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

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 ...

The search for an unknown planet in our solar system has inspired astronomers for more than a century. Now, a recent study suggests a potential new candidate, which the paper’s authors have dubbed ...

Rogue planets sound like rare travelers among the stars, freed from the gravitational constraints of a host system, left to ...