Everyone knows air pollution is bad for humans, but it might also be good for detecting alien life on distant planets, according to a recent study published on a preprint server.
We might detect air pollution from alien civilizations
Air pollution on Earth is visible from space — even beyond our solar system. If an alien civilization far from Earth took a peek at our planet, they would see a biosignature of civilization on Earth.
And, there's a chance we could do the same to them.
The recent study evaluates a single chemical pollutant stemming from both natural and human-made causes on Earth — NO2, or nitrogen dioxide. The nitrogen dioxide might serve as a technosignature on a life-supporting planet orbiting a star like the sun — and could be detected with a 49-ft (15-m) telescope.
CFCs more reliable signal of alien intelligence
This study marked the first time NO2 was fully evaluated as a potential "technosignature," or sign of technological manipulation of a planet's atmosphere.
"Other studies have examined Chlorofluorocarbons (CFCs) as possible technosignatures, which are industrial products that were widely used as refrigerants until they were phased out because of their role in ozone depletion," said Co-Author Jacob Haqq-Misra of the paper — from the Blue Marble Institute of Science in Seattle Washington, in a NASA press release. "CFCs are also a powerful greenhouse gas that could be used to terraform a planet like Mars by providing additional warming from the atmosphere. As far as we know, CFCs are not produced by biology at all, so they are a more obvious technosignature than NO2."
Future NASA telescopes may detect air pollution 30 light-years away
"However, CFCs are very specific manufactured chemicals that might not be prevalent elsewhere; NO2, by comparison, is a general byproduct of any combustion process," added Haqq-Misra in the press release.
The research team used computer modeling to predict whether nitrogen dioxide pollution could create a signal we could identify with present-day and forthcoming telescopes. NO2 absorbs some colors of visible light — which telescopes can detect from the light exoplanets reflect from their host star.
The team discovered how an Earth-like rocky planet in orbit around a sun-like star with a resident civilization could be detected up to roughly 30 light-years away — using 400 hours of observing time — provided one of NASA's future telescopes was looking at visible wavelengths.
Nitrogen dioxide could point to alien life
While this is a long observation period, it's doesn't stray far from the time it took NASA's Hubble Space Telescope to capture the renowned Deep Field images.
However, clouds and aerosols in an exoplanet's atmosphere could absorb wavelengths of life similar to those absorbed by a technologically-generated NO2 — mimicking the technosignature. But the team plans to apply a more developed model to see if this natural malleability can be compensated for.
It's the most exciting time to be alive for astronomers and other scientists involved in the search for signs of life beyond our solar system. But in possibly adding another means of detecting life to humanity's cosmic toolkit, we're one step closer to finding life like us that might be out there.