Kepler-11g
Encyclopedia
Kepler-11g is an exoplanet
discovered in the orbit of the sunlike star Kepler-11
by the Kepler spacecraft, a NASA
satellite that is tasked with searching for terrestrial planet
s. Kepler-11g is the outermost of the six planets orbiting the star. The planet orbits at a distance that is nearly half of the mean distance between the Earth and the Sun
. It completes an orbit every 118 days, placing it at a distance that is much further from its host star than the system's inner five planets. It is estimated to have a radius that is four times larger than Earth
's, i.e. about Neptune's size. Kepler-11g's distance from the inner planets made its confirmation more difficult than that of the inner planets, as scientists had to work to exhaustively disprove all reasonable alternatives before Kepler-11g could be confirmed. The planet's discovery, along with that of the other Kepler-11 planets, was announced on February 2, 2011. According to NASA, the Kepler-11 planets form the flattest and most compact system yet discovered.
-157 when NASA
's Kepler spacecraft flagged the star for possible transit events, which exhibit tiny and roughly periodic decreases in the star's brightness are measured as it passes in front of its star as seen from Earth. Kepler-11's name is incorporated into Kepler-11g's name because it is the host star. As Kepler-11g and its five sister planets were discovered and announced at the same time, its planets were sorted alphabetically by distance from the host star, starting with the letter b. Because Kepler-11g was the furthest of the six, it was given the designation "g."
The Kepler team's scientists conducted follow-up observations to confirm or reject the planetary nature of the detected object. To do so, the scientists used the Keck 1 telescope at the W.M. Keck Observatory in Hawaii; the Shane
and Hale
telescopes in California; telescopes at the WIYN
(including the MMT
) and Whipple
observatories in Arizona; the Nordic Optical Telescope
in the Canary Islands; the Hobby-Eberly
and Harlan J. Smith
telescopes in Texas; and NASA's space-based Spitzer Space Telescope
. Because Kepler-11g orbits its star at a far greater distance than the inner five planets do, fewer transit events were observed, and radial velocity
(the observation of a Doppler effect
) interactions could not be easily discerned. As with the discovery of Kepler-9d
, the Kepler team ran the information through numerous models to see if Kepler-11g's light curve could fit the profile of some other object, including that of an eclipsing binary star in the background that may have contaminated the data. The probability that Kepler-11g is not a planet but instead a false positive was determined to be 0.18%, effectively confirming its existence.
Kepler-11g, along with its five sister planets, were announced at a NASA press conference on February 2, 2011. The findings were published in the journal Nature
a day later.
constellation. It is located approximately 613 parsec
s away. Kepler-11 is .95 (± 0.1) times the mass
and 1.1 (± 0.1) times the radius of the Sun. The star has an iron content (metallicity
) of 0 (± 0.1), similar to that of the Sun. Metallicity plays a vital role in the formation of planets, as a more metal-rich star tends to form more dense planets. Kepler-11 has an effective temperature
of 5680 (± 100) K, only slightly cooler than the Sun (5778 K). Kepler-11 hosts six known planets: Kepler-11b
, Kepler-11c
, Kepler-11d
, Kepler-11e
, and Kepler-11f
, all of which form a tight group well within the orbit of Mercury
. Kepler-11g is considerably farther away from Kepler-11 than its five sister planets. According to NASA, the planets orbiting Kepler-11 form the flattest and most compact system known.
Kepler-11 has an apparent magnitude
of 14.2, and thus cannot be seen with the naked eye
.
of Jupiter
, or 300 times the mass
of Earth. Its exact mass cannot be determined because while gravitational interactions of Kepler-11's five inner planets were used to determine their masses, Kepler-11g's comparatively large distance prevented it from affecting, or being affected by, the other five planets. As a result, only an upper limit can be placed on the mass, which is based on the assumption that if it were above this limit, gravitational effects on the other planets would be observed. Its radius is estimated to be 3.66 times that of Earth
, about Neptune's size. Kepler-11g has an estimated surface equilibrium temperature of 400 K, over 1.5 times that of Earth's equilibrium temperature. Kepler-11g orbits Kepler-11 every 118.37774 days (over 2.5 times that of the fifth planet from Kepler-11, Kepler-11f) at a distance of .462 AU
, almost half of the distance from which Earth orbits the Sun. Its eccentricity
is unknown. In comparison, planet Mercury
orbits the Sun every 87.97 days at a distance of .387 AU. With an orbital inclination
of 89.8°, Kepler-11g is seen almost edge-on with respect to Earth.
