For the first time since Pluto was demoted, the idea of a true ninth planet is edging from speculation toward something ...

Far beyond Neptune, something heavy appears to be tugging on the outer solar system, bending the paths of distant icy worlds ...

Thanks to the discovery of thousands of exoplanets to date, we know that planets bigger than Earth but smaller than Neptune ...

Astronomers used a telescope in Hawaii to find a new object on the outer edges of our solar system, helping to fuel evidence of a long-standing theory about Planet Nine, or Planet X. For years, ...

There may be more ringed objects in the outer solar system than anyone knew. This week, researchers revealed that the egg-shaped dwarf planet Haumea — one of four known diminutive planets that circle ...

LONDON — The search for an unknown planet in our solar system has inspired astronomers for more than a century. Now, a recent study suggests a potential new candidate, which the paper's authors have ...

Astronomers photographed a baby planet, WISPIT 2b, during its formation process within a dusty ring around its star system.

A new computational model suggests that Uranus' and Neptune's cores may be less icy than their "ice giant" nickname suggests.

A team of astronomers has announced the discovery of some of the smallest planets yet detected beyond our solar system. The two newly discovered planets represent a new class of extrasolar planets, ...