Remember chlorofluorocarbons, aka CFCs? The big, bad ozone-depleting pollutant 1) sticks around for tens of thousands of years and 2) is almost entirely man-made. That means if extraterrestrial life are anything like us, according to astrophysicists at Harvard, CFCs could be a key to finding aliens.
First, a quick primer on how we could even detect pollution on faraway planets. In a few years, NASA will be launching its powerful, new James Webb Space Telescope (JWST), which will capture starlight filtering through atmospheres of exoplanets. By comparing the spectrum of light before and after it goes through an atmosphere, astrophysicists can figure out the gases that make it up.
Usually, when scientists are looking for signs of life, they're looking for oxygen, a highly reactive molecule that only exists in Earth's atmosphere because photosynthesising plants and bacteria keep replenishing it. (There was, in fact, a time in Earth's history when there was very little oxygen in the air.) But if we want to zero in on intelligent life–not just plants and bacteria—maybe we should look for industrial pollution.
A trio of astrophysicists at Harvard have calculated that the JWST could indeed detect CFCs on a planet orbiting a white dwarf. Gases like methane and nitrous oxide, which are also indicative of but not exclusive to human (or alien) activity, would also be detectable.
That's all assuming aliens would be as destructive toward their planet as we are. Perhaps the most fascinating and sobering detail of all is that because CFCs last for up to 100,000 years, we could be detecting alien civilisations and their polluting legacy long after they're gone. [ArXiv via New Scientist]
Top image: A super-Earth-size exoplanet. NASA Ames/JPL-Caltech