Kepler-11
Encyclopedia
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. Announced on February 2, 2011, the star system is the most compact yet discovered and is the flattest known. It is the first discovered case of a star system with six transiting planets. All discovered planets are larger than Earth, with the larger ones being about Neptune's size.
's Kepler Mission
, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from the perspective of Earth
. Kepler-11 is the first discovered exoplanetary system with more than three transiting planets.
Kepler-11 is named for the Kepler Mission: it is the 11th star with confirmed planets discovered by Kepler.
The planets are named alphabetically, starting with the innermost: b, c, d, e, f, and g, distinguishers that are tagged onto the name of their home star.
. It has a surface temperature of 5680 (± 100) K and is 8 (± 2) billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K.
The star's apparent magnitude
, or how bright it appears from Earth's perspective, is 13.7. Therefore, it cannot be seen with the naked eye.
the star; this means that all six planets' orbits appear to cross in front of their star as viewed from the Earth's perspective. Their inclination
s relative to Earth's line of sight, or how far above or below the plane of sight they are, vary by a little more than a degree. This allows direct measurements of the planets' periods and relative diameters (compared to the host star) by monitoring each planet's transit of the star. Simulations suggest that the mean mutual inclinations of the planetary orbits are about 1°, meaning the system is probably more coplanar
(flatter) than the Solar System
, where the corresponding figure is 2.3°.
The estimated masses of planets b - f fall in the range between those of Earth
and Neptune
. Their estimated densities, all lower than that of Earth, imply that none of them have an Earth-like composition; a significant hydrogen
atmosphere is indicated for planets d, e and perhaps f, while b and c probably contain substantial amounts of ices
and either hydrogen
and helium
or both. The low densities likely result from high-volume extended atmospheres that surround cores of iron, rock, or both. The inner constituents of the Kepler-11 system were, at the time of their discoveries, the most comprehensively understood extrasolar planets smaller than Neptune.
The system is the most compact known; the orbits of planets b - f would easily fit inside the orbit of Mercury
, with g only slightly outside it. Despite this close packing of the orbits, dynamical integrations indicate the system has the potential to be stable on a time scale of billions of years.
None of the planets are in low-ratio orbital resonance
s, in which multiple planets gravitationally tug on and stabilize each other's orbits, resulting in simple ratios of their orbital periods. However, b and c are close to a 5:4 ratio.
There could conceivably be other planets in the system that do not transit the star, but they would only be detectable by the effects of their gravity on the motion of the visible planets (much as how Neptune was discovered).
Cygnus (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...
, located some 2,000 light years from 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...
. It is located within the field of vision of the Kepler spacecraft, the satellite that 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 Mission
Kepler Mission
The Kepler spacecraft is an American space observatory, the space-based portion of NASA's Kepler Mission to discover Earth-like planets orbiting other stars. The spacecraft is named in honor of the 17th-century German astronomer Johannes Kepler...
uses to detect planets that may be transiting their stars. Announced on February 2, 2011, the star system is the most compact yet discovered and is the flattest known. It is the first discovered case of a star system with six transiting planets. All discovered planets are larger than Earth, with the larger ones being about Neptune's size.
Nomenclature and history
Kepler-11 and its planets were discovered by NASANASA
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 Mission
Kepler Mission
The Kepler spacecraft is an American space observatory, the space-based portion of NASA's Kepler Mission to discover Earth-like planets orbiting other stars. The spacecraft is named in honor of the 17th-century German astronomer Johannes Kepler...
, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits move in front of their stars from the perspective of 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...
. Kepler-11 is the first discovered exoplanetary system with more than three transiting planets.
Kepler-11 is named for the Kepler Mission: it is the 11th star with confirmed planets discovered by Kepler.
The planets are named alphabetically, starting with the innermost: b, c, d, e, f, and g, distinguishers that are tagged onto the name of their home star.
Characteristics
Kepler-11 is a G-type star that is approximately 95% the mass of and 110% the radius of the SunSun
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 has a surface temperature of 5680 (± 100) K and is 8 (± 2) billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K.
The star's 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...
, or how bright it appears from Earth's perspective, is 13.7. Therefore, it cannot be seen with the naked eye.
