Gliese 581 f or Gl 581 f is an unconfirmed planet in the Gliese 581

Gliese 581

Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...

 system, located 20 light years (about 120 trillion miles) 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...

. 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. The planet was detected using radial velocity measurements

Doppler spectroscopy

Doppler spectroscopy, also known as radial velocity measurement, is a spectroscopic method for finding extrasolar planets. It involves the observation of Doppler shifts in the spectrum of the star around which the planet orbits....

 combining the data from the HIRES instrument of the Keck 1 telescope and the HARPS

High Accuracy Radial Velocity Planet Searcher

The High Accuracy Radial velocity Planet Searcher is a high-precision echelle spectrograph installed in 2002 on ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003...

 instrument of ESO's 3.6m telescope at La Silla Observatory

La Silla Observatory

La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory organisation, and several others are partly maintained by ESO...

.

The planet has a minimum mass of 7.0 Earth masses, suggesting that it may be either a large terrestrial planet (super earth) or a gas giant

Gas giant

A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

 similar to Neptune

Neptune

Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

. It orbits at a distance from its star of 0.758 AU, slightly more than Venus

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

's distance from our 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...

, but it is likely to be far too cold at its surface for liquid water.