Kepler 186f is an exoplanet orbiting the red dwarf named Kepler-186, about 500 light years away from Earth. It is the first exoplanet with a radius similar to Earth's to be discovered to be in the habitable-zone (also known as Goldilocks zone) of another star. The planet is about 11% larger in radius than Earth (between 4.5% smaller and 26.5% larger), giving a volume about 1.37 times that of Earth (between 0.87 and 2.03 times as large). The estimated equilibrium temperature for Kepler-186f, which is the surface temperature without an atmosphere, is said to be around 188 K (−85 °C; −121 °F), somewhat colder than the equilibrium temperature of Mars.
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The planet orbits a (M-type) star named Kepler-186, orbited by a total of five planets. The star has a mass of 0.54 M and a radius of 0.52 R. It has a temperature of 4017 K and is about 4 billion years old, about 600 million years younger than the Sun, which is 4.6 billion years old and has a temperature of 5778 K. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.62. Therefore, it is too dim to be seen with the naked eye. On the Earth-like planet, the sunsets are very similar. Since the star is a red dwarf, the sunsets are a more, red blood like colour, as to our sunsets are orange and yellow likea flame.
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The image on the right is not a real image from the planet, but an illustration image to compare sunsets with out Earth and Kepler 186f. Kepler-186f orbits its star with about 4% of the Sun's luminosity with an orbital period of 129.9 days and an orbital radius of about 0.40 times that of Earth's (compared to 0.39 AU for Mercury). The habitable zone for this system is estimated conservatively to extend over distances receiving from 88% to 25% of Earth's illumination (from 0.23 to 0.46 AU). Kepler-186f receives about 32%, placing it within the conservative zone but near the outer edge, similar to the position of Mars in our Solar System.
Even if the planet is in the habitable-zone, it's not ensured to be habitable. It's atmospheres characteristics are unknown, which makes scientists and researchers unsure if t can be habitable. But for one, it is too distant from it's parent star to be habitable, almost like Mars. The host star has four other planets discovered, 186 a,b,c,d and e. But all of them are too close to their star, making it too hot for liquid water. The four innermost planets are probably tidally locked, but Kepler-186f is in a higher orbit, where the star's tidal effects are much weaker, so the time could have been insufficient for its spin to slow down significantly. Because of the very slow evolution of red dwarfs, the age of the Kepler-186 system was poorly constrained, although it is likely to be greater than a few billion years. Recent results have placed the age at around 4 billion years.[3] The chance that it is tidally locked is approximately 50%. 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.
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At nearly 560 light-years (171 pc) distant, Kepler-186f is too far and its star too faint for current telescopes or the next generation of planned telescopes to determine its mass or whether it has an atmosphere. However, the discovery of Kepler-186f demonstrates conclusively that there are other Earth-sized planets in habitable zones. The Kepler spacecraft focused on a single small region of the sky but next-generation planet-hunting space telescopes, such as TESS and CHEOPS, will examine nearby stars throughout the sky.
