The Solar System might not be as quiet and orderly as we think. Imagine one day looking up and seeing something strange in the sky, a small speck that grows larger and larger. Soon, it becomes clear: ...

Legend has it that somewhere beyond Neptune and Pluto, there is a ninth planet, with a mass that is five times greater than ...

There's increasing evidence of another planet out there at the extreme edge of the solar system, but a new analysis suggests that may not be a planet at all. Instead, it could be a tiny black hole.

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 ...

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more. Our solar system ...

Most astronomers would love to find a planet, but Mike Brown may be the only one proud of having killed one. Thanks to his research, Pluto, the solar system’s ninth planet, was removed from 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 ...