GJ 357 b
GJ 357 b is a terrestrial planet orbiting the M2.5 V star GJ 357 in the constellation Hydra. It lies about 31 light-years from Earth and was discovered in 2019 using the transit method.
How Big Is GJ 357 b?
GJ 357 b has a radius of 1.20 times that of Earth.
Is GJ 357 b in the Habitable Zone?
GJ 357 b orbits inside the inner edge of the habitable zone of GJ 357. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of GJ 357: 0.101–0.263 AU (conservative: 0.128–0.249 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 357 b
The equilibrium temperature of GJ 357 b is about 518 K (245 °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 357 b — one full orbit around GJ 357 — lasts 3.93 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.036 AU — closer to its star than Mercury is to the Sun.
How Was GJ 357 b Discovered?
GJ 357 b was discovered in 2019 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 357 b?
GJ 357 b is 30.8 light-years (9.4 parsecs) from Earth. Light arriving here tonight left the planet around the year 1996. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 542,080 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 357 b scores 0.40, ranking #491 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: GJ 357
GJ 357
- Spectral type
- M2.5 V
- Surface temperature
- 3,505 K (Sun: 5,772 K)
- Mass
- 0.34 M☉
- Radius
- 0.34 R☉
The GJ 357 Planetary System
GJ 357 b is one of 3 known planets in the GJ 357 system. Its siblings:
GJ 357 b — Complete Data
| Radius | 1.200 Earth radii (0.107 Jupiter radii) |
|---|---|
| Orbital period | 3.93 days |
| Orbital distance | 0.036 AU |
| Equilibrium temperature | 518 K (245 °C) |
| Earth Similarity Index | 0.40 |
| Distance from Earth | 30.8 light-years (9.4 parsecs) |
| Constellation | Hydra |
| Discovery method | Transit |
| Discovery facility | Transiting Exoplanet Survey Satellite (TESS) |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2023-08-22. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 357 b
Is GJ 357 b habitable?
No — GJ 357 b orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is GJ 357 b?
GJ 357 b is about 31 light-years from Earth in the constellation Hydra. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 542,080 years to get there.
How big is GJ 357 b compared to Earth?
GJ 357 b has 1.20 times the radius of Earth.
How long is a year on GJ 357 b?
One orbit around GJ 357 takes 3.9 Earth days — short enough that 93 of its years would fit into one Earth year.
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