Scientists have just found something incredible lurking deep in our solar system, way past Neptune and out in the Kuiper Belt, and it could totally change how we understand our neighborhood. Scientists with the Lunar and Planetary Laboratory at the University of Arizona think they may have found an Earth or Mars-sized planet lurking out in the Kuiper Belt, which is an icy region with comets and asteroids past the orbit of Neptune.

And although you may be thinking of those reports back in January 2016 of a mysterious “Planet X” or “Planet 9” that is 25 times farther than Pluto orbiting the sun, it’s not that. This would be yet another planet we don’t now about in our solar system if true, meaning rather than eight planets orbiting the sun, there’s 10.

The scientists describe a “planetary mass object” that appears to be altering the orbits of space rocks in the Kuiper Belt, as some of the most distant Kuiper Belt Objects (KBO) are tiling away from the invariable plane of the solar system by an average of 8 degrees, indicating some mysterious force that a planet would explain.

“The most likely explanation for our results is that there is some unseen mass,” Kat Volk of the University of Arizona’s Lunar and Planetary Laboratory, or LPL, said in a statement along with fellow researcher Renu Malhotra. “According to our calculations, something as massive as Mars would be needed to cause the warp that we measured.”

“Imagine you have lots and lots of fast-spinning tops, and you give each one a slight nudge,” Malhotra said. “If you then take a snapshot of them, you will find that their spin axes will be at different orientations, but on average, they will be pointing to the local gravitational field of Earth. We expect each of the KBOs’ orbital tilt angle to be at a different orientation, but on average, they will be pointing perpendicular to the plane determined by the sun and the big planets.”