In 2006, the International Astronomical Union (IAU) voted on the definition of a planet. Famously, Pluto no longer met the criteria and was demoted to a dwarf planet. Things have been a bit of a mess ...

On January 5, 2005, astronomers at NASA discovered Eris, the second-largest dwarf planet in the solar system. Eris is just ...

Will Pluto have the last laugh? A group of NASA scientists hopes so. A group of members of the New Horizons mission to Pluto are making the case to redefine what constitutes as a planet to be more ...

Pluto, once considered the ninth planet, was reclassified as a dwarf planet in 2006 because it shares its orbital path with ...

Mercury is sparing us from any retrograde drama over the coming month, but October still has some retrograde energy in store. Jupiter retrograde begins on Oct. 9, and then two days later, Pluto ...