* Corresponding authors

^a Department of Astronomy, University of Maryland, College Park, MD, USA
E-mail: conor.a.nixon@nasa.gov
Fax: (+1) 301 286-0212
Tel: (+1) 301 286-6757

^b Planetary Systems Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA

^c Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK

^d LISA, CNRS, UMR 7583, Universités Paris 7 et Paris Est, 61 Avenue Général de Gaulle, Créteil, France

^e Department of Physics, College of Biological and Physical Sciences, University of Nairobi, P.O. Box 30197, Nairobi, Kenya

^f Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

^g Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, USA

^h LESIA, Observatoire de Paris-Meudon, Meudon Principal Cedex, France

ⁱ Department of Space Science, Cornell University, Ithaca, NY, USA

^j Adnet Systems, Inc., Rockville, MD, USA