1. UNESP, Universidade EstadualPaulista, Grupo de Dinâmica Orbital e Planetologia, Guaratinguetá, CEP 12516-410, SP, Brazil
2. Department of Earth, Environmental and Planetary Sciences, MS 126, Rice University, Houston, TX 77005, USA
3. Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, F-33615 Pessac, France
4. Max-Planck-Institut für Astronomie, K”onigstuhl 17, D-69117 Heidelberg, Germany