Paris, May 18, 2006
Over the last eleven years, 180 planets have been detected orbiting stars similar to our Sun. The smallest of them have masses between 5 and 20 times that of the Earth and are mostly very close to their star, with orbital periods of just a few days.
The finding obtained by the European team of astronomers describes a new planetary system with features similar to that of our solar system. By using the HARPS spectrograph mounted on the focus of the ESO telescope at La Silla, Chile, the researchers discovered that 3 planets with masses 10, 12 and 18 times that of the Earth are orbiting the star HD69830, with a mass only slightly less than that of our own Sun and an age lying somewhere between 4 and 10 billion years. Simulations show that the three planets, located 0.07, 0.18 and 0.63 AU(2) from their star, are in a stable configuration. Other simulations based on models of planetary formation have shown that the innermost planet should be mainly rocky, the next furthest out should be half rocky, half gaseous, and the outermost planet should have a gaseous envelope surrounding a rocky, icy core. This planet turns out to be located in the habitable zone, i.e. at a distance from the star such that liquid water could be present on the surface of a solid planet.
Moreover, this planetary system, also known as “Neptune's Trident”, has a special feature. Nasa's Spitzer satellite has discovered a strong infrared emission, attributed to an asteroid belt located between the second and third exoplanet, where numerous collisions may be taking place and forming small crystalline silicate grains with diameters of around one micrometer. This observation shows that the system is still evolving.
The study of extra-solar planets has become one of the main areas of research in astronomy, both on the ground and in space, with the ultimate aim of understanding the origin of the solar system, and especially of the Earth and, in the longer term, of searching for life elsewhere in the Universe.
© Institut de Physique de Bern A simplified illustration of the position and internal structure of the three planets in “Neptune's trident”.
© Institut de Physique de Bern
A simplified illustration of the position and internal structure of the three planets in “Neptune's trident”.
1) The team is made up of: C. Lovis, M. Mayor, F. Pepe. D. Queloz, S. Udry: Observatoire de Genève ; YGeneva Observatory; Y. Alibert, W. Benz, C. Mordasini: Université de Berne ; J.L. University of Berne; J.L. Bertaux: Service d'Aéronomie (CNRS, Universités de Paris VI et Versailles St-Quentin) ; J.P. Sivan : Laboratoire d'Astrophysique de Marseille (CNRS, Université Aix-Marseille I) ; F. Bouchy : Service d'Aéronomie (CNRS, Universités de Paris VI et Versailles St-Quentin); J.P. Sivan: Laboratoire d'Astrophysique de Marseille (Marseille Astrophysics Laboratory, CNRS, Université Aix-Marseille I); F. Bouchy: Institut d'Astrophysique de Paris (CNRS, Université Parsi VI) / Observatoire de Haute Provence (CNRS) ; A.C.M. Correia :Institut d'Astrophysique de Paris (Paris Astrophysics Institute, CNRS, Université Paris VI) / Observatoire de Haute Provence (CNRS); A.C.M. Correia: Université de Aveiro, Portugal ; J. University of Aveiro, Portugal; J. Laskar : IMCCE (Observatoire de Paris, CNRS, Université de Paris VI) ; NLaskar: IMCCE (Observatoire de Paris, CNRS, Université de Paris VI); N.C. Santos :C. Santos: Université de Lisbonne, Portugal. University of Lisbon, Portugal.
2) 1 astronomical unit = 150 million km, the distance from the Earth to the Sun.
« An extrasolar planetary system with three Neptune-Mass Planets », Lovis, C., Mayor, M., Pepe, F., Alibert, Y., Benz, W. Bouchy, F., Correia, A.C.M., Laskar, J., Mordasini, C., Queloz, D., Santos, N.C., Udry, S., Bertaux, J.-L., Sivan, J.-P. Nature, 18 May 2006.
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