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Abundant ‘Mini-Neptunes’ Form New Class of Alien Planets

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.

Ground-based follow-up observations of planets found by NASA’sKepler spacecraft reveal the masses and densities of 16 new planets ranging between one and four times the size of Earth. Many of the newfound orbs, described at a meeting of the American Astronomical Society, have a rocky core surrounded by a puffed-up envelope of gas, which scientists are calling “sub-Neptunes” or “mini-Neptunes”.

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Credit: Tanya Lewis, Geoff Marcy/NASA Ames Research Center