GJ 1214 b
Planet· orbits the Sun
GJ 1214 b — a famous 'WATER WORLD' / steam planet: a sub-Neptune of 2.7 Earth radii and ~8.4 Earth masses whose low density and thick, hazy atmosphere point to a world rich in water — likely a deep, hot steam envelope over a rocky-icy interior. Long a mystery because its haze hid its air; in 2023 JWST finally sensed a reflective, water-rich, metal-rich atmosphere. Because it transits with a measured mass, its density is real. Never imaged.
Open in 3D viewSee GJ 1214 b in the live, interactive 3D map
Key facts
Mass
5.02 × 10²⁵ kg
8.41 M⊕
Radius
17,412 km
2.73× wider than Earth
Surface gravity
11.1 m/s²
1.13× Earth's
Year
1.58 Earth days
Distance from GJ 1214
2,251,448 km
Science
Physical
- Mass
- 5.02 × 10²⁵ kg · 8.41 M⊕
- Radius
- 17,412 km · 2.73× wider than Earth
- Density
- 2,271 kg/m³ · 2.3× water
- Surface gravity
- 11.1 m/s² · 1.13× Earth's
- Escape velocity
- 19.6 km/s · 1.75× Earth's
Orbital
- Semi-major axis
- 2,251,448 km
- Eccentricity
- 0.0062
- Inclination
- 0.00 °
- Orbital period
- 37.93 hours
- Perihelion
- 2,237,489 km
- Aphelion
- 2,265,407 km
- Mean orbital velocity
- 104 km/s
Atmosphere
- Composition
- Thick and hazy; JWST (2023) inferred a water-rich, metal-rich ('high-metallicity') steam atmosphere — consistent with a water world.
Composition
- Bulk composition
- A sub-Neptune of 2.7 Earth radii and ~8.4 Earth masses whose low density is real (from transit + mass), and its thick, hazy atmosphere points to a WATER-rich world — likely a deep, hot steam envelope over a rocky-icy interior. For years its haze hid its atmosphere, making it a byword for a 'mystery world'; in 2023 JWST finally sensed a reflective, water-rich, metal-rich atmosphere. Never imaged.
- Cloud appearance
- Appearance based on NASA/JPL-Caltech's artist's concept. No spacecraft has imaged this world, so its real appearance is unknown — The banded clouds shown are a representation of its class, shown only in Vision mode; Realism shows a plain spectral colour.
Radiation & temperature
- Insolation
- 17.2 S⊕ · 17.2× the sunlight Earth receives
- Equilibrium temperature
- 567 K (294 °C)
Discovery & history
- Method
- Transit detection
- Name
- Designated 'b' under the IAU convention that letters a star's planets 'b', 'c'… in the order found (the star is the unwritten 'a'); no IAU proper name is assigned.
Discovered transiting in 2009 by the MEarth project; its flat, featureless spectrum made it a byword for a hazy 'mystery' world until JWST probed it in 2023.
Images
Images from open archives · credit shown per image