U.S. astronomers hunting for "Planet Nine" have instead stumbled on what appears to be a new dwarf planet in the solar system ...

Astronomers find evidence of a possible ninth planet beyond Neptune, reigniting the debate about the formation of the Solar ...

song, Interplanet Janet. Upon the discovery of its existence in 1930, Pluto enjoyed decades of special status as one of the solar system's planets. Then, in the summer of 2006, Pluto was demoted.

It's an evocative idea that has long bedeviled scientists: a huge and mysterious planet is lurking in the darkness at the ...

One Pluto year equals 248 Earth years. At 1473 miles in diameter—about half the width of the United States—Pluto is the ...

Learn about the recently discovered trans-Neptunian object that may eventually join Pluto as a dwarf planet, found at the edge of our solar system.

Once the quirky underdog of our solar system, Pluto held planetary status until 2006, when it got a cosmic demotion that still stings space fans. Discovered in 1930, Pluto was the ninth planet for ...

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

Astronomers have announced the discovery of a new dwarf planet in our solar system, named 2017 OF201. Located far beyond ...