1. Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA
2. CEA, DAM, DIF, Arpajon 91297, France
3. École Normale Supérieure de Lyon, Université Lyon 1, Laboratoire de Géologie de Lyon, CNRS UMR 5276, 69364 Lyon Cedex 07, France
4. Department of Astronomy, University of California, Berkeley, California 94720, USA