Astronomers believe they've found the "strongest" evidence yet that a mysterious ninth planet is lurking in the outer reaches of the solar system.

In a draft research paper published online this month, the scientists examined a set of "trans-Neptunian objects," or TNOs, that lie beyond Neptune and exhibit unstable movements, the Independent reported.

The best explanation for the TNOs' strange behavior is that they're being affected by an undiscovered planet, said lead author Konstantin Bogytin, a planetary science professor at the California Institute of Technology.

Bogytin told the Independentthat his team's findings represent the "strongest statistical evidence yet that Planet Nine is really out there."

Other theories considered by the researchers reportedly included the gravitational pull exerted by Neptune, the Milky Way's "galactic tide" and passing starst.

Definitive proof could come with the activation of the Vera C. Rubin Observatory being built in northern Chile, which will feature a 27 1/2-foot mirror and the largest camera ever built for astronomy and astrophysics.

"This upcoming phase of exploration promises to provide critical insights into the mysteries of our solar system's outer reaches," noted the draft research paper.

Pluto, discovered in 1930 by astronomer Clyde Tombaugh, was considered the solar system's ninth planet until it was downgraded to the status of "dwarf planet" in 2006 by the International Astronomical Union.

That move was prompted because Pluto failed to meet the requirement of having "cleared its neighboring region of other objects."