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Gliese 581

In April 2007 around this red dwarf the first Earth-like exoplanet has been discovered, Gliese 581 c. This has 1.5 times the diameter and 5 times the mass of Earth and orbits its star every 13 days in a distance of 0.07 AU. Probably the planet has a surface temperature which allows liquid water. This discovery is a real sensation and an important step to the finding of alien life.

Another planet d with 8 times Earth's mass, an orbit period of 84 days and a distance of 0.25 AU, probably has life-friendly temperatures as well.

Already longer known is a planet b with 16.6 times the mass of Earth, which orbits the star every 5.4 days.

In April 2009 Gliese 581 e was discovered, the so far lightest exoplanet with only 1.9 times the mass of Earth. With an orbit period of 3.14 days it is too close to its star for life.

In September 2010 planets f and g were discovered, which have 7 and 3-4 times Earth's mass. f needs for an orbit 433 days and is very cold, whereas g orbits its star with a period of 36.6 days in synchronized rotation and lies in the habitable zone.

Constellation: Libra
Age: 4.3 billion years
Distance: 20.4 light-years
Spectral class: M3.5
Visual magnitude: 10.56
Luminosity: 0.002 * Sun
Mass: 0.33 * Sun
Radial velocity: -9.4 km/sec

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Gliese 581 e b c d
Image: ESO, Franck Selsis, Univ. of Bordeaux.
The four planets and the habitable zone, Gliese 581 compared to the Sun.
    Gliese 581
Graphic: ESO

Gliese 581
Photo: ESO Online Digitized Sky Survey

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