C lyde Tombaugh didn't set out to discover Pluto when he sent his sketches of the night sky to Lowell Observatory in ...

For the better part of a century, we believed there were nine planets in our solar system, with Pluto being the farthest from the sun. Since the discovery of more Pluto-sized dwarf planets, that ...

Pluto was always in a tough spot when it came to being a planet. Just 1,477 miles across, it's only one-fifth the diameter of Earth. It did have five known moons: Charon, Nix, ...

Clyde Tombaugh didn't set out to discover Pluto when he sent his sketches of the night sky to Lowell Observatory in Flagstaff, Arizona in 1929. More than anything, ...