COULD WE SEARCH FOR PRIMITIVE LIFE ON EXTRASOLAR PLANETS IN THE NEAR FUTURE - THE DARWIN PROJECT

We revisit the idea of R, Bracewell and R. Angel et al., that exoplane ts around nearby stars could be detected in the IR (6-17 mu m) and the ir spectra analyzed, searching for CO2, H2O, O-3, CH4, and NH3 spectra l features, The presence, or absence, of CO2 would be the indication o f a deep similarity, or difference, with the atmospheres of telluric p lanets in the Solar System, That of H2O would indicate a habitable pla net and O-3 would reveal a large photosynthetic activity, indicating t he 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 avo id the solar zodiacal light (ZL) background at 10 mu m instead of four 8-m telescopes observing from the vicinity of Earth, This allows the mission to be feasible in the near future, The discovery of ozone on a n extrasolar planet would be a major scientific event, The concept, na med DARWIN, is under consideration by the European Space Agency for it s Horizon 2000 Plus program. (C) 1996 Academic Press, Inc.