Gliese 876 b
| Exoplanet | List of exoplanets | |
|---|---|---|
| Parent star | ||
| Star | Gliese 876 | |
| Constellation | Aquarius | |
| Right ascension | (α) | 22h 53m 16.734s |
| Declination | (δ) | −14° 15′ 49.32″ |
| Apparent magnitude | (mV) | 10.15 |
| Distance | 15.3 ± 0.2 ly (4.69 ± 0.05 pc) |
|
| Spectral type | M4V | |
| Mass | (m) | 0.334 (± 0.030) M☉ |
| Radius | (r) | 0.36 R☉ |
| Temperature | (T) | 3350 (± 300) K |
| Metallicity | [Fe/H] | 0.05 (± 0.20) |
| Age | 2.55 (± 2.45) Gyr | |
| Physical characteristics | ||
| Mass | (m) | 2.2756 (± 0.0045)MJ |
| Radius | (r) | ~1.2 RJ |
| Stellar flux | (F⊙) | 0.33 ⊕ |
| Temperature | (T) | 194 K (−79 °C; −110 °F) |
|
Orbital elements Epoch HJD 2,450,602.093 |
||
| Semi-major axis | (a) | 0.208317 ± 0.000020AU |
| Eccentricity | (e) | 0.0324 ± 0.0013 |
| Orbital period | (P) | 61.1166 ± 0.0086d |
| Inclination | (i) | 59° |
| Argument of periastron |
(ω) | 50.3 ± 3.2° |
| Mean anomaly | (M) | 325.7 ± 3.2° |
| Semi-amplitude | (K) | 214.00 ± 0.42m/s |
| Discovery information | ||
| Discovery date | June 23, 1998 | |
| Discoverer(s) | California and Carnegie Planet Search Team and independently by the Geneva Extrasolar Planet Search Team | |
| Discovery method | Radial velocity | |
| Other detection methods | Astrometry | |
| Discovery site | Lick, Keck, Haute-Provence and La Silla Observatories | |
| Discovery status | Published | |
| Database references | ||
| Extrasolar Planets Encyclopaedia |
data | |
| SIMBAD | data | |
| Exoplanet Archive | data | |
| Open Exoplanet Catalogue | data | |
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.
Gliese 876 b was discovered independently by two different teams, one led by Geoffrey Marcy (with data from Keck Observatory and Lick Observatory) and the other by Xavier Delfosse (at Geneva Observatory). Like the majority of known extrasolar planets, it was discovered by detecting variations in its star's radial velocity as a result of the planet's gravity. This was done by making sensitive measurements of the Doppler shift of the spectral lines of Gliese 876. It was the first discovered of four known planets in the Gliese 876 system.
Given the planet's high mass, it is likely that Gliese 876 b is a gas giant with no solid surface. Since the planet has only been detected indirectly through its gravitational effects on the star, properties such as its radius, composition, and temperature are unknown. Assuming a composition similar to Jupiter and an environment close to chemical equilibrium, it is predicted that the atmosphere of Gliese 876 b is cloudless, though cooler regions of the planet may be able to form water clouds.
A limitation of the radial velocity method used to detect Gliese 876 b is that only a lower limit on the planet's mass can be obtained. This lower limit is around 1.93 times the mass of Jupiter. The true mass depends on the inclination of the orbit, which in general is unknown. However, because Gliese 876 is only 15 light years from Earth Benedict et al. (2002) were able to use one of the Fine Guidance Sensors on the Hubble Space Telescope to detect the astrometric wobble created by Gliese 876 b. This constituted the first unambiguous astrometric detection of an extrasolar planet. Their analysis suggested that the orbital inclination is 84°±6° (close to edge-on). In the case of Gliese 876 b, modelling the planet-planet interactions from the Laplace resonance shows that the actual inclination of the orbit is 59°, resulting in a true mass of 2.2756 times the mass of Jupiter.
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