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

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.

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

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

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

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

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

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

The solar system consists of our star, the sun, and everything bound to it by gravity: the planets Mercury, Venus, Earth, ...

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.

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

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