2012 Annual Science Report
VPL at University of Washington Reporting | SEP 2011 – AUG 2012
Detectability of Biosignatures
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. This year we submitted for publication modeling work that explores the potential for non-biological generation of oxygen and ozone in early Earth-like atmospheres, which could result in a “false positives” for photosynthetic life. In parallel, we worked with three simulators for telescopes that will one day be able to observe and determine the properties of extrasolar terrestrial planets, and used these simulators to calculate the relative detectability of gases produced by life.
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).
PROJECT INVESTIGATORS:Victoria Meadows
PROJECT MEMBERS:Mark Claire
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Indirect and direct astronomical observations of extrasolar habitable planets.
Earth's early biosphere.
Biosignatures to be sought in nearby planetary systems