1. 1Globe Institute, University of Copenhagen, 1350 Copenhagen, Denmark
2. 2Department of Geosciences, Swedish Museum of Natural History, 114 18 Stockholm, Sweden
3. 3Department of Physical Sciences, Kingsborough Community College, City University of New York, Brooklyn, New York 11235, USA
4. 4Cryospheric Sciences Laboratory, National Aeronautics and Space Administration (NASA) Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
5. 5Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), CNRS, Université Grenoble Alpes, 38058 Grenoble Cédex 9, France