Researchers on 21.4.09 confirmed the existence of a rocky Earthlike planet with a mass of 1.9 Earth masses, orbiting in the Gliese 581 system.
Another planet in the four planet system was also found to be lying in the star's habitable zone, the region where liquid water oceans could exist. The findings are the result of over four years of observations using the world's leading low-mass exoplanet hunter, the HARPS spectrograph attached to the 3.6 metre telescope at La Silla in Chile.
The new planet is orbiting far too close to its host star for it to be habitable, however, the seven Earth mass planet lies towards the far edge of the star's habitable zone, orbiting with a period of nearly 67 days. Gliese 581 d is probably too massive to be a rocky planet, it's probably an icy planet that has migrated closer to the star.
Gliese 581 is roughly one-third the mass of the Sun, and with a much lower luminosity. Therefore a planet would need to be situated much closer to this star than our own Sun in order to receive a comparable amount of energy as the Earth. The holy grail of planet hunting will be to find a true Earth twin.