GJ 3942 b
GJ 3942 b is a super-Earth orbiting the M0 star GJ 3942 in the constellation Draco. It lies about 55 light-years from Earth and was discovered in 2017 using the radial velocity method.
Is GJ 3942 b in the Habitable Zone?
GJ 3942 b orbits inside the inner edge of the habitable zone of GJ 3942. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 3942: 0.224–0.571 AU (conservative: 0.284–0.541 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 3942 b
The equilibrium temperature of GJ 3942 b is about 590 K (317 °C) — hotter than anywhere on Earth. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C.
Orbit and Year Length
A year on GJ 3942 b — one full orbit around GJ 3942 — lasts 6.91 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.061 AU — closer to its star than Mercury is to the Sun. Its orbit is mildly elliptical (eccentricity 0.12).
How Was GJ 3942 b Discovered?
GJ 3942 b was discovered in 2017 using the radial velocity method, with observations from Roque de los Muchachos Observatory.
The radial velocity method measures the subtle wobble of a star caused by the gravitational pull of an orbiting planet, visible as periodic shifts in the star's light spectrum. The size of the wobble reveals the planet's minimum mass.
How Far Away Is GJ 3942 b?
GJ 3942 b is 55.2 light-years (16.9 parsecs) from Earth. Light arriving here tonight left the planet around the year 1971. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 971,520 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 3942 b scores 0.29, ranking #2,005 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 3942
GJ 3942
- Spectral type
- M0
- Surface temperature
- 3,867 K (Sun: 5,772 K)
- Mass
- 0.63 M☉
- Radius
- 0.61 R☉
- Luminosity
- 0.0759 L☉
Planetary System
GJ 3942 b is the only planet known to orbit GJ 3942 so far.
GJ 3942 b — Complete Data
| Mass (best estimate) | 7.14 Earth masses |
|---|---|
| Orbital period | 6.91 days |
| Orbital distance | 0.061 AU |
| Eccentricity | 0.121 |
| Equilibrium temperature | 590 K (317 °C) |
| Earth Similarity Index | 0.29 |
| Distance from Earth | 55.2 light-years (16.9 parsecs) |
| Constellation | Draco |
| Discovery method | Radial Velocity |
| Discovery facility | Roque de los Muchachos Observatory |
| Discovery year | 2017 |
Data: NASA Exoplanet Archive, last updated 2017-12-19. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 3942 b
Is GJ 3942 b habitable?
No — GJ 3942 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 3942 b?
GJ 3942 b is about 55 light-years from Earth in the constellation Draco. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 971,520 years to get there.
How long is a year on GJ 3942 b?
One orbit around GJ 3942 takes 6.9 Earth days — short enough that 53 of its years would fit into one Earth year.
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