Add Yahoo as a preferred source to see more of our stories on Google. Our solar system may have a ninth planet after all, researchers say. The possibility that an additional planet may be hidden far ...

Two faint objects hiding in archival infrared sky maps now sit at the center of a growing scientific argument about whether a ...

As the United States prepares to celebrate its 250th anniversary, the history of the solar system tells its own story of ...

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 more than a century, people have wondered whether our solar system's planetary count really stops at eight. The idea ...

Scientists may have discovered a dwarf planet far beyond Neptune — an unearthing that may disprove a longstanding theory about the possibility of a giant ninth planet. The dwarf planet's existence ...

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 ...

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, ...

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 ...

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 ...

Our solar system may have a ninth planet after all, researchers say. The possibility that an additional planet may be hidden far into the solar system was touted more than a century ago. But ...