Comparing Kepler-37 and Sol systems. Artwork comparing planets in our solar system and the Kepler-37 system. The Kepler-37 planets, detected in September 2012 by NASA's Kepler space observatory, are about 210 light years distant in the constellation Lyra. One of the planets (Kepler-37b) is the smallest yet found around a Sun-like star. It is slightly larger than our Moon, about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, almost three-quarters the size of Earth. Kepler-37d, the third planet (about 25,500 kilometres in diameter), is twice the size of Earth. All three planets orbit very close to their parent star.