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Announcing Kepler 186-f: the First Earth-sized Exoplanet in the Habitable ZoneFor the past five years, the Kepler Space Telescope has allowed astronomers to observe over 3,800 potential exoplanets and confirm around 950 of them. Many of these planets have been discovered in what’s known as the goldilocks zone. This is an area around a host star where the conditions are right for liquid water to pool on a planet’s surface. Simply being in the habitable or goldilocks zone does not guarantee a planet will be habitable – the conditions have to be just right. Over the years, Kepler has spotted planets that were too hot or too large to truly be habitable. Today astronomers from NASA Ames and the SETI Institute have announced the discovery and validation of the first Earth-sized exoplanet orbiting its host star in the habitable zone. The host star, Kepler-186 is an older, dim red dwarf (or M dwarf) star. This system is home to five exoplanets, one of which could potentially have conditions ideal for life. The planet Kepler-186f, is on the outer edge of the habitable zone, orbiting its star once every 130 days and is approximately ten percent larger than Earth. The system is located approximately 500 light-years from Earth in the constellation Cygnus. Red dwarf stars are the most common stellar variety, with 7 out of every 10 stars in the Milky Way being M dwarf stars. Unlike our Sun, which is a yellow dwarf (G-type star), M dwarf stars are much cooler and dimmer. It is nearly impossible to determine the age of red dwarfs; however, their long life spans and cooler temperatures result in a closer habitable zone. M dwarf stars could very well be home to life beyond Earth. There are many characteristics of habitable planets aside from their location in the habitable zone – planet size and atmospheric conditions also play a role. Based on Kepler observations, astronomers have determined the size of Kepler-186f but not the composition or mass. Previous data indicates a planet the size of Kepler-186f would have a rocky composition similar to the Earth’s. Astronomers made this exciting discovery using the transitive method. The host star was observed and any dip in brightness would be indicative of another celestial body (such as a planet) crossing in front of it. Since Kepler-186f is only slightly larger than Earth and orbits fairly close to its star, we cannot directly observe it here on Earth. However with the upcoming Transiting Exoplanet Search Satellite (TESS) launching in 2017 and the James Webb Space Telescope (JWST) launching in 2018, we should soon be able to have a clearer picture of what Kepler-186f and other M dwarf planets are made of. -ALTImage & Source Credit: NASA/SETI Institute/JPL-Caltech

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