Is there a massive undiscovered planet on the outer reaches of the solar system? The idea has been around since before the discovery of Pluto in the 1930s. Labeled as planet X, prominent astronomers ...

Forbes contributors publish independent expert analyses and insights. An award-winning reporter writing about stargazing and the night sky. Is there an unseen planet — a "planet X" or "Planet Nine" — ...

Over the past century, astronomers have speculated about the existence of a mysterious 9th planet lurking in the outer ...

This video explores the ongoing search for Planet X, a hypothetical world beyond Neptune that could explain the strange ...