Planets similar to Earth
Kepler-186f is an exoplanet orbiting the red dwarf Kepler-186, about 500 light-years from the Earth. It is the first planet with a radius similar to Earth's to be discovered in the habitable zone of another star. NASA'sKepler spacecraft detected it using the transit method, along with four additional planets orbiting much closer to the star (all modestly larger than Earth). Analysis of three years of data was required to find its signal. The results were presented initially at a conference on 19 March 2014[8] and some details were reported in the media at the time. The full public announcement was on 17 April 2014, followed by publication in Science
The star hosts four other planets discovered so far, though Kepler-186 b, c, d, and e (in order of increasing orbital radius) are too close to the star, and so too hot, to have liquid water. The four innermost planets are probably tidally locked but Kepler-186f is further out, where the star's tidal effects are much weaker, so there may not have been enough time for its spin to slow down that much. Because of the very slow evolution of red dwarfs, the age of the Kepler-186 system is poorly constrained, although it is likely to be greater than a few billion years. There is a roughly 50-50 chance it is tidally locked. Since it is closer to its star than Earth is to the Sun, it will probably rotate much more slowly than Earth; its day could be weeks or months long (see Tidal effects on rotation rate, axial tilt and orbit).