The question “are we alone?” is perhaps older than civilization itself, but recent advances in technology have shifted speculation about extraterrestrial life from the domain of philosophy and into the realm of science. Steady improvements in the ability of telescopes to peer into the atmospheres of planets around other stars are enabling scientists to contemplate the ways that life could be detected across the vast reaches of space.
One new strategy for spotting telltale evidence of extraterrestrial life is to look for “technosignatures.”
It’s a twist on another approach to scanning space, which involves hunting for evidence of the simplest forms of life. For example, our own atmosphere is notable for the simultaneous presence of oxygen and methane. Together, these molecules would destroy one another through rapid chemical reactions, but they remain in Earth’s atmosphere because both methane and oxygen are continually produced by living things: plants, animals, and microorganisms. This interaction between life and the planet suggests just one possible “biosignature” that we might look for on other planets.
But now I and other researchers intend to look as well for signs of technology. After all, many geologists think that the effects of human technology on our environment will be preserved in the rock record, demarcating an epoch of planetary history when large-scale farming began, materials such as plastic arose, and nuclear testing became feasible. Other industrial activities have altered the chemical composition of our atmosphere, such as the depletion of ozone by chlorofluorocarbons or the acceleration of climate change from fossil fuel burning. The planet itself is encircled by orbiting satellites, along with a cloud of debris from the broken remnants of failed or decommissioned satellites. Changes like these all are indicative of a new phase in our planet’s evolution in which technology is expanding the biosphere.
And so, just as the history of life on Earth motivates the search for biosignatures, Earth’s trajectory as a planet with an emerging sphere of technology suggests an analogous search for “technosignatures” in other planetary systems. Detecting gases like chlorofluorocarbons on another planet would be strong evidence of extraterrestrial industry. An extraterrestrial satellite belt much thicker than ours could also be detectable. A planet that covers its surface with solar panels or builds large orbiting solar collectors could conceivably be detected with a large enough telescope. The challenge of how to best identify, categorize, and prioritize scenarios such as these remains an important problem in the emerging science of technosignatures.
As we think about possible trajectories for our own civilization, the emerging scientific effort to understand and search for technosignatures may also help us better understand our future.
Jacob Haqq-Misra is a research scientist with the Blue Marble Space Institute of Science. Follow him on Twitter @haqqmisra. He recently hosted a NASA-sponsored workshop about technosignatures; posters and talks are available at technoclimes.org.