Gliese 581 is a red dwarf

Red dwarf

According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....

 star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 with spectral type

Stellar classification

In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...

 M3V, located 20.3 light years away from Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 in the constellation

Constellation

In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Libra

Libra (constellation)

Libra is a constellation of the zodiac. Its name is Latin for weighing scales, and its symbol is . It is fairly faint, with no first magnitude stars, and lies between Virgo to the west and Scorpius to the east.-Notable features:]...

. Its estimated mass is about a third of that of the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, and it is the 89th closest known star system

Star system

A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...

 to the Sun. Observations suggest that the star has at least six planets: Gliese 581 e

Gliese 581 e

Gliese 581 e or Gl 581 e is an extrasolar planet found around Gliese 581, an M3V red dwarf star approximately 20.5 light-years away from Earth in the constellation of Libra...

, b

Gliese 581 b

Gliese 581 b or Gl 581 b is an extrasolar planet orbiting the star Gliese 581. It is the first planet of six discovered in the system so far, and the second in order from the star.- Discovery :...

, c

Gliese 581 c

Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, d

Gliese 581 d

Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra. It is the third planet discovered in the system and the fifth in order from the star....

, f

Gliese 581 f

Gliese 581 f or Gl 581 f is an unconfirmed planet in the Gliese 581 system, located 20 light years from Earth. It is the fifth planet discovered in the system and the sixth known in order from the star. Its discovery was announced September 29, 2010...

 and g

Gliese 581 g

Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

. g

Gliese 581 g

Gliese 581 g , also Gl 581 g or GJ 581 g, is a hypothesized extrasolar planet proven nonexistent by the Geneva Team, orbiting the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth...

 is thought to be a candidate for habitability.

Gliese 581 has been the subject of a "huge amount of attention" in the quest to discover the first habitable planet

Planetary habitability

Planetary habitability is the measure of a planet's or a natural satellite's potential to sustain life. Life may develop directly on a planet or satellite or be transferred to it from another body, a theoretical process known as panspermia...

; in 2010, attention focused on unconfirmed planet g, which would have been close to the middle of the star's habitable zone

Habitable zone

In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, but more recently, in a study published in The Astrophysical Journal Letters, planet d "can be considered the first confirmed exoplanet that could support Earth-like life."

The star system first gained attention after Gliese 581 c

Gliese 581 c

Gliese 581 c or Gl 581 c is a planet orbiting the red dwarf star Gliese 581. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.6 times that of the Earth, it is classified as a super-Earth...

, the first low-mass extrasolar planet

Extrasolar planet

An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...

 found to be near its star's habitable zone

Habitable zone

In astronomy and astrobiology, a habitable zone is an umbrella term for regions that are considered favourable to life. The concept is inferred from the empirical study of conditions favourable for Life on Earth...

, was discovered in April 2007.