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Gliese 581b is an extrasolar planet orbiting the red dwarf star Gliese 581. It is the second planet in order of the three currently known, and was the first planet in the Gliese 581 system to be discovered. The planet was announced on November 30, 2005 and was discovered by a team of French and Swiss astronomers. It was the fifth planet discovered orbiting a red dwarf star, after Gliese 876's planets and Gliese 436 b. It lies about 20 light years away from Earth in the constellation of Libra.

CharacteristicsEdit

Mass, orbit, and temperatureEdit

Gliese 581b has a minimum mass of about 15.8 times that of Earth's. This is similar to Neptune's mass, which implies that the planet may be a Hot Neptune. It is very close to Gliese 581, and completes an orbit every 5.4 days. It is likely close to Gliese 436 b in mass and temperature. The planet does not transit its star which implies its inclination is less than 88.1 degrees. It has a highly circular orbit. Not much is known about the characteristics of this planet since it does not transit its host star.

The planet has an equilibrium temperature of about 420 K (147 °C; 297 °F).