Two faint objects hiding in archival infrared sky maps now sit at the center of a growing scientific argument about whether a massive, unseen planet orbits far beyond Neptune. Researchers mining data ...

Add Yahoo as a preferred source to see more of our stories on Google. Digital art of distant planet - Dottedhippo/Getty Images On August 24, 2006, our solar system lost a planet. It wasn't by ...

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 ...

(CNN) — 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 ...

Astronomers have identified a distant, slow-moving object in historical sky surveys that may represent a previously unknown ninth planet orbiting far beyond Neptune. The object, observed at an extreme ...