Energy Sources for, and Detectability of, Life on Extrasolar Planets
Life in the accessible biosphere on Earth today is energised in primary productivity mainly by solar radiation through photolithotrophy with a minor role for chemolithotrophy based on reductants from hydrothermal vents and volcanoes, as well as reductant from photolithotrophy (Johnston et al., 2009; Raven, 2009a). Food webs downstream of primary producers involve chemo-organotrophs which regenerate chemical resources for photolithotrophy and chemolithotrophy. In addition to these energy sources for growth and maintenance, there are also a range of other potential energy sources for growth and maintenance of organisms (Muller and Schulze-Makuch, 2006), with varying extents of experimental support for their occurrence. The analysis of these alternative energy sources involves not only the likelihood of their occurrence when the energy source is available but also the availability of these energy sources on Earth. These analyses permit estimates of how globally significant the alternative energy sources could be. In the context of astrobiology, we review and extend previous attempts to quantify the possible extent of photolithotrophy and chemolithotrophy, and of the alternative energy sources, as well as the possibilities of remote sensing of these processes on Earth.
KeywordsHydrothermal Vent Sulphide Oxidation Alternative Energy Source Oxygenic Photosynthesis Extrasolar Planet
The University of Dundee is a registered Scottish Charity, No. SC 010596.
L. Kaltenegger acknowledges the support of the Harvard Origins of Life Initiative and the NASA Astrobiology Institute.
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