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Volume 392, Number 1, September II 2002
Page(s) 231 - 237
Section Formation and evolution of planetary systems

A&A 392, 231-237 (2002)
DOI: 10.1051/0004-6361:20020933

A test for the search for life on extrasolar planets

Looking for the terrestrial vegetation signature in the Earthshine spectrum
L. Arnold1, S. Gillet2, O. Lardière2, P. Riaud2, 3 and J. Schneider3

1  Observatoire de Haute-Provence (OHP) CNRS, 04870 Saint-Michel-l'Observatoire, France
2  Laboratoire d'Interférométrie Stellaire et Exoplanétaire (LISE) CNRS, 04870 Saint-Michel-l'Observatoire, France
3  Observatoire de Paris-Meudon, 92195 Meudon Cedex, France

(Received 24 December 2001 / Accepted 6 May (2002) )

We report spectroscopic observations ( 400-800 nm, $R\approx100$) of Earthshine in June, July and October 2001 from which normalized Earth albedo spectra have been derived. The resulting spectra clearly show the blue colour of the Earth due to Rayleigh diffusion in its atmosphere. They also show the signatures of oxygen, ozone and water vapour. We tried to extract from these spectra the signature of Earth vegetation. A variable signal (4 to $10 \pm3\%$) around 700 nm has been measured in the Earth albedo. It is interpreted as being due to the vegetation red edge, expected to be between 2 to $10\%$ of the Earth albedo at 700 nm, depending on models. We discuss the primary goal of the present observations: their application to the detection of vegetation-like biosignatures on extrasolar planets.

Key words: astrobiology -- stars: planetary systems

Offprint request: L. Arnold,

© ESO 2002