Several decades ago, we thought the solar system had nine planets. Then Pluto was reclassified as a dwarf planet. And then astronomers realized the solar system is full of dwarf planets. Recent ...

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

Astronomers have identified a distant, slow-moving object in historical sky surveys that may represent a previously unknown ninth planet orbiting far beyond Neptune. The object, observed at an extreme ...

Add Yahoo as a preferred source to see more of our stories on Google. An illustration showing Planet Nine, a hypothetical, undiscovered planet in our solar system. New research now suggests the ...

Learn how Pluto nearly kept its planet status in a proposed 12-planet Solar System as its demotion marks its 20th anniversary. Eight days before Pluto lost its planetary status, it appeared ready to ...

Pluto is now the most well known of the outer worlds beyond Neptune—and the darling of the solar system Kayla Randall | Digital Editor, Museums A view of Pluto from NASA’s New Horizons spacecraft ...

The elusive 'Planet Nine' does exist, and may be 10 times the mass of the Earth and 20 times away from the Sun than Neptune, NASA scientists say.

On August 24, 2006, our solar system lost a planet. It wasn't by cataclysmic destruction, but rather by the vote of the International Astronomical Union, which declared that Pluto, considered the ...