kuiper Belt are most easily explained by the presence of a gigantic new planet. These “extreme” objects have elongated bits that come very close to and stray very far from the sun. It’s unlikely that they would be affected by the solar system’s larger planets. 

University of Arizona’s Renu Malhotra, who led the research team, told The Guardian that the astronomers noticed that these four objects have “very simple orbital ratios” that suggest “they are in resonances with an unseen massive planet.” 

The scientists are continuing their work with colleagues throughout the world, searching the night sky for more signs of Planet Nine. Brown says this may take three or more years. 

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