EXO-/ASTROBIOLOGY WITH A DARWIN/TPF MISSION

摘要

The spectroscopic characterization of Earth-like ex-oplanets is one of the goals shared by two major projects: Darwin (ESA) and TPF-Terrestrial Planet Finder (NASA). By producing low resolution spectra of the planetary thermal emission, they will be able to detect the 9.6 μm band of O_3 which may be the signature of an O_2-rich atmosphere sustained by a biological activity. In this paper, we review several studies focusing on the possible use of this ozone signature as a biomarker for terrestrial exoplanets. First, we stress the risk of false positive detection produced by abiotic photochemical production of O_2 and O_3 and we show how to filter these imposters out by selecting only the simultaneous detection of O_3-CO_2-H_2O (triple signature). In a second part, we investigate the false, negative, cases: when O_2-rich atmospheres do not exhibit the O_3 feature. This happens when the partial pressure of CO_2 is too high or, unexpectedly, when the O_3 layer is too dense. Eventually, we present other eventual biomarkers that could trace life where O_3 fails.