Kepler-22 Exoplanet System

First-ever transiting exoplanet discovered in the habitable zone // Kepler-22, also known as KOI-87, is a real exoplanet system comprising a Sun-like star and one confirmed planet 635 light-years away in the constellation Cygnus. The host star is a yellow dwarf of spectral type G5V—slightly smaller and dimmer than the Sun but possibly more advanced in age at roughly 7 billion years. Kepler-22 weighs in at 0. 857 solar masses and 0. 869 solar radii with a surface temperature of 5596 K (5323 °C). It was among the first stars to be studied by the Kepler space telescope, just days after commencing its science operations back in 2009. Kepler-22 is the parent to one known exoplanet—Kepler-22 b. When its detection was published in 2011, it became the first-ever transiting exoplanet discovered in the habitable zone of a solitary star. Kepler-22 b follows a 290-day orbit at an average distance of 0. 812 AU. Assuming a low eccentricity, it would fit comfortably within the inner edge of Kepler-22's habitable zone and receive almost the same amount of energy as Earth does from the Sun. Its equilibrium temperature is estimated at ~279 K (6 °C), compared with Earth’s ~255 K (−18 °C), though actual surface conditions would depend on atmospheric greenhouse warming and internal heat sources. In terms of physical properties, Kepler-22 b has a radius of about 2. 1 Earth radii but with a poorly constrained mass, with only an upper limit of 9. 1 Earth masses known from radial velocity measurements. In any case, this places it above the regime of likely terrestrial planets, and it is generally considered more consistent with a volatile-rich world such as a water world or low-density mini-Neptune. Interior structure models suggest the planet could have a wide range of compositions, including substantial volatile fractions over 50% of its total mass. Some solutions allow for deep global oceans above high-pressure exotic ice mantles, though such scenarios are model-dependent rather than empirica