The lineup compares artist's concepts of the planets in the Kepler-37 system to the Moon and planets in the solar system. The smallest planet, Kepler-37b, is slightly larger than our Moon, measuring about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the third planet, is twice the size of Earth. // NASA/Ames/JPL-Caltech