Transmission spectrum of Venus

This event is an unique opportunity to assess the feasibility of the atmospheric characterisation of Earth-size exoplanets near the habitable zone with the transmission spectroscopy technique and provide an invaluable proxy for the atmosphere of such a planet. In this letter, we provide a theoretical transmission spectrum of the atmosphere of Venus that could be tested with spectroscopic observations during the 2012 transit.

This is done using radiative transfer across Venus' atmosphere, with inputs from in-situ missions such as Venus Express and theoretical models. The transmission spectrum covers a range of 0.1-5m and probes the limb between 70 and 150km in altitude. It is dominated in UV by carbon dioxide absorption producing a broad transit signal of ~20ppm as seen from Earth, and from 0.2 to 2.7m by Mie extinction (~5ppm at 0.8m) caused by droplets of sulfuric acid composing an upper haze layer above the main deck of clouds.