What is Planet Nine, and where is it? The question has fascinated astronomers for years. Scientists believe a massive ...

Astronomers have spent years searching for a possible hidden giant planet far beyond Neptune. Unusual orbits among distant ...

There have been questions about a mysterious ninth planet in our solar system for nearly a decade. Pluto was unseated as number nine in 2006. Now, a group of international researchers say they may ...

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 ...

For Planet Y and Planet Nine, that means a realistic chance of either direct detection or a clear demonstration that the outer solar system’s anomalies must be explained some other way, a promise that ...

There's a new object in the distant reaches of our solar system, and it might just offer clues to a long-standing cosmic mystery. Astronomers have cataloged a frozen minor planet called 2017 OF201, ...

In the cold, dark outskirts of planetary systems far beyond the reach of the known planets, mysterious gas giants and planetary masses silently orbit their stars—sometimes thousands of astronomical ...

A recent research paper suggests that a planet may exist far beyond Neptune — less than 20 years after the previous ninth planet, Pluto, was demoted. That research paper, accepted last month for ...

On August 24, 2006, our solar system lost a planet. It wasn't by cataclysmic destruction, but rather by the vote of the International Astronomical Union, which declared that Pluto, considered the ...

With the same data but a different statistical analysis, researchers have spotted two additional planets in a system that was already thought to host seven of them ...