[1] Univ Calif Berkeley, Dept Astron, Berkeley, CA 94720 USA
[2] SETI Inst, Mountain View, CA 94043 USA
[3] CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA
[4] Lawrence Livermore Natl Lab, Inst Geophys & Planetary Phys, Livermore, CA 94550 USA
[5] Univ Zagreb, Fac Sci, Zagreb 1000, Croatia