Using two infrared space telescopes and a 23-year gap, scientists may have spotted a mysterious, slow-moving object beyond ...

Our solar system may have a ninth planet after all, following the declassification of Pluto nearly two decades ago, ...

A ninth planet the size of Neptune may be hidden in the far reaches of the solar system, but the evidence has left some experts skeptical.

Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about ...

The presence of another planet in the solar system could explain the odd movements of some of the bodies in the Kuiper Belt.

Researchers have found a candidate for the hypothetical Planet Nine, which could be an undiscovered giant planet way out in ...

If the object really is Planet Nine, it would be larger than Neptune and exist 700 times further from the sun than Earth.

Astronomers have long speculated about an unseen planet lurking in the solar system's outer edge. This hypothetical world, ...

This is probably the most convincing evidence for Planet Nine so far. It is believed that this planet is five to ten times ...

Researchers say they found a curious dot on infrared images taken 23 years apart that seems to be moving in a manner consistent with a large, distant planet.

A new look through decades-old data has unveiled some of the most compelling evidence yet of a hidden ninth planet in the far ...

Discovered in 1930, Pluto was long considered our Solar System's ninth planet, but was unseated in 2006 after the discovery ...