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NASA discovers first Earth-sized planets outside solar system
Dec 21, 2011, 10:07 GMT
Washington - NASA's Kepler mission discovered the first two Earth-sized planets known to exist beyond the Earth's solar system, the US space agency announced Tuesday.
The discovery marks an important milestone in the search for planets similar to Earth, NASA said.
The new planets are thought to be rocky. Kepler-20e is slightly smaller than Venus and measures 0.87 times the radius of Earth. Kepler-20f is measuring 1.03 times Earth's radius. Both planets reside in a five-planet system called Kepler-20, approximately 1,000 light-years away in the constellation Lyra.
the planets are outside of what scientists refer to as the 'habitable zone' - the area around a star where liquid water could exist on a planet's surface and potentially support life.
Kepler-20e orbits its parent star every 6.1 days, and Kepler-20f every 19.6 days. Such short orbital periods mean very hot, inhospitable worlds, NASA said.
'Kepler-20f, at 800 degrees Fahrenheit, is similar to an average day on the planet Mercury,' NASA said. 'The surface temperature of Kepler-20e, at more than 1,400 degrees Fahrenheit, would melt glass.'
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