GJ 806 b
GJ 806 b is a super-Earth orbiting the M1.5 V star GJ 806 in the constellation Cygnus. It lies about 39 light-years from Earth and was discovered in 2023 using the transit method.
How Big Is GJ 806 b?
GJ 806 b has a radius of 1.33 times that of Earth. Its mass is 1.9 times that of Earth, giving it a density of 4.40 g/cm³ — between that of rocky and gaseous planets.
Is GJ 806 b in the Habitable Zone?
GJ 806 b orbits inside the inner edge of the habitable zone of GJ 806. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 806: 0.132–0.340 AU (conservative: 0.167–0.322 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 806 b
The equilibrium temperature of GJ 806 b is about 940 K (667 °C) — hot enough to melt many metals. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 130 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on GJ 806 b — one full orbit around GJ 806 — lasts just 22.2 hours, shorter than Mercury's 88-day year. It orbits at an average distance of 0.014 AU — closer to its star than Mercury is to the Sun.
How Was GJ 806 b Discovered?
GJ 806 b was discovered in 2023 using the transit method, with observations from Transiting Exoplanet Survey Satellite (TESS).
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is GJ 806 b?
GJ 806 b is 39.3 light-years (12.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 1987. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 691,680 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. GJ 806 b scores 0.30, ranking #1,494 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 806
GJ 806
- Spectral type
- M1.5 V
- Surface temperature
- 3,600 K (Sun: 5,772 K)
- Mass
- 0.41 M☉
- Radius
- 0.41 R☉
- Luminosity
- 0.0260 L☉
- Age
- 5.0 billion years (Sun: 4.6)
The GJ 806 Planetary System
GJ 806 b is one of 2 known planets in the GJ 806 system. Its siblings:
- GJ 806 c (Super Earth)
GJ 806 b — Complete Data
| Radius | 1.331 Earth radii (0.119 Jupiter radii) |
|---|---|
| Mass | 1.90 Earth masses (0.006 Jupiter masses) |
| Density | 4.40 g/cm³ (Earth: 5.51) |
| Orbital period | 0.93 days |
| Orbital distance | 0.014 AU |
| Equilibrium temperature | 940 K (667 °C) |
| Stellar irradiation | 130.00× Earth |
| Earth Similarity Index | 0.30 |
| Distance from Earth | 39.3 light-years (12.0 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2023 |
Data: NASA Exoplanet Archive, last updated 2023-11-28. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 806 b
Is GJ 806 b habitable?
No — GJ 806 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 806 b?
GJ 806 b is about 39 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 691,680 years to get there.
How big is GJ 806 b compared to Earth?
GJ 806 b has 1.33 times the radius of Earth and about 1.9 times its mass.
How long is a year on GJ 806 b?
One orbit around GJ 806 takes 0.9 Earth days — short enough that 394 of its years would fit into one Earth year.
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