Telling twins apart: exo-Earths and Venuses with transit spectroscopy J.K. Barstow, S. Aigrain, P.G.J. Irwin, S. Kendrew, L.N. Fletcher May 1, 2016 Cite DOI radiative transfer methods: data analysis planets and satellites: atmospheres Related Erratum: Transit spectroscopy with JWST: systematics, star-spots and stitching Transit spectroscopy with James Webb Space Telescope: systematics, starspots and stitching Clouds on the Hot Jupiter HD189733b: Constraints from the Reflection Spectrum Constraining the atmosphere of GJ 1214b using an optimal estimation technique On the potential of the EChO mission to characterize gas giant atmospheres