Feature Astronomy

Nine Planets, or Eight?

Probing Pluto's place in the solar system

By Ron Cowen

- More than 2 years ago

Any fourth grader knows the names of the solar system’s planets. There’s Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Oh yeah, and Pluto, right?

Illustration shows the relative sizes of Varuna, Charon, and Pluto. Nature

Image of 1998 W31 and moon.