Letter to the Editor

The HARPS survey for southern extra-solar planets^*

II. A 14 Earth-masses exoplanet around μ Arae

¹ Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal e-mail: nuno.santos@oal.ul.pt
² Observatoire de Genève, 51 ch. des Maillettes, 1290 Sauverny, Switzerland
³ Laboratoire d'Astrophysique de Marseille, Traverse du Siphon, 13013 Marseille, France
⁴ Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France
⁵ Physikalisches Institut, Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
⁶ Service d'Aéronomie du CNRS, BP 3, 91371 Verrières-le-Buisson, France
⁷ European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁸ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, 414 rue de la piscine, 38400 Saint Martin d'Hères, France

Received: 25 August 2004
Accepted: 10 September 2004

Abstract

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 14  (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.