Gliese 876

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Gliese 876
Aquarius constellation map.svg
Red Circle(small).svg
Location of Gliese 876 in Aquarius (red dot)
Observation data
Epoch J2000.0       Equinox J2000.0
Constellation Aquarius
Pronunciation /ˈɡlzə/
Right ascension 22h 53m 16.7323s [1]
Declination −14° 15 49.3034 [1]
Apparent magnitude  (V)10.15 [2]
Spectral type M4V [3]
U−B color index 1.15[ citation needed ]
B−V color index 1.59[ citation needed ]
V−R color index 0.30[ citation needed ]
R−I color index 1.22[ citation needed ]
Variable type BY Draconis [4]
Radial velocity (Rv)–1.519 ± 0.157 [5]  km/s
Proper motion (μ)RA: 957.961±0.117 [1]   mas/yr
Dec.: −673.638±0.102 [1]   mas/yr
Parallax (π)213.8669 ± 0.0758 [1]   mas
Distance 15.250 ± 0.005  ly
(4.676 ± 0.002  pc)
Absolute magnitude  (MV)11.79[ citation needed ]
Mass 0.37 [6]   M
Radius 0.3761±0.0059 [6]   R
Luminosity 0.0122±0.0002 [6]   L
Surface gravity (log g)4.89 [7]   cgs
Temperature 3129±19 [6]   K
Metallicity [Fe/H]+0.19 ± 0.17 [8]   dex
Rotation 96.9 [9] days
Rotational velocity (v sin i)0.16, [9]  km/s
Age 0.1–9.9 [9] [10]   Gyr
Other designations
BD-15°6290, G  156-057, GCTP  5546.00, HIP  113020, IL Aquarii, LHS  530, Ross 780, Vys  337
Database references
SIMBAD Gliese 876
Exoplanet Archive data
Extrasolar Planets

Gliese 876 is a red dwarf approximately 15 light-years away from Earth in the constellation of Aquarius. It is the one of the closest known stars to the Sun confirmed to possess a planetary system and the fifth closest such system known to consist of multiple planets (after Wolf 1061, Kapteyn's Star, Tau Ceti and Epsilon Eridani). As of 2018, four extrasolar planets have been found to orbit the star. The planetary system is also notable for the orbital properties of its planets. It is the only known system of orbital companions to exhibit a triple conjunction in the rare phenomenon of Laplace resonance (a type of resonance first noted in Jupiter's inner three Galilean moons). It is also the first extrasolar system around a normal star with measured coplanarity. Two of the middle planets are located in the system's habitable zone; however, they are giant planets believed to be analogous to Jupiter.

Red dwarf An informal category of small, cool stars on the main sequence

A red dwarf is a small and cool star on the main sequence, of M spectral type. Red dwarfs range in mass from about 0.075 to about 0.50 solar mass and have a surface temperature of less than 4,000 K. Sometimes K-type main-sequence stars, with masses between 0.50-0.8 solar mass, are also included.

Light-year unit of length that light travels within one Earthyear; equal to just under 10 trillion kilometres (or about 6 trillion miles)

The light-year is a unit of length used to express astronomical distances and measures about 9.46 trillion kilometres (9.46 x 1012 km) or 5.88 trillion miles (5.88 x 1012 mi). As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word "year", the term light-year is sometimes misinterpreted as a unit of time.

Earth Third planet from the Sun in the Solar System

Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.


Distance and visibility

Gliese 876 is located fairly close to the Solar System. According to astrometric measurements made by the Hipparcos satellite, the star shows a parallax of 213.28 milliarcseconds, [2] which corresponds to a distance of 4.69 parsec s (15.3  ly ), currently making it the third-closest known star with orbiting planets, after Epsilon Eridani and Gliese 674. [9] Despite being located so close to Earth, the star is so faint that it is invisible to the naked eye and can only be seen using a telescope.

Solar System planetary system of the Sun

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

Astrometry part of astronomy, covers star positions and their movements

Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of the Solar System and our galaxy, the Milky Way.

<i>Hipparcos</i> scientific satellite of the European Space Agency

Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permitted the accurate determination of proper motions and parallaxes of stars, allowing a determination of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, this pinpointed all six quantities needed to determine the motion of stars. The resulting Hipparcos Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. Hipparcos' follow-up mission, Gaia, was launched in 2013.

