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New exoplanet: Big Earth or small Neptune?

Newly discovered Kepler 452b straddles the line between rocky and gaseous

4:01pm, August 11, 2015

MYSTERIOUS COUSIN  Superearth Kepler 452b is about 1.6 times as big as Earth and orbits a sunlike star in what scientists think is a habitable zone.

If Kepler 452b applied for the position of most Earthlike exoplanet, it would boast an impressive résumé. The newly discovered world (illustrated above) mimics our planet with a 385-day orbit around a sunlike star (SN: 8/22/15, p. 16). But there’s a hitch: Kepler 452b may not be made of rock. The planet is about 1.6 times as wide as Earth, and researchers couldn’t measure its mass. As a result, nobody knows if water on Kepler 452b has a solid surface on which to pool.

Kepler 452b is a super-Earth, falling between Earth and Neptune in girth. There are no super-Earths in our solar system but many around other stars. The ones scientists know the most about — worlds with known diameter and mass — tightly orbit stars smaller than the sun. Caltech astronomer Leslie Rogers analyzed several dozen of these

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