EXTREMELY LARGE TELESCOPES

biological processes – most notably photosynthesis. Moreover, because it reacts so readily with other molecules, oxygen has to be continuously replenished to remain in circulation. Our own planet clearly signals the presence of life by the fact oxygen accounts for almost 21% of the atmosphere.

The presence of oxygen in a planet’s atmosphere, however, is by no means evidence of complex life forms; it can be produced by single-celled organisms, like the cyanobacteria thought responsible for the initial oxygenation of Earth’s atmosphere some 2.3 billion years ago. Biomarkers for multi-celled organisms are more subtle. Whether such signatures might be detectable at interstellar distances is a hot topic in astrobiology. Some possibilities do exist: for example, the chlorophyll content. Vegetation produces a characteristic spectral profile. This so-called ‘vegetation red edge’ is already used to map our own planet’s resources from space.

How might we react to the unequivocal detection of rudimentary life beyond our planet? Whether life exists elsewhere in space is one of the biggest questions of our time. Even the discovery of single-celled organisms would have far-reaching implications. But the finding that really would be overwhelming is unequivocal evidence of an intelligent civilisation. The sociocultural impacts of such a discovery would be profound. Science, technology, ethics, politics and religion – all will undergo major shifts as we come to terms with a completely new perspective: we are not alone.

The way ELTS might reveal that knowledge is by finding so-called technomarkers. There are chemicals that can only be introduced into a planet’s atmosphere in significant amounts by industrial processes. They include well-known offenders such as chlorofluorocarbons. Eventually ELTS should allow us to detect these tell-tale pollutants in the atmospheres of distant planets. The irony is inescapable: extraterrestrial intelligence discovered because aliens were trashing their planet, just as we are trashing ours.

FRED WATSON is the former astronomer in charge of the Australian Astronomical Observatory. His books include Stargazer: The Life and Times of the Telescope and Star-craving Mad, Tales from a Travelling Astronomer.

IMAGES 01 M3 Engineering 02 University of Cardiff 03 Giant Magellan Telescope – GMTO Corporation 04 ESO / L. Calçada