| Extrasolar planet | List of extrasolar planets | |
|---|---|---|
| Parent star | ||
| Star | GJ 1214 | |
| Constellation | Ophiuchus | |
| Right ascension | (α) | 17h 15m 18.94s |
| Declination | (δ) | +04° 57′ 49.7″ |
| Apparent magnitude | (mV) | 14.67 |
| Distance | 40 ly (13 pc) |
|
| Spectral type | M4.5 | |
| Mass | (m) | 0.157 M☉ |
| Radius | (r) | 0.211 R☉ |
| Temperature | (T) | 3026 K |
| Age | 6 Gyr | |
| Orbital elements | ||
| Semimajor axis | (a) | 0.0143 ± 0.0019 AU (2.14 Gm) |
| 1.1 mas | ||
| Eccentricity | (e) | < 0.27 |
| Orbital period | (P) | 1.5803925 ± 0.0000117 d (0.004326803 y) |
| (37.92942 h) | ||
| Orbital speed | (υ) | 99 km/s |
| Inclination | (i) | 88.62+0.36 −0.28° |
| Time of transit | (Tt) | 2,454,999.712703 ± 0.000126 JD |
| Physical characteristics | ||
| Mass | (m) | 6.55 ± 0.98 (HARPS)[1] M⊕ |
| Radius | (r) | 2.678 ± 0.13 R⊕ |
| Density | (ρ) | 1870 ± 400 kg m-3 |
| Surface gravity | (g) | 0.91 g |
| Temperature | (T) | 393–555 (equilibrium)[1] K |
| Discovery information | ||
| Discovery date | December 16, 2009 | |
| Discoverer(s) | David Charbonneau, et.al. | |
| Detection method | Transit (MEarth Project) | |
| Discovery site | Fred Lawrence Whipple Observatory | |
| Discovery status | Published[1] | |
| Database references | ||
| Extrasolar Planets Encyclopaedia |
data | |
| SIMBAD | data | |
GJ 1214 b is an extrasolar planet that orbits the star GJ 1214, in the constellation Ophiuchus at a distance of 13 parsecs (approximately 40 light-years) from the Sun. The planet was discovered in December 2009. It is classified as a super-Earth because it is larger than Earth but has a mass and radius significantly less than those of the gas giants in the Solar System. After COROT-7b, it is the second such planet to be known[1] and is the first of a new class of planets with small size and relatively low density.[2] GJ 1214 b is also significant because its parent star is relatively near the Sun and because it transits (crosses in front of) that parent star, which allows the planet's atmosphere to be studied using current technologies.[1]
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GJ 1214 b was first detected by the MEarth Project, which searches for the small drops in brightness that can occur when an orbiting planet briefly passes in front of its parent star. In early 2009, the astronomers running the project noticed that the star GJ 1214 appeared to show drops in brightness of that sort. They then observed the star more closely and confirmed that it dimmed by roughly 1.5% every 1.58 days. Follow-up radial-velocity measurements were then made with the HARPS spectrograph on the ESO's 3.6-meter telescope at La Silla, Chile; those measurements succeeded in providing independent evidence for the reality of the planet. A paper was then published in Nature announcing the planet and giving estimates of its mass, radius, and orbital parameters.[1]
The radius of GJ 1214 b can be inferred from the amount of dimming seen when the planet crosses in front of its parent star as viewed from Earth. The mass of the planet can be inferred from sensitive observations of the parent star's radial velocity, measured through small shifts in stellar spectral lines due to the Doppler effect.[1] Given the planet's mass and radius, its density can be calculated. Through a comparison with theoretical models, the density in turn provides limited but highly useful information about the composition and structure of the planet.[1]
On that basis,[3] it has been suggested that GJ 1214 b has a relatively thick gaseous envelope.[2] It is possible to propose structures by assuming different compositions, guided by scenarios for the formation and evolution of the planet.[2] GJ 1214 b could be a rocky planet with an outgassed hydrogen-rich atmosphere, a mini-Neptune, or an ocean planet.[2] If it is a water world it could possibly be thought of as a bigger and hotter version of Jupiter's Galilean moons.[2] If GJ 1214 b is assumed to be an ocean planet,[3] i.e. the interior is assumed to be composed primarily of a rocky core surrounded by water, proportions of the total mass consistent with the mass and radius are ~25% rock and ~75% water, covered by a thick envelope of gases such as hydrogen and helium (~0.05%).[1][4] Water planets could result from inward planetary migration and originate as protoplanets that formed from volatile ice-rich material beyond the snow-line but that never attained masses sufficient to accrete large amounts of H/He nebular gas.[2] Because of the varying pressure at depth, models of a water world include "steam, liquid, superfluid, high-pressure ices, and plasma phases" of water.[2] Some of the solid-phase water could be in the form of ice VII.[4]
Due to the relatively small size of GJ 1214 b's parent star, it is feasible to perform spectroscopic observations during planetary transits. By comparing the observed spectrum before and during transits, the spectrum of the planetary atmosphere can be inferred. In December 2010, a study was published showing that spectrum to be largely featureless over the wavelength range of 750–1000 nm. Since a thick and cloud-free hydrogen-rich atmosphere would have produced detectable spectral features, such an atmosphere appears to be ruled out. Although no clear signs were observed of water vapor or any other molecule, the authors of the study believe the planet may have an atmosphere composed mainly of water vapor. Another possibility is that there may be a thick layer of high clouds, which absorbs the starlight.[5] Further observations are necessary to determine the composition of its atmosphere.
Though a planetary atmosphere has not yet been directly confirmed, the relative close proximity of the planet should allow existing space-based telescopes, such as the Hubble Space Telescope, to detect and characterize one if it exists.[4] Because of the estimated old age of the planetary system and the calculated hydrodynamic escape rate of 9×105 kg s−1, scientists conclude that there has been a significant atmospheric loss during the lifetime of the planet and any current atmosphere cannot be primordial.[1]
GJ 1214 b may be cooler than any other known transiting planet prior to the discovery of Kepler-16b in 2011 by the Kepler mission. Its equilibrium temperature could be between approximately 393–555 K (120–282°C or 248–540°F), depending on how much of the star's radiation is reflected back into space.[1][4]
Media related to [//commons.wikimedia.org/wiki/Category:GJ_1214_b GJ 1214 b] at Wikimedia Commons
Coordinates: 17h 15m 18.94s, +4° 57′ 49.7″
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