The solar system lost its ninth planet back when Pluto was demoted to a dwarf planet, but research might indicate that there ...

Is there a massive undiscovered planet on the outer reaches of the solar system? The idea has been around since before the discovery of Pluto in the 1930s. Labeled as planet X, prominent astronomers ...

Mercury, Venus, Earth, Mars...When you hear the names in order, some of you might think, "I learned that in school."But doesn't the Moon belong to that group?Does asteroid just mean a small ...

Add Yahoo as a preferred source to see more of our stories on Google. Digital art of distant planet - Dottedhippo/Getty Images On August 24, 2006, our solar system lost a planet. It wasn't by ...