GJ 251 c
GJ 251 c is a super-Earth orbiting GJ 251 in the constellation Gemini. It lies about 18 light-years from Earth and was discovered in 2025 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 251 c in the Habitable Zone?
GJ 251 c orbits inside the conservative habitable zone of GJ 251 — 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 251: 0.102–0.267 AU (conservative: 0.129–0.253 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
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Temperature on GJ 251 c
The equilibrium temperature of GJ 251 c is about 216 K (-57 °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 0.40 times the stellar energy that Earth gets from the Sun.
Orbit and Year Length
A year on GJ 251 c — one full orbit around GJ 251 — lasts 53.6 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.196 AU — closer to its star than Mercury is to the Sun.
How Was GJ 251 c Discovered?
GJ 251 c was discovered in 2025 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 251 c?
GJ 251 c is 18.2 light-years (5.6 parsecs) from Earth. Light arriving here tonight left the planet around the year 2008. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 320,320 years to make the journey.
The Host Star: GJ 251
GJ 251
- Surface temperature
- 3,342 K (Sun: 5,772 K)
- Mass
- 0.35 M☉
- Radius
- 0.36 R☉
- Luminosity
- 0.0155 L☉
- Age
- 6.8 billion years (Sun: 4.6)
The GJ 251 Planetary System
GJ 251 c is one of 2 known planets in the GJ 251 system. Its siblings:
- GJ 251 b (Super Earth)
GJ 251 c — Complete Data
| Mass (best estimate) | 3.88 Earth masses |
|---|---|
| Orbital period | 53.65 days |
| Orbital distance | 0.196 AU |
| Equilibrium temperature | 216 K (-57 °C) |
| Stellar irradiation | 0.40× Earth |
| Distance from Earth | 18.2 light-years (5.6 parsecs) |
| Constellation | Gemini |
| Discovery method | Radial Velocity |
| Discovery facility | Multiple Observatories |
| Discovery year | 2025 |
Data: NASA Exoplanet Archive, last updated 2025-10-30. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About GJ 251 c
Is GJ 251 c habitable?
GJ 251 c orbits within the habitable zone of GJ 251, 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 251 c?
GJ 251 c is about 18 light-years from Earth in the constellation Gemini. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 320,320 years to get there.
How long is a year on GJ 251 c?
One orbit around GJ 251 takes 53.6 Earth days.
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