When astronomers found a large world farther out than Pluto, it became one of the final nails in the coffin of our ninth ...

For decades, Pluto was celebrated as the ninth planet of our solar system. However, in 2006, the International Astronomical ...

Pluto isn't alone—it's part of the Kuiper Belt with possibly hundreds of other planet-sized objects. Because Pluto hasn't ...

The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

And some of them looked awfully similar to Pluto. Then in 2005, astronomers discovered Eris, which estimates at the time suggested was even larger than Pluto. Mike Brown: On January 8 of this year ...

Brown is the person who discovered Eris, a 10th solar system object that's about 27% more massive than Pluto. Some astronomers disagreed with the decision, with one going so far as to call it ...

is a disc-shaped region beyond the orbit of Neptune’s in the outer solar system—50 Earth-sun distances—that’s home to dwarf planets like Pluto, Makemake and Eris. It’s also thought to be ...