82 Eridani
Encyclopedia
82 G. Eridani is a star
about 20 light years away from Earth. It is in the constellation Eridanus
. It is a main sequence
star of spectral type G5.
, and uses a similar numbering scheme. 82 G. Eridani, like other stars near the Sun, has held on to its Gould designation, even while other more distant stars have not.
or Alpha Centauri
B. The projected equatorial rotation
rate (
) is a leisurely 0.52 km/s, compared to 2 km/s for the Sun.
82 G. Eridani is a high-velocity star—it is moving quickly compared to the average—and hence is probably a member of Population II, generally older stars whose motions take them well outside the plane of the Milky Way
. Like many other Population II stars, 82 G. Eridani is somewhat metal-deficient (though much less deficient than many), and is older than the Sun. It has a relatively high orbital eccentricity of 0.40 about the galaxy, ranging between 4.6 and 10.8 kiloparsecs from the core. The estimated age of this star is close to the age of the universe
, so it was probably formed early in the history of the Milky Way. A more recent age estimate, based on the star's chromospheric activity, places its age closer to 6 billion years.
This star is located in a region of low-density interstellar matter (ISM), so it is believed to have a large astropause
that subtends an angle of 6″ across the sky. Relative to the Sun, this star is moving at a space velocity of 101 km/s, with the bow shock
advancing at more than Mach 3
through the ISM.
A, Eta Cassiopeiae
A, and Delta Pavonis
. 82 G. Eridani (GJ 139) was also picked as a Tier 1 target star for NASA
's proposed Space Interferometry Mission
(SIM) mission to search for terrestrial-sized
or larger planet
s.
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
about 20 light years away from Earth. It is in the constellation Eridanus
Eridanus (constellation)
Eridanus is a constellation. It is represented as a river; its name is the Ancient Greek name for the Po River. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations. It is the sixth largest of the modern...
. It is a main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star of spectral type G5.
Observation
82 G. Eridani (sometimes abbreviated to "82 Eridani") is the 82nd star in Eridanus in the southern-sky catalog Uranometria Argentina. The Argentina catalog, compiled by the 19th-century astronomer Benjamin Gould, is a southern celestial hemisphere analog of the more famous Flamsteed catalogFlamsteed designation
Flamsteed designations for stars are similar to Bayer designations, except that they use numbers instead of Greek letters. Each star is assigned a number and the Latin genitive of the constellation it lies in...
, and uses a similar numbering scheme. 82 G. Eridani, like other stars near the Sun, has held on to its Gould designation, even while other more distant stars have not.
Properties
In terms of luminosity, 82 G. Eridani is marginally dimmer than the Sun; about 20% more luminous than Tau CetiTau Ceti
Tau Ceti is a star in the constellation Cetus that is spectrally similar to the Sun, although it has only about 78% of the Sun's mass. At a distance of just under 12 light-years from the Solar System, it is a relatively close star. Tau Ceti is metal-deficient and so is thought to be less likely to...
or Alpha Centauri
Alpha Centauri
Alpha Centauri is the brightest star in the southern constellation of Centaurus...
B. The projected equatorial rotation
Stellar rotation
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface....
rate (
) is a leisurely 0.52 km/s, compared to 2 km/s for the Sun.82 G. Eridani is a high-velocity star—it is moving quickly compared to the average—and hence is probably a member of Population II, generally older stars whose motions take them well outside the plane of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
. Like many other Population II stars, 82 G. Eridani is somewhat metal-deficient (though much less deficient than many), and is older than the Sun. It has a relatively high orbital eccentricity of 0.40 about the galaxy, ranging between 4.6 and 10.8 kiloparsecs from the core. The estimated age of this star is close to the age of the universe
Age of the universe
The age of the universe is the time elapsed since the Big Bang posited by the most widely accepted scientific model of cosmology. The best current estimate of the age of the universe is 13.75 ± 0.13 billion years within the Lambda-CDM concordance model...
, so it was probably formed early in the history of the Milky Way. A more recent age estimate, based on the star's chromospheric activity, places its age closer to 6 billion years.
This star is located in a region of low-density interstellar matter (ISM), so it is believed to have a large astropause
Heliosphere
The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
that subtends an angle of 6″ across the sky. Relative to the Sun, this star is moving at a space velocity of 101 km/s, with the bow shock
Heliosphere
The heliosphere is a bubble in space "blown" into the interstellar medium by the solar wind. Although electrically neutral atoms from interstellar volume can penetrate this bubble, virtually all of the material in the heliosphere emanates from the Sun itself...
advancing at more than Mach 3
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
through the ISM.
Planetary system
On August 17, 2011 European astronomers found 3 hot super-Earths around 82 G. Eridani (HD 20794).Habitability
In his book Habitable Planets for Man, Stephen Dole gave 82 G. Eridani his highest estimate for habitability: 5.7%. Four other stars had this figure: Alpha Centauri B, 70 Ophiuchi70 Ophiuchi
70 Ophiuchi a binary star system located 16.6 light years away from the Earth. It is in the constellation Ophiuchus. At magnitude 4 it is a typical less bright star usually visible to the unaided eye away from city lights.-Binary star:...
A, Eta Cassiopeiae
Eta Cassiopeiae
Eta Cassiopeiae is a star system 19.4 light years away from Earth, in the constellation Cassiopeia. Sometimes the traditional name Achird is used....
A, and Delta Pavonis
Delta Pavonis
Delta Pavonis is a star about 19.9 light years away from Earth. It is in the constellation Pavo.-Observations:It is a subgiant of spectral type G8 IV, meaning it is about to stop fusing hydrogen in its core and is starting the process of becoming a red giant. Because of that, Delta Pavonis is...
. 82 G. Eridani (GJ 139) was also picked as a Tier 1 target star for 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 proposed Space Interferometry Mission
Space Interferometry Mission
The Space Interferometry Mission, or SIM, also known as SIM Lite , was a planned space telescope developed by the U.S. National Aeronautics and Space Administration , in conjunction with contractor Northrop Grumman...
(SIM) mission to search for terrestrial-sized
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...
or larger 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,...
s.