NASA's Kepler spots Earth-size planets outside our solar system

NASA space telescope Kepler spots smallest, but hot exoplanets ever confirmed around a star like our Sun.

nasa kepler
NASA's star-gazing telescope Kepler has added to its amazing discoveries list by spying the first Earth-size planets orbiting a Sun-like star outside our solar system.

NASA says while the planets are too close and too hot to the star to be in the so-called habitable zone where liquid water could exist , they are the smallest exoplanets ever confirmed around a star like our Sun.

Read more: The weirdest, wackiest and coolest sci/tech stories of 2011

The planets are thought to be rocky and one, dubbed Kepler-20e is slightly smaller than Venus, measuring 0.87 times the radius of Earth. Kepler-20e orbits its parent star every 6.1 days and Kepler-20f every 19.6 days. These short orbital periods mean very hot, inhospitable worlds. The surface temperature of Kepler-20e, at more than 1,400 degrees Fahrenheit (760 degrees Celsius), would melt glass.

The other, Kepler-20f is slightly larger than Earth, measuring 1.03 times its radius. Both planets reside in a five-planet system called Kepler-20, approximately 1,000 light-years away in the constellation Lyra, NASA stated.  Kepler-20f, at 800 degrees Fahrenheit (427 degrees Celsius), is similar to an average day on the planet Mercury.

NASA said the Kepler-20 system includes three other planets that are larger than Earth but smaller than Neptune. Kepler-20b, the closest planet, Kepler-20c, the third planet, and Kepler-20d, the fifth planet, orbit their star every 3.7, 10.9 and 77.6 days, respectively. All of the planets in the system have orbits lying roughly within Mercury's orbit in our solar system and the host star is slightly smaller and cooler than ours, NASA said. .

The findings are just the latest Kepler discovery.  NASA this month said it had confirmed finding the first planet in what's known as the  "habitable zone," located 600 light-years away from Earth.  Spotted by Kepler, the planet is the smallest yet found to orbit in the middle of the habitable zone -- the region in space where liquid water could exist on a planet's surface of a star similar to our sun.

 The planet, dubbed Kepler-22b is about 2.4 times the radius of Earth and an orbit of 290 days around a sun-like star resembles that of our world. The planet is orbiting the same class of star as our sun, called G-type, although it is slightly smaller and cooler, NASA stated.

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