Science Astronomers discover a new kind of planet

Alien Neptune like planets discovered by NASA's Kepler spacecraft have masses and densities ranging between one and four times the size of Earth. Most of these 'mini-Neptunes' have a rocky core surrounded by a hydrogen- and helium-rich envelope.

By ,

Geoff Marcy

There's a new kind of planet to add to Kepler's cornucopia of alien worlds, and you won't find it in Earth's own solar system.