An Earth-sized hell circles faraway star

The recently discovered, very hot rocky planet is the smallest with known diameter and mass

By Gabriel Popkin, 12:43 PM October 30, 2013

A distant Earth-sized planet’s density suggests it is made of the same stuff as Earth. The planet, named Kepler-78b, is the smallest exoplanet for which researchers know both size and mass.

Kepler-78b, detected this year in data from NASA’s now-crippled Kepler spacecraft, is located 700 light-years from Earth in the constellation Cygnus. The planet’s gravitational tug causes its star to shimmy back and forth slightly, which compresses or expands the wavelengths of light the star emits. Two tea...

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