The HARPS survey for southern extra-solar planets. II. A 14 Earth-masses exoplanet around μ Arae

In this letter we present the discovery of a very light planetary companion to the star μ Ara (HD 160691). The planet orbits its host once every 9.5 days, and induces a sinusoidal radial velocity signal with a semi-amplitude of 4.1 m s^-1, the smallest Doppler amplitude detected so far. These values imply a mass of m₂ sin i= 14 M_⊕ (Earth-masses). This detection represents the discovery of a planet with a mass slightly smaller than that of Uranus, the smallest ``ice giant'' in our Solar System. Whether this planet can be considered an ice giant or a super-earth planet is discussed in the context of the core-accretion and migration models.

Based on observations collected at La Silla Observatory, ESO, Chile, with the HARPS spectrograph, at the 3.6-m ESO telescope (programs 073.D-0578 and 072.C-0488).