page_title: Kepler-8b
section_title: Characteristics
hierarchical_section_title: Kepler-8b / Characteristics
caption_attribution_description: English: The size of Kepler's first five planet discoveries as compared with Jupiter and Earth in our own solar system. NASA's Kepler space telescope has discovered its first five new exoplanets, or planets beyond our solar system. Kepler's high sensitivity to both small and large planets enabled the discovery of the exoplanets, named Kepler 4b, 5b, 6b, 7b and 8b. The discoveries were announced Monday, Jan. 4, by the members of the Kepler science team during a news briefing at the American Astronomical Society meeting in Washington.
context_page_description: Kepler-8b is the fifth of the first five exoplanets discovered by NASA's Kepler spacecraft, which aims to discover planets in a region of the sky between the constellations Lyra and Cygnus that transit their host stars. The planet is the hottest of the five. Kepler-8b was the only planet discovered in Kepler-8's orbit, and is larger than Jupiter. It orbits its host star every 3.5 days. The planet also demonstrates the Rossiter–McLaughlin effect, where the planet's orbit affects the redshifting of the spectrum of the host star. Kepler-8b was announced to the public on January 4, 2010 at a conference in Washington, D.C. after radial velocity measurements conducted at the W.M. Keck Observatory confirmed its detection by Kepler.
context_section_description: Kepler-8b has a mass of .603 MJ, but a radius of 1.419 RJ. This means that although Kepler is approximately 60% the mass of planet Jupiter, it is more diffuse, as it is 41.9% wider. Based on its size and the distance from its star, Kepler-8b is a Hot Jupiter planet, orbiting Kepler-8 from a distance of .0483 AU every 3.52254 days. To compare, planet Mercury orbits the Sun at an average distance of .3871 AU every 87.97 days. With an equilibrium temperature of 1764 K, Kepler-8b was the hottest of the five planets announced during the conference stating its discovery. Kepler-8b has an eccentricity of 0, which means that its orbit is very circular. The planet also has a density of .261 grams/cc, approximately 74% less dense than purified water at 4 °C.
  As Kepler-8b orbits its star, it demonstrates the Rossiter–McLaughlin effect, in which the host star's spectrum becomes red- and, later, blueshifted, as a body transits it. The identification of this effect established Kepler-8b as orbiting in a prograde motion (as opposed to retrograde motion, in which a planet orbits in a direction opposite of its star's rotation). The study in 2012, have determined the planetary orbit is probably well aligned with the equatorial plane of the star, misalignment equal to 5±7°.
  The planet is likely to be tidally locked to the parent star. In 2015, the planetary nightside temperature was estimated to be equal to 1859±227 K.
caption: The first five planets discovered by Kepler, compared by relative size. Kepler-8b is depicted in orange.
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