Stellar characteristics

As a red dwarf, Gliese 876 is much less massive than the Sun: estimates suggest it has only 32% of the mass of the Sun. [11] The surface temperature of Gliese 876 is cooler than the Sun and the star has a smaller radius. [12] These factors combine to make the star only 1.24% as luminous as the Sun, and most of this is at infrared wavelengths. Estimating the age and metallicity of cool stars is difficult due to the formation of diatomic molecules in their atmospheres, which makes the spectrum extremely complex. By fitting the observed spectrum to model spectra, it is estimated that Gliese 876 has a slightly lower abundance of heavy elements compared to the Sun (around 75% the solar abundance of iron). [7] Based on chromospheric activity the star is likely to be around 6.5 to 9.9 billion years old, depending on the theoretical model used. [10] However, the low rotational period of the star as well as its membership among the young disk population suggest that the star is between 0.1–5 billion years old. [9] Like many low-mass stars, Gliese 876 is a variable star. Its variable star designation is IL Aquarii and it is classified as a BY Draconis variable. Its brightness fluctuates by around 0.04 magnitudes. [4] This type of variability is thought to be caused by large starspots moving in and out of view as the star rotates. [13] Gliese 876 emits X-rays. [14]

Temperature physical property of matter that quantitatively expresses the common notions of hot and cold

Temperature is a physical quantity expressing hot and cold. It is measured with a thermometer calibrated in one or more temperature scales. The most commonly used scales are the Celsius scale, Fahrenheit scale, and Kelvin scale. The kelvin is the unit of temperature in the International System of Units (SI), in which temperature is one of the seven fundamental base quantities. The Kelvin scale is widely used in science and technology.

Luminosity total amount of energy emitted by an object per unit time

In astronomy, luminosity is the total amount of energy emitted per unit of time by a star, galaxy, or other astronomical object. As a term for energy emitted per unit time, luminosity is synonymous with power.

Infrared electromagnetic radiation with longer wavelengths than those of visible light

Infrared radiation (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye, although IR at wavelengths up to 1050 nanometers (nm)s from specially pulsed lasers can be seen by humans under certain conditions. IR wavelengths extend from the nominal red edge of the visible spectrum at 700 nanometers, to 1 millimeter (300 GHz). Most of the thermal radiation emitted by objects near room temperature is infrared. As with all EMR, IR carries radiant energy and behaves both like a wave and like its quantum particle, the photon.

Planetary system

Observation history

The orbits of the planets of Gliese 876. Note that the strong gravitational interactions between the planets causes rapid orbital precession, so this diagram is only valid at the stated epoch. Gliese876Orbits.svg
The orbits of the planets of Gliese 876. Note that the strong gravitational interactions between the planets causes rapid orbital precession, so this diagram is only valid at the stated epoch.

On June 23, 1998, an extrasolar planet was announced in orbit around Gliese 876 by two independent teams led by Geoffrey Marcy [11] and Xavier Delfosse. [15] The planet was designated Gliese 876 b and was detected by Doppler spectroscopy. Based on luminosity measurement, the circumstellar habitable zone (CHZ) is believed to be located between 0.116 and 0.227 AU. [16] On April 4, 2001, a second planet designated Gliese 876 c was detected, inside the orbit of the previously-discovered planet. [17] The relationship between the orbital periods initially disguised the planet's radial velocity signature as an increased orbital eccentricity of the outer planet. Eugenio Rivera and Jack Lissauer found that the two planets undergo strong gravitational interactions as they orbit the star, causing the orbital elements to change rapidly. [18] On June 13, 2005, further observations by a team led by Rivera revealed a third planet, designated Gliese 876 d inside the orbits of the two Jupiter-size planets. [19] In January 2009, the mutual inclination between planets b and c was determined using a combination of radial velocity and astrometric measurements. The planets were found to be almost coplanar, with an angle of only 5.0+3.9
° between their orbital planes. [20]

Orbit gravitationally curved path of an object around a point in outer space; circular or elliptical path of one object around another object

In physics, an orbit is the gravitationally curved trajectory of an object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit refers to a regularly repeating trajectory, although it may also refer to a non-repeating trajectory. To a close approximation, planets and satellites follow elliptic orbits, with the central mass being orbited at a focal point of the ellipse, as described by Kepler's laws of planetary motion.

Geoffrey Marcy American astronomer

Geoffrey William Marcy is an American astronomer. He is one of the pioneers and leaders in the discovery and characterization of exoplanets. Marcy was Professor of Astronomy at the University of California, Berkeley and an Adjunct Professor of Physics and Astronomy at San Francisco State University before stepping down in October 2015. His colleagues in the Berkeley Astronomy Department forced him to resign after allegations of sexual harassment were substantiated by a Berkeley investigation.

Gliese 876 b is an exoplanet orbiting the red dwarf Gliese 876. It completes one orbit in approximately 61 days. Discovered in June 1998, Gliese 876 b was the first planet to be discovered orbiting a red dwarf.

