Kepler-11e
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Kepler-11e is an
exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...
(extrasolar planet) discovered in the orbit of the sunlike star
Kepler-11 Kepler-11, also designated as 2MASS J19482762+4154328, is a Sun-like star slightly larger than the Sun in the constellation Cygnus, located some 2,110 light years from Earth. It is located within the field of vision of the Kepler spa ...
. It is the fourth of six planets around Kepler-11 discovered by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
's
Kepler space telescope The Kepler space telescope is a defunct space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orb ...
. Kepler-11e was found by using the
transit method Methods of detecting exoplanets usually rely on indirect strategies – that is, they do not directly image the planet but deduce its existence from another signal. Any planet is an extremely faint light source compared to its parent star. For e ...
, in which the dimming effect that a planet causes as it crosses in front of its star is measured. Kepler-11e is most likely a
gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" was originally synonymous with "giant planet". However, in the 1990s, it became known that Uranu ...
like
Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...
, having a density that is less than that of
Saturn Saturn is the sixth planet from the Sun and the second largest in the Solar System, after Jupiter. It is a gas giant, with an average radius of about 9 times that of Earth. It has an eighth the average density of Earth, but is over 95 tim ...
, the least dense planet in the Solar System. Its low density can probably be attributed to a large hydrogen and helium atmosphere. Kepler-11e has a mass eight times of Earth's mass and a radius 4.5 times that of Earth. The planet orbits its star every 31 days in an ellipse that would fit within the orbit of Mercury. Kepler-11e was announced on February 2, 2011 with its five sister planets after it was confirmed by several observatories.


Name and discovery

At the time when Kepler-11 was first noted as a host to a potential transit event, the star was given the designation KOI-157. It was later assigned the name "Kepler-11" after the Kepler spacecraft, a
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
satellite tasked with discovering planets in transit of, or crossing in front of, their stars. This transit causes a slight and regular change in the host star's brightness, which can then tested to prove the planet's existence and, later, to extrapolate the orbital parameters of the planet. Kepler-11e is first given the designation by its host star, Kepler-11. Since Kepler-11e was announced with five other planets, the letters added to the star are sorted by the planet's distance from its star. Kepler-11e is the fourth planet from Kepler-11, it is given the designation "e". Follow-up confirmation observations were made by the Keck 1 telescope at the W. M. Keck Observatory in Hawaii, the Hale and Shane telescopes in California, the Harlan J. Smith and Hobby–Eberly telescopes in west Texas, the
Nordic Optical Telescope The Nordic Optical Telescope (NOT) is an astronomical telescope located at Roque de los Muchachos Observatory, La Palma in the Canary Islands. The telescope saw first light in 1988, and was officially inaugurated during September 1989. Regular o ...
in the Canary Islands, and by telescopes at the WIYN (including MMT) and Whipple observatories in Arizona. The
Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003, that was deactivated when operations ended on 30 January 2020. Spitzer was the third space telescope dedicate ...
was also used. Kepler-11's planetary system became the first discovered extrasolar system with more than three transiting planets, as well as the most compact and flattest system yet discovered, according to NASA. The planets of Kepler-11, including Kepler-11e, were announced jointly at a press conference on February 2, 2011. The findings were published in the journal ''
Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...
'' on February 3.


Host star

Kepler-11 is a
G-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
located in the constellation of Cygnus. It has a mass of 0.95 Msun and a radius of 1.1 Rsun, and is thus almost the same mass and radius as the Sun. With an
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. Effective temperature is often used as an estimate of a body's surface temperature ...
of 5680 K, it is also almost as hot as the Sun, and with a
metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...
of 0, Kepler-11 is almost as metal-rich as the Sun is. Metal-rich stars tend to have easily detectable planets because higher metallicities tend to either facilitate the creation of gas giants or to promote
planetary migration Planetary migration occurs when a planet or other body in orbit around a star interacts with a disk of gas or planetesimals, resulting in the alteration of its orbital parameters, especially its semi-major axis. Planetary migration is the most ...
, in which the planet orbits more closely to its star. However, Kepler-11 is almost 1.73 times older than the Sun, as it has an estimated age of eight billion years. Kepler-11 is 613
parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (AU), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...
s away from the Earth; its distance contributes to its
apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
of 14.2 (V). It, thus, cannot be seen with the naked eye. Other than Kepler-11e, Kepler-11 is the host star of the planets Kepler-11b,
Kepler-11c Kepler-11c is an Extrasolar planet, exoplanet discovered in the orbit of the Sun-like star Kepler-11 by the Kepler space telescope, a NASA telescope aiming to discover Terrestrial planet, Earth-like planets. It is the second planet from its star, ...
, 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.


Characteristics

Kepler-11e, which formed within the first few million years of the star system's formation, 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 Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently pur ...
at
standard temperature and pressure Standard temperature and pressure (STP) or standard conditions for temperature and pressure are various standard sets of conditions for experimental measurements used to allow comparisons to be made between different sets of data. The most used ...
and slightly less than the density of Saturn. Kepler-11e has a surface
equilibrium temperature The planetary equilibrium temperature is a theoretical temperature that a planet would be if it were in radiative equilibrium, typically under the assumption that it radiates as a black body being heated only by its parent star. In this model, th ...
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. Kepler-11e's orbital
inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...
is 88.8°, making it almost entirely edge-on to its star as seen from Earth. Because it isn't as close to its star as its sister planets Kepler-11b and
Kepler-11c Kepler-11c is an Extrasolar planet, exoplanet discovered in the orbit of the Sun-like star Kepler-11 by the Kepler space telescope, a NASA telescope aiming to discover Terrestrial planet, Earth-like planets. It is the second planet from its star, ...
, 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 A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
. 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).


References

{{Kepler-11 Hot Neptunes Exoplanets with Kepler designations Exoplanets discovered in 2011 Transiting exoplanets Cygnus (constellation) 11e e