Gliese 581 D - Orbital Characteristics

Orbital Characteristics

Gliese 581 d orbits Gliese 581 at 0.21847 AU, approximately a fifth of the distance that the Earth orbits the Sun, though its orbital eccentricity has not been confirmed. There are currently two models for its orbit, a circular one like Earth's, and an eccentric one like Mercury's. These are based on the four planet and six planet model for the Gliese 581 system, respectively. Under the four planet model Gliese 581 d would most probably be in a spin-orbit resonance of 2:1, rotating twice for each orbit of its parent star. Therefore the day on Gliese 581 d should approximately be 67 Earth’s days long.

The orbital distance places it at the outer limits of the habitable zone, the distance at which it is believed possible for water to exist on the surface of a planetary body. At the time of its discovery, the planet's orbit was originally believed to be farther out, however in late April of 2009 the original discovery team revised its original estimate of the planet's orbital parameters, finding that it orbits closer to its star than originally believed with an orbital period of 66.87 days. They concluded that the planet is within the habitable zone where liquid water could exist.