On June 23, 2010, astronomers announced a fourth planet, designated Gliese 876 e. This discovery better constrained the mass and orbital properties of the other three planets, including the high eccentricity of the innermost planet. [21] This also filled out the system inside e's orbit; additional planets there would be unstable at this system's age. [22] In 2014, reanalysis of the existing radial velocities showed the possible presence of two additional planets. These planets would have almost the same mass as Gliese 876d. [23] In 2018 a study using hundreds of new radial velocity measurements found no evidence for these planets. [24] If this system has a comet disc, it is undetectable "brighter than the fractional dust luminosity 10−5" of a recent Herschel study. [25] None of these planets transit the star from the perspective of Earth, making it difficult to study their properties. [26]

Gliese 876 e extrasolar planet

Gliese 876 e is an exoplanet orbiting the star Gliese 876 in the constellation of Aquarius. It is in a 1:2:4 Laplace resonance with the planets Gliese 876 c and Gliese 876 b: for each orbit of planet e, planet b completes two orbits and planet c completes four. This configuration is the second known example of a Laplace resonance after Jupiter's moons Io, Europa and Ganymede.

Orbital arrangement

Gliese 876 has a notable orbital arrangement. It is the first planetary system around a normal star to have mutual inclination between planets measured without transits (previously the mutual inclination of the planets orbiting the pulsar PSR B1257+12 had been determined by measuring their gravitational interactions [27] ). Later measurements reduced the value of the mutual inclination, [9] and in the latest four-planet models the incorporation mutual inclinations does not result in significant improvements relative to coplanar solutions. [21] The system has the second known example of a Laplace resonance with a 1:2:4 resonance of its planets. The first known example was Jupiter's closest Galilean moons - Ganymede, Europa and Io. Numerical integration indicates that the coplanar, four-planet system is stable for at least another billion years. This planetary system comes close to a triple conjunction between the three outer planets once per orbit of the outermost planet. [21]

Pulsar highly magnetized, rapidly rotating neutron star or white dwarf

A pulsar is a highly magnetized rotating neutron star that emits a beam of electromagnetic radiation. This radiation can be observed only when the beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission. Neutron stars are very dense, and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are believed to be one of the candidates for the source of ultra-high-energy cosmic rays.

PSR B1257+12, previously designated PSR 1257+12, alternatively designated PSR J1300+1240, also named Lich, is a pulsar located 2,300 light-years from the Sun in the constellation of Virgo.

Galilean moons four moons of Jupiter

The Galilean moons are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter in March 1610. They were the first objects found to orbit another planet.


The outermost three of the known planets likely formed further away from the star, and migrated inward. [22]

The Gliese 876 planetary system [21] [note 1]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
d 6.83 ± 0.4  M 0.020806651.9377800.207 ± 0.055
c 0.7142 ± 0.004  MJ 0.129590 ± 0.00002430.0081 ± 0.0080.25591 ± 0.0009
b 2.2756 ± 0.0045  MJ 0.208317 ± 0.0000261.1166 ± 0.00860.0324 ± 0.0013
e 14.6 ± 1.7  M 0.3343 ± 0.0013124.26 ± 0.700.055 ± 0.012
Gliese 876 d

Gliese 876d, discovered in 2005, is the innermost known planet. With an estimated minimum mass only 5.88 times that of the Earth, it is possible that it is a dense terrestrial planet.

Gliese 876 c

Gliese 876 c, discovered in 2001, is a giant planet at 0.62 Jupiter-mass planet. It is in a 1:2 orbital resonance with the outermost known planet, taking 30.340 days to orbit the star. The planet orbits within the habitable zone. Its mass makes it more likely to be a Class II planet in the Sudarsky extrasolar planet classification. The presence of surface liquid water is possible on sufficiently massive satellites should they exist.

Gliese 876 b

Gliese 876 b, discovered in 1998 is around twice the mass of Jupiter and revolves around its star in an orbit taking approximately 61  days to complete, at a distance of only 0.208  AU, less than the distance from the Sun to Mercury. [28] Its mass makes it more likely to be a Class II or Class III planet in the Sudarsky model. The presence of surface liquid water is possible on sufficiently massive satellites should they exist.

Gliese 876 e

Gliese 876 e, discovered in 2010, has a mass similar to that of the planet Uranus and its orbit takes 124 days to complete.

See also


  1. Uncertainties in the planetary masses and semimajor axes do not take into account the uncertainty in the mass of the star.

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Coordinates: Celestia.png 22h 53m 16.7s, −14° 15′ 49″