Kepler-11e

Kepler-11 is a G-type star^[4] located in the constellation of Cygnus. It has a mass of 0.95 M_sun and a radius of 1.1 R_sun, and is thus almost the same mass and radius as the Sun. With an effective temperature of 5680 K, it is also almost as hot as the Sun, and with a metallicity of 0, Kepler-11 is almost as metal-rich as the Sun is. Metal-rich stars tend to have easily detectable planets^[7] because higher metallicities tend to either facilitate the creation of gas giants or to promote planetary migration, in which the planet orbits more closely to its star.^[8] However, Kepler-11 is almost 1.73 times older than the Sun, as it has an estimated age of eight billion years.^[2] Kepler-11 is 613 parsecs away from the Earth; its distance contributes to its apparent magnitude of 14.2 (V). It, thus, cannot be seen with the naked eye.^[2] Other than Kepler-11e, Kepler-11 is the host star of the planets Kepler-11b, Kepler-11c, Kepler-11d, Kepler-11f, and Kepler-11g. The inner five planets in the system orbit in a tightly knit configuration that would fit within the orbit of planet Mercury, while Kepler-11g, compared to its inner sister planets, orbits at a much further distance.^[1]

Kepler-11e, which formed within the first few million years of the star system's formation,^[9] has a mass 8.4 times that of Earth's, and radius 4.52 times that of Earth's. With a density of 0.5 grams/cm³, Kepler-11e has a density that is half of that of pure water at standard temperature and pressure and slightly less than the density of Saturn.^[5] Kepler-11e has a surface equilibrium temperature of 617 K, and is thus has an equilibrium temperature approximately 2.4 times hotter than Earth's. Kepler-11e orbits its star at a mean distance of .194 AU, making it the fourth planet from its star. It completes an orbit every 31.995990 days. In comparison, Mercury orbits the Sun every 87.97 days at a distance of 0.387 AU.^[10] Kepler-11e's orbital inclination is 88.8°, making it almost entirely edge-on to its star as seen from Earth.^[2]

Because it isn't as close to its star as its sister planets Kepler-11b and Kepler-11c, the Kepler team suggests that its light density may come from a large hydrogen and helium atmosphere that has not been blown away by the stellar wind.^[1] In fact, formation models indicate that the planet has a gaseous envelope, somewhat less massive than 20% of it total mass, which account for ≈60% of its radius (or ≈90% of its volume).^[11]