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 ...

The number of confirmed planets outside of our solar system—known as exoplanets—has risen to 6,000, NASA has said. There is huge variety across these distant worlds, the space agency says, with ...