Editor's Summary

18 May 2006

It's another world


As the techniques used to search for extrasolar planets have been refined, more and more have been discovered (over 170), and they get smaller. In recent years seven 'hot Neptunes' or 'super-Earths' have been detected. These have masses 5–20 times larger than the Earth and are in close-in orbits (periods of 2–15 days) around Sun-like stars. Now the first multiple system of three Neptune-mass planets has been found, with periods of 8.67, 31.6 and (in the 'habitable' zone) 197 days. They are orbiting the nearby star HD 69830. Theoretical calculations favour a mainly rocky composition for both inner planets. The outer planet probably has a significant gaseous envelope surrounding a rocky/icy core: it is the first Neptune-mass object detected inside the habitable zone of a Sun-like star.

News and ViewsExtrasolar planets: A neptunian triplet

Three planets of Neptune mass have been discovered orbiting a Sun-like star known to have an asteroid belt. Exquisite measurements suggest that the search for habitable planets might be easier than assumed.

David Charbonneau

doi:10.1038/441292a

ArticleAn extrasolar planetary system with three Neptune-mass planets

Christophe Lovis, Michel Mayor, Francesco Pepe, Yann Alibert, Willy Benz, François Bouchy, Alexandre C. M. Correia, Jacques Laskar, Christoph Mordasini, Didier Queloz, Nuno C. Santos, Stéphane Udry, Jean-Loup Bertaux & Jean-Pierre Sivan

doi:10.1038/nature04828