The search for life in the universe will be a central item in the scientific activity of the 21st century. The TOPS report states: "Much of religion and philosophy has focused on attempts to understand how we and our world came to be". We "ask about the prevalence of planetary systems throughout the universe (...) and the likelihood that other planets have given birth to life, even advanced and intelligent forms of lives. We live in a remarkable time, when human beings (...) have attained the possibility of finding the first real answers to some of these most meaningful questions".

We revisit the idea by R. Bracewell and R. Angel to detect exo-planets around nearby stars in the IR (6-17 µm) and analyze their spectra, searching for H₂O, CO₂, CH₄, NH₃ and O₃ spectral features. The presence / absence of CO₂ would be the indication of a deep similarity / difference with Solar telluric planet atmospheres. The presence of H₂O would indicate a habitable planet and O₃ reveal a large photosynthesis activity, indicating the presence of carbon chemistry based life. In agreement with these authors, we suggest a IR nulling interferometer pointing to the star and working as a coronograph. Our main contribution is to propose an observatory made of 4 to 5 one meter class telescopes observing from 4 AU to avoid the Solar Zodiacal Light (ZL) background at 10 mm instead of eight meter ones observing from the Earth vicinity. This allows the mission to be feasible in the near future. The concept, named DARWIN, is under consideration by the European Space Agency for its Horizon 2000 Plus program.