[1] Univ Chicago, Enrico Fermi Inst, Chicago, IL 60637 USA
[2] Univ Chicago, Origins Lab, Dept Geophys Sci, Chicago, IL 60637 USA
[3] CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA
[4] Univ Lille 1, Unite Mat & Transformat, F-59655 Villeneuve Dascq, France