Epoch J2000.0 Equinox J2000.0
|Right ascension||22h 53m 16.7323s|
|Declination||−14° 15′ 49.3034″|
|Apparent magnitude (V)||10.15|
|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|
|Radial velocity (Rv)||–1.519 ± 0.157 km/s|
|Proper motion (μ)||RA: ±0.117 957.961 mas/yr |
Dec.: ±0.102 −673.638 mas/yr
|Parallax (π)||213.8669 ± 0.0758 mas|
|Distance||15.250 ± 0.005 ly |
(4.676 ± 0.002 pc)
|Absolute magnitude (MV)||11.79[ citation needed ]|
|Radius||±0.0059 0.3761 R☉|
|Luminosity||±0.0002 0.0122 L☉|
|Surface gravity (log g)||4.89 cgs|
|Temperature||±19 3129 K|
|Metallicity [Fe/H]||+0.19 ± 0.17 dex|
|Rotational velocity (v sin i)||0.16, km/s|
| 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.
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.
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 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.
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, 4.69 parsec s (15.3 ly ), currently making it the third-closest known star with orbiting planets, after Epsilon Eridani and Gliese 674. 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.which corresponds to a distance of
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 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.
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.
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.The surface temperature of Gliese 876 is cooler than the Sun and the star has a smaller radius. 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). 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. 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. 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. This type of variability is thought to be caused by large starspots moving in and out of view as the star rotates. Gliese 876 emits X-rays.
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.
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 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.
On June 23, 1998, an extrasolar planet was announced in orbit around Gliese 876 by two independent teams led by Geoffrey Marcy and Xavier Delfosse. 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. On April 4, 2001, a second planet designated Gliese 876 c was detected, inside the orbit of the previously-discovered planet. 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. 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. 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
−2.3° between their orbital planes.
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 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. This also filled out the system inside e's orbit; additional planets there would be unstable at this system's age. 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. In 2018 a study using hundreds of new radial velocity measurements found no evidence for these planets. If this system has a comet disc, it is undetectable "brighter than the fractional dust luminosity 10−5" of a recent Herschel study. None of these planets transit the star from the perspective of Earth, making it difficult to study their properties.
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.
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). Later measurements reduced the value of the mutual inclination, and in the latest four-planet models the incorporation mutual inclinations does not result in significant improvements relative to coplanar solutions. 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.
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.
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.
(in order from star)
|Mass|| Semimajor axis |
| Orbital period |
|d||6.83 ± 0.4 M⊕||0.02080665||1.937780||0.207 ± 0.055||—||—|
|c||0.7142 ± 0.004 MJ||0.129590 ± 0.000024||30.0081 ± 0.008||0.25591 ± 0.0009||—||—|
|b||2.2756 ± 0.0045 MJ||0.208317 ± 0.00002||61.1166 ± 0.0086||0.0324 ± 0.0013||—||—|
|e||14.6 ± 1.7 M⊕||0.3343 ± 0.0013||124.26 ± 0.70||0.055 ± 0.012||—||—|
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, 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, 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. 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, discovered in 2010, has a mass similar to that of the planet Uranus and its orbit takes 124 days to complete.
HD 37124 is a yellow dwarf star approximately 103 light-years away in the constellation of Taurus. Three extrasolar planets have been found to orbit the star.
HD 74156 is a yellow dwarf star in the constellation of Hydra, 210 light years from the Solar System. It is known to be orbited by two giant planets.
Gliese 436 is a red dwarf approximately 31.8 light-years away in the zodiac constellation of Leo. It has an apparent visual magnitude of 10.67, which is much too faint to be seen with the naked eye. However, it can be viewed with even a modest telescope of 2.4 in (6 cm) aperture. In 2004, the existence of an extrasolar planet, Gliese 436b, was verified as orbiting the star. This planet was later discovered to transit its host star.
54 Piscium is an orange dwarf star approximately 36 light-years away in the constellation of Pisces. In 2002, an extrasolar planet was confirmed to be orbiting the star, and in 2006, a brown dwarf was also discovered orbiting it.
Gliese 777, often abbreviated as Gl 777 or GJ 777, is a yellow subgiant approximately 52 light-years away in the constellation of Cygnus. The system is also a binary star system made up of two stars and possibly a third. As of 2005, two extrasolar planets are known to orbit the primary star.
Gliese 581 is a star of spectral type M3V at the center of the Gliese 581 planetary system, about 20 light years away from Earth in the Libra constellation. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star to the Sun.
HD 1237 is a binary star system approximately 57 light-years away in the constellation of Hydrus.
HD 73526 is a G-type main-sequence star. It is about 310 light-years away in the constellation Vela.
Gliese 876 d is an exoplanet approximately 15 light-years away in the constellation of Aquarius. The planet was the third planet discovered orbiting the red dwarf Gliese 876. At the time of its discovery, the planet had the lowest mass of any known extrasolar planet apart from the pulsar planets orbiting PSR B1257+12. Due to this low mass, it can be categorized as a super-Earth.
Gliese 876 c is an exoplanet orbiting the red dwarf Gliese 876, taking about 30 days to complete an orbit. The planet was discovered in April 2001 and is the third planet in order of increasing distance from its star.
Gliese 436 b is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436. It was the first hot Neptune discovered with certainty and was among the smallest-known transiting planets in mass and radius, until the much smaller Kepler exoplanet discoveries started coming in by 2010.
A super-Earth is an extrasolar planet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 15 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, as suggested by MIT professor Sara Seager, although "mini-Neptunes" is a more common term.
HD 70642 is a yellow dwarf star in the constellation of Puppis located 92 light years away. This star has about the same mass and radius as the Sun, is slightly cooler and less luminous, and is richer in abundance of iron relative to hydrogen.
Pi Mensae, also known as HD 39091, is a yellow dwarf star in the constellation of Mensa. This star has a high proper motion. The apparent magnitude is 5.67, which can be visible to the naked eye in exceptionally dark, clear skies. It is nearly 60 ly away. The star is slightly larger than the Sun in terms of mass, size, luminosity, temperature, and metallicity and is about 730 million years younger. It hosts two planets.
Gliese 849 is a M3.5V red dwarf star approximately 29 light years away in the constellation of Aquarius. It has the first planet discovered orbiting a red dwarf with a semi-major axis greater than 0.21 AU.
Gliese 317 is a red dwarf approximately 50 light-years away in the constellation of Pyxis. As of 2011, two extrasolar planets have been confirmed to be orbiting the star. Photometric calibrations and infrared spectroscopic measurements indicate that the star is enriched in heavy elements compared to the Sun.
Gliese 86 is a K-type main-sequence star approximately 35 light-years away in the constellation of Eridanus. It has been confirmed that a white dwarf orbits the primary star. In 1998 the European Southern Observatory announced that an extrasolar planet was orbiting the star.
Gliese 3021 b, also known as GJ 3021 b or HD 1237 b, is an extrasolar planet approximately 57 light-years away, orbiting its bright G-dwarf parent star in the Southern constellation of Hydrus. It was discovered with the Swiss Euler Telescope at the Chilean La Silla Observatory in 2000.
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