A test for the search for life on extrasolar planets

Abstract

We report spectroscopic observations (400-800 nm, R ≈ 100) of Earthshine in June, July and October 2001 from which normalized Earth albedo spectra have been derived. The resulting spetra 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 ± 3%) 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.