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⊕ 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⊕ mass and orbits at 0.25 AU 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. Based on observations made with the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory under the GTO programme ID 072.C-0488. Table of radial velocities is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/469/L43