Kepler-11

Kepler-11b is an exoplanet orbiting around the star Kepler-11 by the Kepler space telescope, a NASA-led mission to discover Earth-like planets. Kepler-11b is a super-Earth, but less than about three times as massive and twice as large as Earth, but it has a lower density (≤ 3 g/cm³), and is thus most likely not of Earth-like composition. Kepler-11b is the hottest of the six planets in the Kepler-11 system, and orbits more closely to Kepler-11 than the other planets in the system. Kepler-11b, along with its five counterparts, form the first discovered planetary system with more than three trans…

Naming and discovery

Kepler-11b is named in two parts. The first part of its name is derived from the fact that it orbits the star Kepler-11. As the discovery of Kepler-11b was announced simultaneously with those of other planets, Kepler-11b was given the designation b because it was the innermost of the six announced planets. The host star, Kepler-11, was named for the Kepler Mission that flagged it as host to several potential transit events under the name KOI-157. The Kepler satellite is a NASA-run space telescope that is tasked with the discovery of terrestrial planets that transit, or cross in front of, their…

Ground-based telescopes in California, Hawaii, the Canary Islands, Arizona, and Texas, as well as the Spitzer Space Telescope, were used to conduct these follow-up observations and verify Kepler-11b's existence. In particular, the detection of an orbital resonance effect between Kepler-11b and Kepler-11c confirmed the find. Kepler-11b's discovery was announced to the public on February 2, 2011. It is part of the first system discovered with more than three transiting planets, and is also part of the most compact and flat system yet discovered. Kepler-11's planetary system is the second known s…

Host star

Kepler-11 is a star in the constellation Cygnus that has a mass of 0.95 (± 0.1) Msun and a radius of 1.1 (± 0.1) Rsun. In other words, Kepler-11 is approximately 5% less massive and 10% wider than the Sun. The star's metallicity is 0 (± 0.1), meaning that the level of iron (and, presumably, other elements) in the star is almost the same as that of the Sun. Metallicity plays an important role in planetary systems, and stars with higher metallicity are more likely to have planets detected around them. This may be because the higher metallicity provides more material with which to quickly build p…

Kepler-11 has an apparent magnitude of 14.2. It is too dim to see from Earth with the naked eye.

Characteristics

Kepler-11b is estimated to be 2.78+0.64 −0.66 Earth masses and 1.8 Earth radii, making it around three times (or less) as massive and nearly twice as large as Earth. The mass is determined using transit timing variations of Kepler-11c, and is limited by the quality of the data. Kepler-11b is the closest planet to its host star in the Kepler-11 planetary system. With an estimated density of 4.5 g/cm³, less than Venus's, Kepler-11b is denser than the solar system's gas giants but slightly less dense than the terrestrial planets. Early estimates have suggested that it is not of Earth-like composi…

Atmosphere

Kepler-11b close proximity to the star implies a strong insolation, which caused the planet to lose all of light-element envelope acquired during formation. The observed low density does require the presence of a gaseous envelope though, which was most likely produced via outgassing of hydrogen or evaporation of H₂O from the condensed core. The mass of atmosphere of Kepler-11b is not strongly constrained by observations, and may represent 0.04±0.03% of planetary mass - close to such value of Venus. For comparison, atmosphere mass ratio of Earth is 0.00008%.

Orbit

Kepler-11b and Kepler-11c orbit Kepler-11 with a strong orbital resonance, which gravitationally tugs the planets into stable orbits at a set ratio. The ratio of the resonance between Kepler-11b and c is 5:4. Kepler-11b's orbit is in a regime where secular resonance may abruptly destabilize its orbit; if this were to happen, it would most likely collide with c.

Kepler-11c is an exoplanet orbiting around the star Kepler-11 by the Kepler space telescope, a NASA telescope aiming to discover Earth-like planets. It is the second planet from its star, and is most likely a water planet with a thin hydrogen–helium atmosphere. Kepler-11c orbits Kepler-11 every 10 days, and has an estimated density twice that of pure water. It is estimated to have a mass thirteen times that of Earth and a radius three times that of Earth. Kepler-11c and its five sister planets form the first discovered system with more than three transiting planets. The Kepler-11 system also h…

Name and discovery

Kepler-11c's name is divided into two parts: it is named for Kepler-11, the star around which it orbits. As planets with discoveries that are announced at the same time are sorted by distance, Kepler-11c's "c" is because it was the second-closest planet from its host star at the time of discovery (Kepler-11b is the closest). Kepler-11, the host star, was named for the Kepler satellite, a NASA telescope that searches for terrestrial planets by measuring small fluctuations in the light of stars that occurs when celestial bodies transit, or cross in front of, the star with respect to Earth. Keple…

Follow-up observations were conducted by the Hale and the C. Donald Shane telescopes in California; MMT, WIYN, and Tillinghast telescopes in Arizona; the Keck I telescope in Hawaii; the Hobby–Eberly and Smith telescopes in Texas; and the Nordic Optical Telescope in the Canary Islands.

