Kepler-22b, seen in this artist's rendering, is a planet a bit larger than Earth that orbits in the habitable zone of its star. Some researchers think there might be "superhabitable" worlds that may not resemble Earth. NASA/Ames/JPL-Caltech hide caption

itoggle caption NASA/Ames/JPL-Caltech

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

An illustration shows how the planet Kepler-36c might look from the surface of the neighboring Kepler-36b. David Aguilar/Harvard-Smithsonian Center for Astrophysics/NASA hide caption

itoggle caption David Aguilar/Harvard-Smithsonian Center for Astrophysics/NASA

Circa 1612, German astronomer Johannes Kepler (1571 - 1630) Hulton Archive/Getty Images hide caption

itoggle caption Hulton Archive/Getty Images