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

In this letter we present the discovery of a very light planetary companion to the star mu Ara (HD160691). 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 m(2) sin i = 14 M-circle times (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.