Letter to the Editor

The HARPS search for southern extra-solar planets ^*,**

XI. Super-Earths (5 and 8 M) in a 3-planet system

¹ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland e-mail: stephane.udry@obs.unige.ch
² Centro de Astronomia e Astrofísica da Universidade de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
³ Laboratoire d'Astrophysique, Observatoire de Grenoble, Université J. Fourier, BP 53, 38041 Grenoble, Cedex 9, France
⁴ Institut d'Astrophysique de Paris, CNRS, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁵ Service d'Aéronomie du CNRS/IPSL, Université de Versailles Saint-Quentin, BP 3, 91371 Verrières-le-Buisson, France

Received: 4 April 2007
Accepted: 9 May 2007

Abstract

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 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 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.