Is there a hidden ninth planet beyond Pluto? Here’s what scientists found

After its discovery in 1930, Pluto was considered the ninth planet in our solar system. But that changed in August 2006, when the International Astronomical Union voted to reclassify it as a dwarf planet. With this, we were left with only eight planets. 

Now, some astronomers think that there could be a true ninth planet out there in our solar system, hiding from us.

The mystery started in the Kuiper Belt. This includes small, icy bodies beyond Neptune such as Pluto and Eris. While studying these distant objects, Caltech researchers Konstantin Batygin and Mike Brown noticed something unusual. 

According to their study, six of them appeared to follow similar, elongated orbits that tilt away from the flat plane where the eight known planets travel. Based on their study, the pattern could not be a coincidence. "That probability clocks in at a whopping 0.007 percent," Batygin noted.

To find out what was shaping these orbits, Batygin and Brown ran computer simulations of the outer solar system. They first ruled out the Kuiper Belt's own gravity, which meant they were looking for a single object.

If this hidden planet is out there, it could be the missing piece behind the unusual paths taken by Sedna and several other distant objects. It also explained a group of objects whose orbits run perpendicular to the plane of the solar system.

The researchers’ calculations suggest Planet Nine could weigh in at roughly five to 10 times the mass of Earth. It could also be the lightest of the gas planets as well as a super-Earth or mini-Neptune. 

Greg Laughlin of the University of California, Santa Cruz, said, "If there's going to be another planet in the solar system, I think this is it." He added, "It would be quite extraordinary if we had one. Fingers crossed. It would be amazing."

In addition to this, their model also notes that Planet Nine is very far from the Sun. Even when it gets closest to the Sun, Planet Nine could remain 200 to 300 times farther away than Earth.

"This thing is on an exceptionally frigid, long-period orbit, and probably takes on the order of 20,000 years to make one full revolution around the Sun," Batygin added. As of now, researchers have no idea where it might be along its orbit.

According to a recent study, the changes of Planet Nine existing is 40%. It’s also expected that it got flung to the outermost reaches of the solar system early on. To study the planet, a probe would need over a century to reach its theorized orbit.

“There are now five different lines of observational evidence pointing to the existence of Planet Nine,” said Konstantin Batygin. “If you were to remove this explanation, and imagine Planet Nine does not exist, then you generate more problems than you solve. All of a sudden, you have five different puzzles, and you must come up with five different theories to explain them.”