Abstract
The recent detection of several planets in other solar systems has revived the discussion about possibilities of extraterrestrial life and of ways of a remote detection. According to our present understanding of the development of life on Earth and the basics of a water-carbon based system, there are several environmental requirements for the development of life. These conditions, however, are necessary but not sufficient indicators for the presence of life on other planets. On Earth, early life forms had a great impact on compositional changes of the terrestrial atmosphere by the production and continued supply of free oxygen. This paper discusses spectral features of oxygen emission and absorption and the possibilities of their use for a remote characterization of the chemical composition of extraterrestrial atmospheres. Observations of planets and moons in the solar system indicate, that oxygen emissions can be produced by many processes and that only a complete characterization of an atmosphere and the detection of significant amounts of molecular oxygen can be used as an indicator for the possible existence of higher life forms.
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