1. Department of Physics, University of Warwick , Coventry CV4 7AL , UK
2. Centre for Exoplanets and Habitability, University of Warwick , Coventry CV4 7AL , UK
3. Department of Physics, University of Turin , Via Pietro Giuria 1, I-10125 Turin , Italy
4. Leiden Observatory, Leiden University , Postbus 9513, NL-2300 RA Leiden , the Netherlands
5. Department of Physics, University of Oxford , Keble Road, Oxford OX1 3RH , UK
6. Jet Propulsion Laboratory, California Institute of Technology , Pasadena, CA 91109 , USA