Caption: NASA engineer Ernie Wright looks on as the first six flight ready James Webb Space Telescope's primary mirror segments are prepped to begin final cryogenic testing at NASA's Marshall Space Flight Center. Credit: NASA/MSFC/David Higginbotham. Caption text copyright NASA.
So far, the search for extraterrestrial civilizations has focused on looking for electromagnetic radiation from target star systems, such as the by-products of internal communications or artificial lighting, including street lights.
However, a new paper published by the Astrophysical Journal entitled Detecting industrial pollution in the atmospheres of Earth-like exoplanets has thrown another idea into the mix: what if we searched for pollutants instead?
Henry Lin and his co-authors argue that anthropogenic pollution could be used as a biosignature for intelligent extraterrestrial life. Oxygen has long been regarded as an indicator of life, but why not go a step further and search for indicators of industrial activity? The main reason is that so far, this has been impossible.
But perhaps not for long.
In 2018, the James Webb Space Telescope will be launched to the great excitement of the international astronomical community. The Webb, a collaborative project by NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), and currently under development at the NASA Goddard Space Flight Center, will be the number one space observatory of the next decade, the go-to infra-red telescope that will serve astronomers around the world. What's crucial about the Webb, with regards to the paper by Lin et al., is that it will be capable of detecting CFCs in the atmospheres of distant worlds.
How to isolate an extrasolar planet's spectrum. Source: NASA JPL/Caltech
Key targets will include Earth-sized exoplanets orbiting white dwarfs, not only because they are likely to have long-lived habitable zones, but also because the contrast between the atmospheric transmission spectrum and the backdrop of space will be most conducive to the detection of pollutants. The easiest CFCs to detect, according to the study, will be tetrafluoromethane and trichlorofluoromethane, two molecules that are produced by advanced industrial processes. By targeting white dwarfs, stars that are smaller than our Sun, any Earth-sized planets transiting them will produce a larger imprint in the star's spectrum, which would aid the detection of pollutants.
This process could, in time, be advanced to include Sun-sized stars. In the meantime, however, the search for common-or-garden methane, and other organic species, in the atmospheres of extrasolar planets continues to give indications that life, simple or advanced, may well thrive in the universe.
