Gliese 581 b is an extrasolar planet orbiting the star Gliese 581. It is the first planet of four (or possibly six) discovered in the system so far. The planet was discovered by a team of French and Swiss astronomers, who announced their findings on November 30, 2005.

Orbital period and massEdit

Gliese 581 b appears to be a Hot Neptune, as it has a minimum mass of about 16 times that of Earth's mass, similar to Neptune's mass. It does not transit its star, implying that its inclination is less than 88.1 degrees. The planet is rather close to Gliese 581 and completes a full orbit in only 5.4 earth days, at a mean distance of about 6 million kilometres (0.041 AU). By comparison, Mercury is at a distance of 58 million kilometres (0.387 AU), and completes an orbit in about 88 days.


Gliese 581 b is about 0.04 AU from its host star, Gliese 581. It is likely close to Gliese 436 b in mass, temperature, (and with Gliese 876 d) susceptibility to solar effects such as coronal mass ejection. Though, since Gliese 581 b does not transit, nothing more can be said yet. The formation between Gliese 436 b and Gliese 581 b must have differed, as Gliese 436 b orbits alone, and Gliese 581 b orbits alongside four - six other planets.