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
discovered in the orbit of the sunlike star Kepler-11
Kepler-11
Kepler-11 is a sun-like star slightly larger than the Sun in the constellation Cygnus, located some 2,000 light years from Earth. It is located within the field of vision of the Kepler spacecraft, the satellite that NASA's Kepler Mission uses to detect planets that may be transiting their stars...
by the Kepler spacecraft, a NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
satellite that is tasked with searching for terrestrial planet
Terrestrial planet
A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets are the inner planets closest to the Sun...
s. Kepler-11g is the outermost of the six planets orbiting the star. The planet orbits at a distance that is nearly half of the mean distance between the Earth and the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. It completes an orbit every 118 days, placing it at a distance that is much further from its host star than the system's inner five planets. It is estimated to have a radius that is four times larger than Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's, i.e. about Neptune's size. Kepler-11g's distance from the inner planets made its confirmation more difficult than that of the inner planets, as scientists had to work to exhaustively disprove all reasonable alternatives before Kepler-11g could be confirmed. The planet's discovery, along with that of the other Kepler-11 planets, was announced on February 2, 2011. According to NASA, the Kepler-11 planets form the flattest and most compact system yet discovered.
Name and discovery
Kepler-11 was originally called KOIKepler Object of Interest
A Kepler Object of Interest is a star observed by the Kepler spacecraft which is suspected of hosting one or more transiting planets. KOIs come from a master list of 150,000 stars which itself is generated from the Kepler Input Catalog . A KOI shows a periodic dimming, indicative of an unseen...
-157 when NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Kepler spacecraft flagged the star for possible transit events, which exhibit tiny and roughly periodic decreases in the star's brightness are measured as it passes in front of its star as seen from Earth. Kepler-11's name is incorporated into Kepler-11g's name because it is the host star. As Kepler-11g and its five sister planets were discovered and announced at the same time, its planets were sorted alphabetically by distance from the host star, starting with the letter b. Because Kepler-11g was the furthest of the six, it was given the designation "g."
The Kepler team's scientists conducted follow-up observations to confirm or reject the planetary nature of the detected object. To do so, the scientists used the Keck 1 telescope at the W.M. Keck Observatory in Hawaii; the Shane
C. Donald Shane telescope
The C. Donald Shane telescope is a reflecting telescope located at the Lick Observatory in California. It was named after astronomer C. Donald Shane in 1978, who led the effort to acquire the necessary funds from the California Legislature, and who then oversaw the telescope's construction...
and Hale
Hale telescope
The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning...
telescopes in California; telescopes at the WIYN
WIYN Observatory
The WIYN Observatory is owned and operated by the WIYN Consortium. Its telescope, a 3.5-meter instrument, is the newest and second largest telescope on Kitt Peak in Arizona...
(including the MMT
MMT Observatory
The MMT Observatory is an astronomical observatory on the site of Fred Lawrence Whipple Observatory . The Whipple observatory complex is located on Mount Hopkins, Arizona, USA in the Santa Rita Mountains...
) and Whipple
Fred Lawrence Whipple Observatory
The Fred Lawrence Whipple Observatory is an astronomical observatory owned and operated by the Smithsonian Astrophysical Observatory and is their largest field installation outside of their main site in Cambridge, MA...
observatories in Arizona; the Nordic Optical Telescope
Nordic Optical Telescope
The Nordic Optical Telescope is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. First light came in 1988, with regular observing beginning in 1989. It is funded by Denmark, Sweden, Iceland, Norway and Finland...
in the Canary Islands; the Hobby-Eberly
Hobby-Eberly Telescope
The Hobby-Eberly Telescope is a 9.2-meter aperture telescope located at the McDonald Observatory. It combines a number of features that differentiate it from most telescope designs, resulting in greatly lowered construction costs...
and Harlan J. Smith
Harlan J. Smith Telescope
The Harlan J. Smith Telescope is a 2.7m telescope located at the McDonald Observatory, in Texas, in the United States. This telescope is one of several research telescopes that are part of the University of Texas at Austin observatory perched atop Mount Locke in the Davis Mountains of west Texas...
telescopes in Texas; and NASA's space-based Spitzer Space Telescope
Spitzer Space Telescope
The Spitzer Space Telescope , formerly the Space Infrared Telescope Facility is an infrared space observatory launched in 2003...
. Because Kepler-11g orbits its star at a far greater distance than the inner five planets do, fewer transit events were observed, and radial velocity
Radial velocity
Radial velocity is the velocity of an object in the direction of the line of sight . In astronomy, radial velocity most commonly refers to the spectroscopic radial velocity...
