Atmospheric biosignatures as tools in search for life on exoplanets

The first exoplanet was discovered about 20 years ago. Until then speculations about Earth 2, 3 or 4 were nothing but science fiction. Thanks to the Kepler mission, which has made groundbreaking contributions to planet discovery, we now have a list of more than 3500 planet candidates of which 151 have been confirmed. Among the confirmed planets are planets with earth-like properties in terms of size and distance to their central star.

The discovery of exoplanets and solar systems in our galaxy has triggered the need for the development of methods to evaluate whether living organisms are present. Among the complementary approaches, approaches focusing on the study of the atmospheric gas composition have been in focus. In particular the search for gases that could be produced by organisms, as we know them from Earth, have attracted most attention. Among the gases, oxygen at high concentrations and far from its chemical equilibrium is the prime candidate. We have chosen a different approach that addresses the role of living matter on atmospheric processes such as cloud formation and precipitation.