The HARPS search for southern extra-solar planets -: XI.: Super-Earths (5 and 8 M⊕) in a 3-planet system

This Letter reports on the detection of two super-Earth planets in the Gl 581 system, which is already known to harbour a hot Neptune. One of the planets has a mass of 5 M-circle plus and resides at the warm edge of the habitable zone of the star. It is thus the known exoplanet that most resembles our own Earth. The other planet has a 7.7 M-circle plus mass and orbits at 0.25AU from the star, close to the cold edge of the habitable zone. These two new light planets around an M3 dwarf further confirm the formerly tentative statistical trend toward (i) many more very low-mass planets being found around M dwarfs than around solar-type stars and (ii) low-mass planets outnumbering Jovian planets around M dwarfs.