Could We Search for Primitive Life on Extrasolar Planets in the Near Future?

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We revisit the idea of R. Bracewell and R. Angelet al.,that exoplanets around nearby stars could be detected in the IR (6–17 μm) and their spectra analyzed, searching for CO2, H2O, O3, CH4, and NH3spectral features. The presence, or absence, of CO2would be the indication of a deep similarity, or difference, with the atmospheres of telluric planets in the Solar System. That of H2O would indicate a habitable planet and O3would reveal a large photosynthetic activity, indicating the presence of life based on carbon chemistry. As do these authors, we suggest an IR nulling interferometer pointing to the star and working as a coronograph. Our main contribution is to propose an observatory made of four to five 1-m class telescopes observing from 4–5 AU to avoid the solar zodiacal light (ZL) background at 10 μm instead of four 8-m telescopes observing from the vicinity of Earth. This allows the mission to be feasible in thenear future. The discovery of ozone on an extrasolar planet would be a major scientific event. The concept, named DARWIN, is under consideration by the European Space Agency for its Horizon 2000 Plus program.