Kepler-296e (also known by its Kepler Object of Interest designation KOI-1422.05) is a confirmed super-Earth exoplanet orbiting within the habitable zone of Kepler-296. The planet was discovered by NASA's Kepler spacecraft using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. NASA announced the discovery of the exoplanet on 26 February 2014.[1]
Characteristics
Kepler-296e was assumed to be a super-Earth with a radius 1.75 times that of Earth. A more revised estimate puts the planet at 1.53 Earth-radii. The planet orbits Kepler-296 once every 34.1 days at a semimajor axis distance of 0.169 AU.[4] It would have a mass of 4.52 Earth masses, with the higher-than-Earth density suggested by exoplanetkyoto.[5] With an Earth-like density, the mass would be 3.58 Earth masses. The planet's equilibrium temperature is 267 K (–6 °C; 21 °F), much higher than that of Earth.
The planet was announced as being located within the habitable zone of Kepler-296. In this region, liquid water could exist on the surface of the planet.[6] It is likely rocky, with its relatively low radius, in contrast to f, which is larger.[4][6] As of 2017, with an ESI of 0.85, it is the fifth-most Earth-like planet after Kepler-438b, TRAPPIST-1 d, and two Gliese-designated planets, GJ 3323 b and Gliese 273 b (Luyten b) which were both discovered in 2017.[7] The planet receives 1.4 times the Earth's solar flux, putting it well within the habitable zone and just barely beyond the runaway G line.[7][8] According to Kopparapu et. al (2013), the planet is within the most conservative boundaries of the habitable zone.[9] However, it has an eccentric orbit,[4][10] with a maximum eccentricity of 0.33 to a confidence of 3-sigma.[4] The planet's equilibrium temperature varies depending on its albedo: for a non-tidally locked planet with an Earth-like albedo of 0.3, it is 234 K (–39 °C; –38 °F), and for a Venus-like albedo of 0.7, it is 189 K (–84 °C; -119 °F). For a tidally locked planet with an Earth-like albedo of 0.3, the equilibrium temperature is 278 K (5 °C; 41 °F).[5]
Tidal locking
According to,[11] an Earth-size planet with eccentricity <0.1, no moons, and no obliquity orbiting at the Earth boundary within the habitable zone is tidally locked around a star with a mass of <0.42 solar masses (~M2 or later). When the Solar System is used as a yardstick, then the limit is 0.72 solar masses (~K3-4 or later). However, the orbit of planet e, is likely more eccentric than the modeled fictional planet, so the planet may not have had enough time to tidally lock.[4][10]
