Over the past century, astronomers have speculated about the existence of a mysterious 9th planet lurking in the outer ...

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 ...

There's so little we know about circumbinary planets—planets that orbit two stars instead of one—that they can feel like the stuff of fantasy. And for good reason: to date, we've only confirmed the ...

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 ...