The curious minds at What If explore what would happen if Planet X entered our solar system.

Skywatchers who spotted the Jupiter-Venus conjunction on Aug. 12 are in for a dazzling display in the night sky through the end of August, with a "planet parade" building in the eastern sky, with ...

Mike Brown is convinced that beyond Neptune, at the far reaches of our solar system, there's an unseen giant planet. "This is the 5th largest planet in our solar system, lurking out there, waiting to ...

A powerful new observatory is the best hope yet for finding the elusive Planet 9, a large planet that some scientists say is hidden in our solar... If Planet Nine is out there, this telescope might ...