Gliese 581c

Gliese 581c

Size comparison of Gliese 581c with Earth and Neptune (based on selected hypothetical modeled compositions)
Discovery[1]
Discovered by	Stéphane Udry et al.
Discovery site	La Silla Observatory
Discovery date	4 April 2007 24 April 2007 (announced)
Detection method	Radial velocity
Orbital characteristics[2]
Semi-major axis	0.074±0.001 AU
Eccentricity	0.087+0.150 −0.016
Orbital period (sidereal)	12.919+0.003 −0.002 d
Time of periastron	2454759.2 ± 0.1[3]
Argument of periastron	148.7°+71.5° −33.0°
Semi-amplitude	3.28+0.22 −0.12 m/s
Star	Gliese 581[4]
Physical characteristics[2]
Mass	≥5.652+0.386 −0.239 M🜨

Gliese 581c /ˈɡliːzə/ (Gl 581c or GJ 581c) is an exoplanet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a super-Earth (a category of planets with masses greater than Earth's up to ten Earth masses).

Gliese 581c gained interest from astronomers because it was reported to be the first potentially Earth-like planet in the habitable zone of its star, with a temperature right for liquid water on its surface, and, by extension, potentially capable of supporting extremophile forms of Earth-like life. However, further research casts doubt upon the planet's habitability. It is tidally locked (always presents the same face to the object it is orbiting) so if life had a chance to emerge, the best hope of survival would be in the "terminator zone".

In astronomical terms, the Gliese 581 system is relatively close to Earth, at 20.55 light-years (194 trillion kilometres; 121 trillion miles) in the direction of the constellation of Libra. This distance, along with the declination and right ascension coordinates, give its exact location in the Milky Way.