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

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

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

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 ...

And I just think it's the coolest world out there, that we know of. Brown discovered the dwarf planet Eris, a breakthrough that helped prompt a new definition of planethood. Eris is my favorite ...

In 2005, Eris was discovered. It was considered the largest known dwarf planet in the solar system until a year later when Pluto was downgraded from being a planet. In 2008, tribal violence following ...