The two years previous to 1997 have produced some of the most exciting results in the history of astronomy: the indirect detection of planets beyond our solar system. The study of the characteristics and physical nature of exo-planets requires an infrared interferometer in space. Such observatory would directly detect the thermal emission from exo-planets and would allow us to see signatures of molecules, such as water, ozone and carbon dioxide, in their atmospheres. The presence of such molecules would be strong evidence for exo-life. In addition, this kind of instrument would help to...