Planet 9 sits at the edge of scientific imagination, promising either an epic expansion of the Solar System or a lesson in how easily patterns can mislead us. As new data arrive and old assumptions ...

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 ...

Add Yahoo as a preferred source to see more of our stories on Google. Planet Nine is a hypothesized massive planet, first proposed in 2014, that is speculated to orbit far out in the solar system. It ...

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, ...

It's an evocative idea that has long bedeviled scientists: a huge and mysterious planet is lurking in the darkness at the edge of our solar system, evading all our efforts to spot it. Some astronomers ...

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 ...