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The Astrophysical Context of Life
research with other disciplines. NAI teams, in particular, should make an explicit effort to promote joint research between astronomers and researchers in other disciplines. Evidence for this would consist of astronomers writing papers with biologists or geologists or at least citing that literature (and vice versa) and dual degree programs.
Recommendation: The committee recommends that NASA develop metrics to evaluate the degree to which truly interdisciplinary work involving astronomy and astrophysics is being done in the current NAI nodes.
The Terrestrial Planet Finder (TPF)2 mission and Darwin,3 the parallel program of the European Space Agency, will search for terrestrial planets and attempt to detect evidence of life. The successful planning and execution of the NASA TPF mission will require a great deal of interdisciplinary input from astrobiologists working with astrophysicist colleagues. As a specific example, stellar astrophysicists viewing their research objects through the lenses of astrobiology must now try to understand potential TPF target stars as the astrophysical environment and energy source for potential life-sustaining planets, not just as stars.
TPF will require the attention of the astronomical community in at least three ways: work on improving star lists; work on improving predicted signals from various types of planets in various evolutionary or temporary states; and work on developing techniques and concepts for planet detection and characterization. The astronomical context will be important to learn about the atmospheric lifetime or practical detectability of a biomarker in a given astrophysical environment—that is, the scenario under which TPF will operate. Biosignatures can be generated in part by radiation from the parent star, as happens when ozone is generated from molecular oxygen. Biomarkers are also detectable in either stellar reflected light in the visible or as a function of planetary atmospheric temperature structure in the mid-infrared. (This planetary temperature structure is also a function of chemical composition of the atmosphere, all of which—chemical composition and temperature structure—is driven by the spectral energy distribution and variability of the host star.) The astronomical perspective forces us to consider the nature and detectability of biosignatures for host stars that are unlike our own Sun, and it requires strong interdisciplinary collaboration between stellar astronomers, planetary atmospheric physicists, atmospheric chemists, and spectroscopists.
The specific point that large departures from equilibrium are likely to be driven by biological processes was made by Lovelock.4 It is based on the idea that enzymes are highly selective, whereas inorganic catalysts are not. Thus we may identify a biomarker long before we identify the process that gave rise to it. The Astrobiology Roadmap also notes as follows: “A strategy is needed for recognizing novel biosignatures. This strategy ultimately should accommodate a diversity of habitable conditions, biota and technologies in the universe that probably exceeds the diversity observed on Earth.” The opportunity for interdisciplinary work in these areas is great.
At least two teams in NAI (VPL and UA) are already working on TPF-related problems; however, the main resources associated with the mission(s) come from mission funds, not astrobiology resources.