(the observation of a Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
) interactions could not be easily discerned. As with the discovery of Kepler-9d
Kepler-9d
Kepler-9d, formerly known as KOI-377.03, is a planet in orbit around the sunlike star Kepler-9. Initially discovered by Kepler spacecraft, a terrestrial planet-searching satellite built and operated by NASA, Kepler-9d is most likely a Super-Earth, with an estimated radius approximately 60% larger...
, the Kepler team ran the information through numerous models to see if Kepler-11g's light curve could fit the profile of some other object, including that of an eclipsing binary star in the background that may have contaminated the data. The probability that Kepler-11g is not a planet but instead a false positive was determined to be 0.18%, effectively confirming its existence.
Kepler-11g, along with its five sister planets, were announced at a NASA press conference on February 2, 2011. The findings were published in the journal Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...
a day later.
Host star
Kepler-11 is a G-type star in the CygnusCygnus (constellation)
Cygnus is a northern constellation lying on the plane of the Milky Way. Its name is the Latinized Hellenic word for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross...
constellation. It is located approximately 613 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s away. Kepler-11 is .95 (± 0.1) times the mass
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
and 1.1 (± 0.1) times the radius of the Sun. The star has an iron content (metallicity
Metallicity
In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium...
) of 0 (± 0.1), similar to that of the Sun. Metallicity plays a vital role in the formation of planets, as a more metal-rich star tends to form more dense planets. Kepler-11 has an effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...
of 5680 (± 100) K, only slightly cooler than the Sun (5778 K). Kepler-11 hosts six known planets: Kepler-11b
Kepler-11b
Kepler-11b is an exoplanet discovered in the orbit of the star Kepler-11 by the Kepler spacecraft, a NASA-led mission to discover Earth-like planets. Kepler-11b is four times more massive and twice as large as Earth, but it has a lighter density estimated at a little over half Earth's, and is...
, Kepler-11c
Kepler-11c
Kepler-11c is an exoplanet discovered in the orbit of the sun-like star Kepler-11 by the Kepler spacecraft, a NASA telescope aiming to discover Earth-like planets. It is the second planet from its parent star, and is most likely a water planet with a thin hydrogen–helium atmosphere. Kepler-11c...
, Kepler-11d
Kepler-11d
Kepler-11d is an exoplanet discovered in the orbit of the sun-like 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...
, Kepler-11e
Kepler-11e
Kepler-11e is an exoplanet discovered in the orbit of the sunlike star Kepler-11. It is the fourth of six planets around Kepler-11 discovered by NASA's Kepler spacecraft. Kepler-11e was found by using the transit method, in which a the dimming effect that a planet causes as it crosses in front of...
, and Kepler-11f
Kepler-11f
Kepler-11f is an exoplanet discovered in the orbit of the sunlike star Kepler-11 by NASA's Kepler spacecraft, which searches for planets that transit their host stars. Kepler-11f is the sixth planet from its star, orbiting one fourth of the distance of the Earth from the Sun every 47 days...
, all of which form a tight group well within the orbit of Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
. Kepler-11g is considerably farther away from Kepler-11 than its five sister planets. According to NASA, the planets orbiting Kepler-11 form the flattest and most compact system known.
Kepler-11 has an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of 14.2, and thus cannot be seen with the naked eye
Naked eye
The naked eye is a figure of speech referring to human visual perception unaided by a magnifying or light-collecting optical device, such as a telescope or microscope. Vision corrected to normal acuity using corrective lenses is considered "naked"...
.
Characteristics
Kepler-11g, the sixth planet of six from its star, is estimated to be at most .95 times the massJupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, or 300 times the mass
Earth mass
Earth mass is the unit of mass equal to that of the Earth. 1 M⊕ = 5.9722 × 1024 kg. Earth mass is often used to describe masses of rocky terrestrial planets....
of Earth. Its exact mass cannot be determined because while gravitational interactions of Kepler-11's five inner planets were used to determine their masses, Kepler-11g's comparatively large distance prevented it from affecting, or being affected by, the other five planets. As a result, only an upper limit can be placed on the mass, which is based on the assumption that if it were above this limit, gravitational effects on the other planets would be observed. Its radius is estimated to be 3.66 times that of Earth
Earth radius
Because the Earth is not perfectly spherical, no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km...
, about Neptune's size. Kepler-11g has an estimated surface equilibrium temperature of 400 K, over 1.5 times that of Earth's equilibrium temperature. Kepler-11g orbits Kepler-11 every 118.37774 days (over 2.5 times that of the fifth planet from Kepler-11, Kepler-11f) at a distance of .462 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
, almost half of the distance from which Earth orbits the Sun. Its eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
is unknown. In comparison, planet Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
orbits the Sun every 87.97 days at a distance of .387 AU. With an orbital inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
of 89.8°, Kepler-11g is seen almost edge-on with respect to Earth.