The HARPS search for southern extra-solar planets


We present here the discovery and characterisation of a very light planet around HD 4308. The planet orbits its star in 15.56 days. The circular radial-velocity variation presents a tiny semi-amplitude of 4.1 ms−1 that corresponds to a planetary minimum mass m2 sin i= 14.1 M⊕ (Earth masses). The planet was unveiled by high-precision radial-velocity measurements obtained with the HARPS spectrograph on the ESO 3.6-m telescope. The radial-velocity residuals around the Keplerian solution are 1.3 ms−1, demonstrating the very high quality of the HARPS measurements. Activity and bisector indicators exclude any significant perturbations of stellar intrinsic origin, which supports the planetary interpretation. Contrary to most planet-host stars, HD 4308 has a marked sub-solar metallicity ([Fe/H]=−0.31), raising the possibility that very light planet occurrence might show a different coupling with the parent star’s metallicity than do giant gaseous extra-solar planets. Together with Neptune-mass planets close to their parent stars, the new planet occupies a position in the mass-separation parameter space that is constraining for planet-formation and evolution theories. The question of whether they can be considered as residuals of evaporated gaseous giant planets, ice giants, or super-earth planets is discussed in the context of the latest core-accretion

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@inproceedings{Mayor2005TheHS, title={The HARPS search for southern extra-solar planets}, author={M. Mayor and X. Bonfils and T. Forveille and X. Delfosse and S. Udry and J.-L. Bertaux and H. Beust and F. Bouchy and C. Lovis and F. Pepe and N. C. Santos}, year={2005} }