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Ehrenreich David, Vidal-Madjar A., Widemann Thomas, Gronoff G., Tanga Paolo, Barthélemy Mathieu, Lilensten Jean, Lecavelier des Etangs Alain, Arnold Luc

Transmission spectrum of Venus as a transiting exoplanet

Astronomy and Astrophysics, 2012, vol. 537, pp. L2

Référence DOI : 10.1051/0004-6361/201118400
Référence ADS : 2012A&A...537L...2E

Résumé :

On 5-6 June 2012, Venus will be transiting the Sun for the last time before 2117. 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 0.1-5 mum and probes the limb between 70 and 150 km in altitude. It is dominated in UV by carbon dioxide absorption producing a broad transit signal of ~20 ppm as seen from Earth, and from 0.2 to 2.7 mum by Mie extinction (~5 ppm at 0.8 mum) caused by droplets of sulfuric acid composing an upper haze layer above the main deck of clouds. These features are not expected for a terrestrial exoplanet and could help discriminating an Earth-like habitable world from a cytherean planet.

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