In exoplanet science the term “bioindicator” refers to an indication (or “hint”) that life as we know it could be present – but in order to decide more definitively would require additional information.
The detection, e.g., of atmospheric methane in an exoplanetary atmosphere would constitute a bioindicator because additional information is needed in order to determine whether or not the source is biological. This, in the case of methane, can be tested, e.g., by comparing the ratio of its outgassing amount with other outgassed species such as H2 (see, e.g., Oze et al. 2012) and/or by determining the carbon isotope ratio (as discussed in the review of Etiope and Sherwood Lollar 2013). In contrast, the term “biosignature” refers to a robust signal that is strongly suggestive of life. For example, the atmospheric detection of an Earth-like amount of nitrous oxide (N2O) for an Earth-like planet orbiting a sunlike star would constitute a biosignature because according...
KeywordsIsotope Ratio Nitrous Oxide Carbon Isotope Carbon Isotope Ratio Atmospheric Methane
References and Further Reading
- Hewitt CN, Jackson AV (eds) (2009) Atmospheric science for environmental scientists. Wiley-Blackwell, Oxford, p 105Google Scholar