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Project Progress

In this project VPL team members explore the nature and detectability of biosignatures, global signs of life in the atmosphere or on the surface of a planet.

The most robust biosignature gases for a photosynthetic biosphere are oxygen (O₂) and ozone (O₃). These are thought to be especially strong biosignatures when either is detected in conjunction with methane (CH₄).This year we submitted work on the potential non-biological generation of oxygen and ozone, which could result in a “false positive” for life (Domagal-Goldman et al., 2012). Using coupled climate-photochemical models we show that potentially detectable concentrations of O₃ can be produced on lifeless terrestrial planets orbiting M dwarf stars, due to slower photochemical destruction of O₃. Thus, detection of O₃ and CH₄ in the atmosphere of a planet orbiting a relatively cool star is not sufficient proof for a biosphere. Instead, discrimination between O₃ sources must be made by analyzing the stellar and atmospheric context of the O₃. Specifically, understanding the spectral characteristics of the stellar UV spectrum, and obtaining planetary spectra in the UV, visible, and IR should allow progressively more robust identification of this false positive for life.

In parallel, we worked with simulators for three different Terrestrial Planet Finder architectures, namely coronograph, interferometer and occulter telescopes that will one day be able to observe and determine the properties of extrasolar terrestrial planets. I cross-comparison of the detectability of known biosignatures and habitability markers for the three architectures is currently in preparation (Evans et al., 2013).