The following is the Editor's summary of an article published in Nature today:
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.
This is the summary of the article:
Extrasolar 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
And heres the abstract from the article:
An extrasolar planetary system with three Neptune-mass planets
Christophe Lovis
1, Michel Mayor
1, Francesco Pepe
1, Yann Alibert
2, Willy Benz
2, François Bouchy
3,
4, Alexandre C. M. Correia
5, Jacques Laskar
6, Christoph Mordasini
2, Didier Queloz
1, Nuno C. Santos
1,
7,
8, Stéphane Udry
1, Jean-Loup Bertaux
9 and Jean-Pierre Sivan
10
Top of page 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.
Enjoy,
Al.
