Last updated August 2, 2025

Gliese 581 g: A Serious Candidate for Habitability

A world on the edge of the habitable zone

Gliese 581 g is an exoplanet presumed to orbit the star Gliese 581, an M3 spectral type red dwarf located about 20.4 light-years from Earth, in the constellation Libra. It was announced in 2010 as a rocky planet located in the habitable zone, meaning at a distance from its star that would allow the presence of liquid water on its surface.

Physical conditions favorable to life?

With a minimum mass estimated at about 3.1 times that of Earth, Gliese 581 g is likely a super-Earth. It completes a full revolution in just 36.6 days, implying that it is probably in synchronous rotation, always showing the same face to its star. This could generate extreme thermal gradients, but also stable temperate zones in the twilight area, conducive to the emergence of life.

A controversial detection

The very existence of Gliese 581 g has been the subject of debate in the scientific community. The radial velocity method, used to detect it, is sensitive to disturbances. Reanalyses of the data have sometimes attributed the signals to artifacts of stellar activity. Nevertheless, its study remains a textbook case for refining detection methods and exploring habitability criteria.

Characteristics of Gliese 581 g
Parameter	Estimated Value	Reference
Planet Type	Rocky Super-Earth	Vogt et al. (2010)
Minimum Mass	3.1 M_⊕	Vogt et al. (2010)
Estimated Radius	1.5 R_⊕ (assumed)	Estimation based on Earth's density
Distance to Star	0.146 AU	Vogt et al. (2010)
Orbital Period	36.6 days	Vogt et al. (2010)
Equilibrium Temperature	223 K (−50 °C)	Selsis et al. (2007)
Host Star	Gliese 581 (Red Dwarf M3V)	SIMBAD Database

Sources: Vogt et al. 2010 (arXiv), NASA ADS, SIMBAD.

Candidates for habitability in our galactic neighborhood

Since the discovery of the first exoplanets, one of the major goals of contemporary astronomy has been to identify worlds located in the habitable zone of their star — that orbital region where the temperature allows the existence of liquid water on the surface. While water is not proof of life, it remains an essential ingredient to its chemistry as we know it. The simultaneous presence of a rocky surface, a stable atmosphere, and moderate irradiation is considered a favorable configuration for the development of life. Below, a summary table lists some of the most promising exoplanets, selected according to rigorous astrophysical criteria.

Exoplanets located in the habitable zone
Name	Mass (M_⊕)	Radius (R_⊕)	Equilibrium Temp. (K)	Distance (ly)	Star	Star Type	Reference
TRAPPIST-1 e	0.692	0.92	251	39	TRAPPIST-1	M8V	Gillon et al. (2017)
Kepler-442 b	2.34	1.34	233	1,206	Kepler-442	K5V	Torres et al. (2015)
Proxima Centauri b	1.27	—	234	4.24	Proxima Centauri	M5.5V	Anglada-Escudé et al. (2016)
Gliese 667 Cc	3.8	—	276	23.6	Gliese 667 C	M1.5V	Anglada-Escudé et al. (2012)
Kepler-186 f	1.4	1.11	188	582	Kepler-186	M1V	Quintana et al. (2014)
Gliese 581 d	6.98	2.2	222	20.4	Gliese 581	M3V	Udry et al. (2007)
Teegarden's Star c	1.05	—	276	12.5	Teegarden's Star	M7V	Zechmeister et al. (2019)
Kepler-62 f	2.8	1.41	208	1,200	Kepler-62	K2V	Borucki et al. (2013)

Data from the NASA Exoplanet Archive, exoplanetarchive.ipac.caltech.edu