He called this hypothetical world "Planet X." "In some ways, Pluto's more of a planet than some of the other established planets, like Mercury." ...

If you answered "Pluto's planethood," your grasp of the astronomical is excellent. Feb. 18 marks the 95th anniversary of the discovery of our outermost planet-not-planet. Here's what to know about ...

Pluto isn't alone—it's part of the Kuiper Belt with possibly hundreds of other planet-sized objects. Because Pluto hasn't achieved gravitational dominance in its region, the International ...

Pluto may have lost its status as a full-fledged planet in 2006, but that doesn't mean it's a joke of a world this April Fools' Day and the folks behind Pluto TV want to make that clear.

A New Horizons image of Pluto and its moon Charon revealed more surprises about the dwarf planet and its orbiting moon. Click on the hand to see why Pluto and its moon have shaken things up.

Pluto was the little planet that could — until it couldn’t. Discovered in 1930 at Lowell Observatory in Flagstaff, Arizona, Pluto was hailed as the ninth planet in our solar system.

Pluto, discovered in 1930, was once considered the ninth planet in our solar system. In 2006, the International Astronomical Union reclassified Pluto as a dwarf planet because it doesn't meet all ...

Prague, CZECH REPUBLIC: Members of the International Astronomic Union (IAU), vote on the Resolution for Planet Definition 24 August 2006 in Prague. The resolution demoted Pluto from its status as ...