[1] Royal Observ Belgium, Dept Reference Syst & Planetol, B-1180 Brussels, Belgium
[2] Univ Roma Tor Vergata, Lab Astrobiol & Mol Biol Cyanobacteria, I-00133 Rome, Italy
[3] GFZ German Res Ctr Geosci, D-14473 Potsdam, Germany
[4] Univ Bristol, Sch Geog Sci, Bristol BS8 1SS, Avon, England
[5] Univ Glasgow, Sch Geog & Earth Sci, Glasgow G12 8QQ, Lanark, Scotland
[6] Univ Edinburgh, Sch Phys & Astron, Edinburgh EH9 3FD, Midlothian, Scotland
[7] INAF Astrophys Observ Arcetri, I-50124 Florence, Italy