GJ 393 b
GJ 393 b is a terrestrial planet orbiting the M2.0 V star GJ 393 in the constellation Sextans. It lies about 23 light-years from Earth and was discovered in 2021 using the radial velocity method.
Is GJ 393 b in the Habitable Zone?
GJ 393 b orbits inside the inner edge of the habitable zone of GJ 393. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 393: 0.134–0.346 AU (conservative: 0.170–0.328 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 393 b
The equilibrium temperature of GJ 393 b is about 485 K (212 °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. It receives 9.21 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on GJ 393 b — one full orbit around GJ 393 — lasts 7.03 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.054 AU — closer to its star than Mercury is to the Sun.
How Was GJ 393 b Discovered?
GJ 393 b was discovered in 2021 using the radial velocity method, with observations from Multiple Observatories.
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 393 b?
GJ 393 b is 22.9 light-years (7.0 parsecs) from Earth. Light arriving here tonight left the planet around the year 2004. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 403,040 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 393 b scores 0.43, ranking #394 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 393
GJ 393
- Spectral type
- M2.0 V
- Surface temperature
- 3,579 K (Sun: 5,772 K)
- Mass
- 0.43 M☉
- Radius
- 0.43 R☉
- Luminosity
- 0.0269 L☉
Planetary System
GJ 393 b is the only planet known to orbit GJ 393 so far.
GJ 393 b — Complete Data
| Mass (best estimate) | 1.71 Earth masses |
|---|---|
| Orbital period | 7.03 days |
| Orbital distance | 0.054 AU |
| Equilibrium temperature | 485 K (212 °C) |
| Stellar irradiation | 9.21× Earth |
| Earth Similarity Index | 0.43 |
| Distance from Earth | 22.9 light-years (7.0 parsecs) |
| Constellation | Sextans |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2021 |
Data: NASA Exoplanet Archive, last updated 2021-07-12. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 393 b
Is GJ 393 b habitable?
No — GJ 393 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 393 b?
GJ 393 b is about 23 light-years from Earth in the constellation Sextans. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 403,040 years to get there.
How long is a year on GJ 393 b?
One orbit around GJ 393 takes 7.0 Earth days — short enough that 52 of its years would fit into one Earth year.
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