Planetary system
All known planets transitAstronomical transit
The term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, hiding a small part of it, as seen by an observer at some particular vantage point...
the star; this means that all six planets' orbits appear to cross in front of their star as viewed from the Earth's perspective. Their 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...
s relative to Earth's line of sight, or how far above or below the plane of sight they are, vary by a little more than a degree. This allows direct measurements of the planets' periods and relative diameters (compared to the host star) by monitoring each planet's transit of the star. Simulations suggest that the mean mutual inclinations of the planetary orbits are about 1°, meaning the system is probably more coplanar
Coplanarity
In geometry, a set of points in space is coplanar if all the points lie in the same geometric plane. For example, three distinct points are always coplanar; but a fourth point or more added in space can exist in another plane, incoplanarly....
(flatter) than the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, where the corresponding figure is 2.3°.
The estimated masses of planets b - f fall in the range between those of 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...
and Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
. Their estimated densities, all lower than that of Earth, imply that none of them have an Earth-like composition; a significant hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
atmosphere is indicated for planets d, e and perhaps f, while b and c probably contain substantial amounts of ices
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
and either hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
or both. The low densities likely result from high-volume extended atmospheres that surround cores of iron, rock, or both. The inner constituents of the Kepler-11 system were, at the time of their discoveries, the most comprehensively understood extrasolar planets smaller than Neptune.
The system is the most compact known; the orbits of planets b - f would easily fit inside 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...
, with g only slightly outside it. Despite this close packing of the orbits, dynamical integrations indicate the system has the potential to be stable on a time scale of billions of years.
None of the planets are in low-ratio orbital resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
s, in which multiple planets gravitationally tug on and stabilize each other's orbits, resulting in simple ratios of their orbital periods. However, b and c are close to a 5:4 ratio.
There could conceivably be other planets in the system that do not transit the star, but they would only be detectable by the effects of their gravity on the motion of the visible planets (much as how Neptune was discovered).
| Planet Planet A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,... |
Mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:... (ME 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.... ) |
Radius Radius In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its... (RE 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... ) |
Density Density The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight... (g/cm3) |
Orbital period Orbital period The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of... (d Day A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun... ) |
Semimajor axis (AU Astronomical unit An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance.... ) |
Orbital ecc. |
Inc. 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... (° Degree (angle) A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians... ) |
Discovery year |
|---|---|---|---|---|---|---|---|---|
| b 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... |
4.3 (2.3 - 6.5) | 1.97 ± 0.19 | 3.1 (1.6 - 5.2) | 10.30375 | 0.091 | 0 | 88.5 | 2011 |
| c 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... |
13.5 (7.4 - 18.3) | 3.15 ± 0.30 | 2.3 (1.2 - 3.6) | 13.02502 | 0.106 | 0 | 89 | 2011 |
| d 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... |
6.1 (4.4 - 9.2) | 3.43 ± 0.32 | 0.9 (0.6 - 1.4) | 22.68719 | 0.159 | 0 | 89.3 | 2011 |
| e 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... |
8.4 (6.5 - 10.9) | 4.52 ± 0.43 | 0.5 (0.3 - 0.7) | 31.9959 | 0.194 | 0 | 88.8 | 2011 |
| f 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... |
2.3 (1.1 - 4.5) | 2.61 ± 0.25 | 0.7 (0.3 - 1.4) | 46.68876 | 0.25 | 0 | 89.4 | 2011 |
| g | Unknown | 3.66 ± 0.35 | Unknown | 118.37774 | 0.462 | 0 | 89.8 | 2011 |
Relative size and positions of the 6 planets of Kepler-11, and of the innermost Solar system Solar System The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun... for comparison. The diameters of the planets (but not of the stars!) are scaled up by a factor of 50 times larger than actual scale. |
See also
- List of planetary systems
- Kepler MissionKepler MissionThe Kepler spacecraft is an American space observatory, the space-based portion of NASA's Kepler Mission to discover Earth-like planets orbiting other stars. The spacecraft is named in honor of the 17th-century German astronomer Johannes Kepler...
- Gliese 581Gliese 581Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...
- 55 Cancri55 Cancri55 Cancri , also cataloged Rho1 Cancri or abbreviated 55 Cnc, is a binary star approximately 41 light-years away from Earth in the constellation of Cancer...
- HD 10180HD 10180HD 10180 is a solar-type star. A research team led by Christophe Lovis of the University of Geneva discovered that the star has at least five planets, and possibly as many as seven. It is 127 light-years away, in the southern constellation of Hydrus...