NASA's Kepler spacecraft has detected the tiniest world ever found around another star that's about as warm and luminous as the sun. The wimpy world (main image, artist's conception) is one of three planets (inset) orbiting Kepler 37, a star 220 light-years from Earth. As astronomers report online today in Nature, the diminutive world is only 3900 kilometers across—smaller than Mercury, only 10% larger than the moon, and 60% larger than Pluto. The puny planet is about as little as one found in 1993 circling a pulsar that also has three planets. In both solar systems, the smallest of the three worlds is the one nearest the star, just as Mercury is smaller and closer-in than Venus and Earth. Because we live on a rather small planet ourselves, the ability to discern such little worlds means astronomers may be approaching the day when they glimpse another life-bearing planet like our own.
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