title: An extrasolar planetary system with three Neptune-mass planets.
abstract: Over the past two years, the search for low-mass extrasolar planets has led to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around Sun-like stars. These planets have masses 5-20 times larger than the Earth and are mainly found on close-in orbits with periods of 2-15 days. Here we report a system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days, orbiting the nearby star HD 69830. This star was already known to show an infrared excess possibly caused by an asteroid belt within 1 au (the Sun-Earth distance). Simulations show that the system is in a dynamically stable configuration. Theoretical calculations favour a mainly rocky composition for both inner planets, while the outer planet probably has a significant gaseous envelope surrounding its rocky/icy core; the outer planet orbits within the habitable zone of this star.
authors.affiliation: Observatoire de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland. christophe.lovis@obs.unige.ch
authors.forename: Christophe
authors.initials: C
authors.lastname: Lovis
authors.forename: Michel
authors.initials: M
authors.lastname: Mayor
authors.forename: Francesco
authors.initials: F
authors.lastname: Pepe
authors.forename: Yann
authors.initials: Y
authors.lastname: Alibert
authors.forename: Willy
authors.initials: W
authors.lastname: Benz
authors.forename: François
authors.initials: F
authors.lastname: Bouchy
authors.forename: Alexandre C M
authors.initials: AC
authors.lastname: Correia
authors.forename: Jacques
authors.initials: J
authors.lastname: Laskar
authors.forename: Christoph
authors.initials: C
authors.lastname: Mordasini
authors.forename: Didier
authors.initials: D
authors.lastname: Queloz
authors.forename: Nuno C
authors.initials: NC
authors.lastname: Santos
authors.forename: Stéphane
authors.initials: S
authors.lastname: Udry
authors.forename: Jean-Loup
authors.initials: JL
authors.lastname: Bertaux
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Sivan