GJ 357 d
GJ 357 d is a super-Earth 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 radial velocity method. It orbits within the habitable zone of its star — the region where liquid water could exist on a planet's surface.
Is GJ 357 d in the Habitable Zone?
GJ 357 d orbits inside the conservative habitable zone of GJ 357 — the region where a rocky planet could sustain liquid water on its surface. This makes it one of the most interesting known exoplanets in the search for life.
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 d
The equilibrium temperature of GJ 357 d is about 220 K (-54 °C) — well below freezing. This estimate ignores any atmosphere, which could change surface temperatures dramatically — Earth's greenhouse effect adds about 33 °C. It receives 0.38 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on GJ 357 d — one full orbit around GJ 357 — lasts 55.7 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.204 AU — closer to its star than Mercury is to the Sun.
How Was GJ 357 d Discovered?
GJ 357 d was discovered in 2019 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 357 d?
GJ 357 d 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 d scores 0.58, ranking #161 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 d is one of 3 known planets in the GJ 357 system. Its siblings:
GJ 357 d — Complete Data
| Mass (best estimate) | 6.10 Earth masses |
|---|---|
| Orbital period | 55.66 days |
| Orbital distance | 0.204 AU |
| Equilibrium temperature | 220 K (-54 °C) |
| Stellar irradiation | 0.38× Earth |
| Earth Similarity Index | 0.58 |
| Distance from Earth | 30.8 light-years (9.4 parsecs) |
| Constellation | Hydra |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2019 |
Data: NASA Exoplanet Archive, last updated 2019-07-29. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 357 d
Is GJ 357 d habitable?
GJ 357 d orbits within the habitable zone of GJ 357, the region where liquid water could exist on a planet's surface. It sits in the conservative habitable zone — the most promising region for habitability. Whether it is actually habitable depends on its atmosphere and composition, which remain unknown.
How far away is GJ 357 d?
GJ 357 d 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 long is a year on GJ 357 d?
One orbit around GJ 357 takes 55.7 Earth days.
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