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Discovery of smallest planet yet a 'milestone' in search for another Earth

The Kepler space telescope has found a planet smaller than Mercury orbiting a distant star. The discovery suggests Kepler has the precision to find a planet more like Earth.


An artist's illustration compares the planets in the Kepler-37 system to the moon and planets in the solar system.


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For nearly 20 years, astronomers have filled the pantheon of planets beyond the solar system with objects ranging from behemoths several times Jupiter's mass to small orbs somewhat less hefty than Earth.

Now, a team reports finding the smallest planet yet – a true pipsqueak orbiting a sun-like star some 215 light-years away near the constellation Cygnus. The planet has a mass at least 1 percent of Earth's mass, probably more. And it's about 30 percent Earth's size. This is slightly larger than the moon, which is 27 percent the size of Earth.

The planet, one of three in the system, orbits its host star once every 13.4 days.


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