Pluto was once called the ninth planet, but in 2006, scientists changed its status to a dwarf planet. A planet must clear its orbit of other objects, but Pluto shares its space with many small icy ...

And then, you have this third zone of icy dwarf planets, icy small bodies in the Kuiper Belt — and Pluto's the big one, the king of those. "In some ways, what we call it doesn't matter ...

Why was Pluto reclassified as a dwarf planet? One might think that it’s purely a matter of size. Mercury, the smallest of the ...

Last year, astronomers announced that a planet orbits Barnard’s star. Now, researchers have confirmed the existence of three more.