An extrasolar planetary system with three Neptune-mass planets


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.

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Figure 1: Phase-folded radial velocity curves for the three planets.
Figure 2: Radial velocity curve as a function of time.
Figure 3: Dynamical study of the HD 69830 system.


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The data presented here were obtained with the ESO 3.6-m telescope at La Silla Paranal Observatory, Chile. We thank O. Tamuz for the development of the genetic algorithm code, and J. Couetdic for his help in studying the stability of the asteroid belt. We thank the Swiss National Science Foundation (FNRS), the Centre National de la Recherche Scientifique (France) and the Fundação para Ciência e a Tecnologia (Portugal) for their continuous support.

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Correspondence to Christophe Lovis or Michel Mayor.

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Supplementary information

Supplementary Table 1

This table contains the 74 radial velocity measurements of the star HD 69830 that we have obtained with the HARPS instrument. The format is ASCII text with a tabulation as separation character. The first column contains the epoch of the measurements as Barycentric Julian Date (BJD) minus 2,400,000 (for clarity). The second column gives the radial velocity of the star in km s-1 relative to the Solar System barycenter. Finally, the third column gives the uncertainties on the measurements in km s-1. (TXT 2 kb)

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Lovis, C., Mayor, M., Pepe, F. et al. An extrasolar planetary system with three Neptune-mass planets. Nature 441, 305–309 (2006).

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