Gliese 1214 b
(often shortened to GJ 1214 b) is an
exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
that orbits the star
Gliese 1214
Extrasolar PlanetsEncyclopaedia
Gliese 1214 is a dim M4.5 red dwarf in the constellation Ophiuchus with an apparent magnitude of 14.7. It is located at a distance of approximately 47 light years from Earth. The star is about one-fifth t ...
, and was discovered in December 2009. Its parent star is 48
light-years from the
Sun, in the constellation
Ophiuchus. As of 2017, GJ 1214 b is the most likely known candidate for being an
ocean planet.
For that reason, scientists have nicknamed the planet "the waterworld".
It is a
super-Earth, meaning it is larger than
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
but is significantly smaller (in mass and radius) than the
gas giants of the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. After
CoRoT-7b
CoRoT-7b (previously named CoRoT-Exo-7b) is an exoplanet orbiting the star CoRoT-7 in the constellation of Monoceros (constellation), Monoceros, from Earth. It was first detected Methods of detecting extrasolar planets#Transit photometry, photome ...
, it was the second super-Earth to have both its mass and radius measured
and is the first of a new class of planets with small size and relatively low density.
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
spectroscopic methods
Applied spectroscopy is the application of various spectroscopic methods for the detection and identification of different elements or compounds to solve problems in fields like forensics, medicine, the oil industry, atmospheric chemistry, and ...
.
In December 2013, NASA reported that
clouds
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may com ...
may have been detected in the
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
of GJ 1214 b.
In August 2022, this planet and its host star were included among 20 systems to be named by the third
NameExoWorlds project.
Detection
GJ 1214 b was first detected by the
MEarth Project
The MEarth Project is a United States NSF-funded, robotic observatory that is part of Fred Lawrence Whipple Observatory on Mt. Hopkins, Arizona, US. The project monitors the brightness of thousands of red dwarf stars with the goal of finding tra ...
, 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
The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...
'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
Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
'' announcing the planet and giving estimates of its mass, radius, and orbital parameters.
Features

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
The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...
.
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.
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 the spectrum to be largely featureless over the wavelength range of 750–1000 nm. Because 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.
Because of the estimated old age of the planetary system and the calculated
hydrodynamic escape (loss of gasses that tends to deplete an atmosphere of higher molecular-weight constituents) rate of 900
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s per second, scientists conclude that there has been a significant atmospheric loss during the lifetime of the planet and any current atmosphere cannot be primordial.
The loss of primordial atmosphere was indirectly confirmed in 2020 as no helium was detected at Gliese 1214 b. Helium was detected in the atmosphere of Gliese 1214 b by 2022 though.
GJ 1214 b may be cooler than any other known
transiting planet
In astronomy, a transit (or astronomical transit) is a phenomenon when a celestial body passes directly between a larger body and the observer. As viewed from a particular vantage point, the transiting body appears to move across the face of th ...
prior to the discovery of
Kepler-16b
Kepler-16b (formally Kepler-16 (AB)-b) is an extrasolar planet. It is a Saturn-mass planet consisting of half gas and half rock and ice, and it orbits a binary star, Kepler-16, with a period of 229 days. " tis the first confirmed, unambiguous e ...
in 2011 by the
Kepler mission. Its
equilibrium temperature is believed to be in the range of , depending on how much of the star's radiation is
reflected into space.
Speculation based on planetary models
While very little is known about GJ 1214 b, there has been speculation as to its specific nature and composition. On the basis of planetary models
it has been suggested that GJ 1214 b has a relatively thick gaseous envelope,
totaling about 5% of planetary mass.
[ It is possible to propose structures by assuming different compositions, guided by scenarios for the formation and evolution of the planet.] GJ 1214 b could be a rocky planet with an outgassed hydrogen-rich atmosphere, a mini-Neptune
A Mini-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet less massive than Neptune but resembling Neptune in that it has a thick hydrogen–helium atmosphere, probably with deep layers of ice, rock or liquid oceans (made ...
, or an ocean planet. If it is a waterworld, it could possibly be thought of as a bigger and hotter version of Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
's Galilean moon
The Galilean moons (), or Galilean satellites, 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 ...
Europa
Europa may refer to:
Places
* Europe
* Europa (Roman province), a province within the Diocese of Thrace
* Europa (Seville Metro), Seville, Spain; a station on the Seville Metro
* Europa City, Paris, France; a planned development
* Europa Cliff ...
. While no scientist has stated to believe GJ 1214 b is an ocean planet, if GJ 1214 b is assumed to be an ocean planet, i.e. the interior is assumed to be composed primarily of a water core surrounded by more water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
, proportions of the total mass consistent with the mass and radius are about 25% rock and 75% water, covered by a thick envelope of gases such as hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
and helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
(c. 0.05%). Water planets could result from inward planetary migration and originate as protoplanets that formed from volatile ice-rich material beyond the snow-line
The climatic snow line is the boundary between a snow-covered and snow-free surface. The actual snow line may adjust seasonally, and be either significantly higher in elevation, or lower. The permanent snow line is the level above which snow wil ...
but that never attained masses sufficient to accrete large amounts of H/He nebular gas. Because of the varying pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
at depth, models of a water world include "steam, liquid, superfluid, high-pressure ices, and plasma phases" of water. Some of the solid-phase water could be in the form of ice VII
Ice VII is a cubic crystalline form of ice. It can be formed from liquid water above 3 GPa (30,000 atmospheres) by lowering its temperature to room temperature, or by decompressing heavy water (D2O) ice VI below 95 K. (Different types of ice, fr ...
.
See also
*COROT-7b
CoRoT-7b (previously named CoRoT-Exo-7b) is an exoplanet orbiting the star CoRoT-7 in the constellation of Monoceros (constellation), Monoceros, from Earth. It was first detected Methods of detecting extrasolar planets#Transit photometry, photome ...
*Gliese 581 c
Gliese 581c (Gl 581c or GJ 581c) is a planet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a s ...
* Gliese 581 d
*Gliese 876 d
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. It was the lowest-mass extrasolar planet apart from the pulsar planets o ...
*HD 149026 b
HD 149026 b, formally named Smertrios , is an extrasolar planet approximately 250 light-years from the Sun in the constellation of Hercules.
The 2.8766-day period planet orbits the yellow subgiant star HD 149026 at a distance of and is notable ...
*Lists of astronomical objects
This is a list of lists, grouped by type of astronomical object.
Solar System
* List of Solar System objects
* List of gravitationally rounded objects of the Solar System
* List of Solar System objects most distant from the Sun
* List of So ...
*
References
External links
Astronomers Find World with Thick, Inhospitable Atmosphere and an Icy Heart
MEarth Project
Hubble reveals a new class of planet
Astronomers have claimed the existence of a new class of planet: a "water-world" with a thick, steamy atmosphere.
An update on the atmosphere of super-Earth GJ1214b
{{Sky, 17, 15, 18.94, +, 4, 57, 49.7, 42
Transiting exoplanets
Exoplanets discovered in 2009
Super-Earths
Ophiuchus (constellation)
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