A test for the search for life on extrasolar planets: Looking for the terrestrial vegetation signature in the Earthshine spectrum

摘要

We report spectroscopic observations (400 to 800nm, R = approx 100) ofEarthshine in June, July and October 2001 from which normalised Earth albedospectra have been derived. The resulting spectra clearly show the blue colourof the Earth due to Rayleigh diffusion in its atmosphere. They also show thesignatures of oxygen, ozone and water vapour. We tried to extract from thesespectra the signature of Earth vegetation. A variable signal (4 to 10 +/-3%)around 700nm has been measured in the Earth albedo. It is interpreted as beingdue to the vegetation red edge, expected to be between 2 to 10% of the Earthalbedo at 700nm, depending on models. We discuss the primary goal of thepresent observations: their application to the detection of vegetation-likebiosignatures on extrasolar planets.