An artist's rendering of Kepler-186f, the first validated Earth-size planet to orbit in the habitable zone of a distant star. T. Pyle/NASA/SETI Institute/JPL-Caltech hide caption

itoggle caption T. Pyle/NASA/SETI Institute/JPL-Caltech

An artist's illustration of Kepler-22b, a planet that circles its star in the "goldilocks" zone. Ames/JPL-Caltech/NASA/Getty Images hide caption

itoggle caption Ames/JPL-Caltech/NASA/Getty Images

This illustration shows the relative sizes of the habitable-zone planets Kepler-22b, Kepler-69c, Kepler-62e, Kepler-62f and the Earth. NASA/Ames/JPL-Caltech hide caption

itoggle caption NASA/Ames/JPL-Caltech

A NASA illustration comparing the newly discovered planets to Venus and Earth. Kepler-20e is slightly smaller than both Venus and Earth. Kepler-20f is slightly larger. NASA/Ames/JPL-Caltech hide caption

itoggle caption NASA/Ames/JPL-Caltech