Once we become more adept at detecting Earth-sized planets, how can we tell if they’re inhabited? Technologically sophisticated life might radiate radio waves into space, but what more simple life? Would the “biomarkers”–telltale signatures–of more simple life be? A European Space Agency press release says that astrobiologists are working at hard to determine what the telltale signatures, known as “biomarkers”, would be for non-intelligent life in preparation for ESA’s Darwin mission next decade. Just by breathing, we affect the composition of the Earth’s atmosphere, so an obvious first step is to look for similar effects on distant planets by analyzing their atmospheric composition via its spectrum. Darwin will look for oxygen (actually, it will detect the ozone form of oxygen) because oxygen is used by some life forms and produced as waste by others. Many scientists think that without life, all oxygen would disappear within just four million years, because it reacts so easily with other chemicals. It will also detect carbon dioxide, water, and, in certain cases, methane. Finding ozone, liquid water and carbon dioxide simultaneously would be a very strong indicator of life being present. Once Darwin completes its survey of the nearest several thousand star-planet systems and finds a living planet, the next phase will be to understand the nature of its life forms–which means searching for more specific biomarkers, such as chlorophyll or industrial pollution.

An earlier story on Sci-Fi Today reported that NASA also plans to search for Earth-like planets around other stars and analyze them for telltale signs of life via its Terrestrial Planet Finder. To prepare, they launched the Virtual Planetary Laboratory to simulate the environments and spectra of extrasolar planets, thus enabling them to predict what the biomarkers may look like.