Department of Applied Geophysics, Charles Universtiy in Prague, Albertov 6, Prague, 12843, Czech Republic; Department of Physics, University of Helsinki, P. O. Box 64, Helsinki, 00014, Finland
Department of Physics, University of Helsinki, P. O. Box 64, Helsinki, 00014, Finland
Institut für Planetologie, Universität Münster, Münster, 48149, Germany