NASA's Kepler spacecraft, a space observatory in orbit around the Sun, has confirmed the discovery of an extrasolar planet, orbiting in the "habitable zone", the region around a star where an Earth-like planet can maintain liquid water on its surface. (Planets circling other stars are termed extrasolar planets or exoplanets. As of early December 2011, over 700 extrasolar planets have been discovered.) Kepler also has discovered over 1,000 new exoplanet candidates, nearly doubling its previous record. Ten of these candidates are about the size of Earth, and orbit in the habitable zone of their parent star. Candidates require follow-up observations to verify their planetary nature.
The newly confirmed planet, technically designated Kepler-22b, is the smallest yet found to orbit in the middle of the habitable zone of a Sun-like star. Kepler-22b is about 2.4 times the radius of Earth. Scientists haven't yet determined Kepler-22b’s composition, but its discovery is a step closer to identifying Earth-like exoplanets.
Previous research indicated the existence of Earth-size planets in habitable zones, but clear confirmation remained difficult. Two other small planets orbiting stars smaller and cooler than our Sun were recently confirmed on the borders of the habitable zone, with orbits similar to those of Venus and Mars.
When an exoplanet passes in front of its star, it gives rise to a tiny drop in star’s brightness. Kepler discovers exoplanets by detecting these brightness dips. Kepler performs at least three confirmatory observations, to verify an exoplanet’s discovery.
Kepler-22b is located 600 light-years away. While this planet is larger than Earth in size, its 290-days orbit around a Sun-like star resembles that of Earth. Kepler-22b's star belongs to the same stellar class as our Sun, called G-stars, although it is slightly smaller and cooler.
The Kepler observatory was launched into space in March 2009. It is named in honor of the 17th century German astronomer Johannes Kepler, who discovered the laws of planetary motion. Kepler observatory constantly monitors the brightness of nearly 150,000 stars, located within a fixed field of view. Its prime mission is to discover Earth-size planets in, or near the habitable zone.
References
NASA
www.nasa.gov/
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