Host star

Kepler-11 is a star 2,000 light-years away in the constellation Cygnus. With a mass of .95 Msun, a radius of 1.1 Rsun, a metallicity of [Fe/H] = 0, and an effective temperature of 5680 (± 100) K, Kepler-11 is almost identical to the Sun in terms of radius, mass, and temperature. However, Kepler-11 is much older than the Sun, with an estimated age of 8 (± 2) billion years (the Sun is approximately 4.6 billion years old). Along with Kepler-11c, Kepler-11 is host to the planets Kepler-11b, Kepler-11d, Kepler-11e, Kepler-11f, and Kepler-11g. The inner five planets' orbits would fit within the orbi…

With an apparent magnitude of 14.2, Kepler-11 cannot be seen from Earth with the naked eye.

Characteristics

Kepler-11c has a mass of 13.5 ME and a radius of 3.15 RE, making it over 13.5 times the mass of earth, but approximately 3.15 times its radius. Neptune, in comparison, has a radius approximately 3.9 times that of Earth. With a density of 2.3 grams/cm³, Kepler-11c has a mass over double of that of pure water at 0 °C; it is also denser than all the Sun's gas giants, but less dense than any of its rocky planets. Its density is closest to the dwarf planet Pluto. Due in part to its proximity to its star, the planet's equilibrium temperature is 833 K, about three times hotter than Earth's average te…

The Kepler team has said that Kepler-11b and Kepler-11c are probably composed mostly of water with a thin hydrogen and helium atmosphere. In comparison to the outer planets of the system, which probably have large hydrogen and helium atmospheres, Kepler-11c's proximity to its star has blown off most of its atmosphere. In fact, formation and evolution calculations indicate that Kepler-11c lost over 50% (by mass) of the hydrogen envelope it had accreted after formation. Support to the idea that the planets of this system formed ex situ and contain large amounts of H₂O is provided by the radius o…

Kepler-11 and its six-planet system form what NASA considers to be the most compact and flattest planetary system yet discovered. Kepler-11b and Kepler-11c orbit Kepler-11 with a phenomenon called orbital resonance, a gravitational tugging that keeps their orbits stable at a ratio of the orbital periods close to 5:4 . Orbital resonances can arise from orbital migration during formation. Kepler-11c may be at risk of eventually colliding with b due to a precarious orbital configuration in which a secular resonance could emerge and cause planet b's orbit to become dangerously eccentric.

Kepler-11d is an exoplanet orbiting around the star Kepler-11. It is named for the telescope that discovered it, a NASA spacecraft named Kepler that is designed to detect Earth-like planets by measuring small dips in the brightness of their host stars as the planets cross in front. This process, known as the transit method, was used to note the presence of six planets in orbit around Kepler-11, of which Kepler-11d is the third from its star. Kepler-11d orbits Kepler-11 well within the orbit of Mercury approximately every 23 days. The planet is approximately six times more massive than the Eart…

Name and discovery

As with all exoplanets, Kepler-11d is named first for its host star, Kepler-11. Because Kepler-11d was announced at the same time as the five other planets in the system, their names are sorted by their distances from the host star; thus, because Kepler-11d is the third planet from Kepler-11, it was given the designation d. Kepler-11 was named for the Kepler space telescope, a NASA Earth-trailing satellite purposed with discovering Earth-like planets in a small area of the sky between the constellations Cygnus and Lyra by observing planets that transit, or cross in front of, their host stars w…

Required follow-up observations were conducted at the Hale and Shane telescopes in California; the W. M. Keck Observatory's Keck I telescope in Hawaii; telescopes at the WIYN, Whipple, and MMT observatories in Arizona; and the Hobby–Eberly and Harlan J. Smith telescopes of west Texas. Additionally, the Spitzer Space Telescope was used. Kepler-11d, along with its five sister planets, were announced to the public on February 2, 2011. Its discovery paper was published in the journal Nature the next day.

Host star

Kepler-11 is a star in the constellation Cygnus. With a mass of .95 Msun, a radius of 1.1 Rsun, a measured metallicity of 0, and an effective temperature of 5680 K, Kepler-11 is near in mass (95% of Sun), radius (110% of Sun), and iron content as the Sun. Metallicity has been observed to play a major role determining the type of planet a star forms. As metal-rich gas clouds tend to cause planetary cores to aggregate to a gravitationally prominent size while primordial gases still exist in the system, gas giants tend to form under such conditions. It is also slightly cooler than the Sun. Howeve…

At a distance of approximately 659 parsecs,

Characteristics

Kepler-11d has a mass of 6.1 ME and a radius of 3.43 RE, making it some six times more massive than Earth with nearly three and a half times the radius. With a density of .9 grams/cm³, Kepler-11d's density is less than that of water and comparable to that of the gas giant Saturn. This suggests that, unlike its sister planets Kepler-11b and Kepler-11c, which are closer to their host star, Kepler-11d has maintained a large (in volume) atmosphere that is most likely composed of hydrogen and helium. Nonetheless, formation models indicate that most of the mass is accounted for by heavy elements and…

The presence of large quantities of hydrogen and helium on Kepler-11d, Kepler-11e, and Kepler-11f suggests that these planets formed within the first few million years of the system's existence, when gas could still be captured from the forming protoplanetary disc. In fact, according to detailed formation calculations, all planets of the system require some amount of hydrogen/helium in order to match their observed radii. The innermost planet, Kepler-11b, which likely lost all of its primordial light-element envelope, still requires a tenuous atmosphere (either made of steam or of gases seques…