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Astronomers take on a new tactic for finding ET: look for alien polluters

The brown haze in the atmosphere of this polluted alien could contain chemicals detectible to the next generation of space telescopes, revealing the presence of an alien civilization. Credit: Christine Pulliam (CfA)

The brown haze in the atmosphere of this polluted alien could contain chemicals detectible to the next generation of space telescopes, revealing the presence of an alien civilization. Credit: Christine Pulliam (CfA)

Scott Sutherland
Meteorologist/Science Writer

Thursday, July 24, 2014, 4:39 PM - In the search for advanced alien civilizations, perhaps we're going about things the wrong way. Rather than looking for the good, like communication signals and technological marvels, we should be looking for the bad stuff.

There are a few ways that aliens would be able to tell that Earth is populated by an advanced species. If they were in orbit, the abundant orbiting satellites, junk and debris would be one thing giving us away, not to mention our city lights dotting the dark side of the planet. Local space is saturated with radio and television signals, announcing our presence to anyone within about 100 light years of Earth. For aliens further away, they might be able to detect the oxygen and methane in our atmosphere using telescopes, but that would just give them a clue that life exists here, not necessarily intelligent life. However, a sure-fire method might be to look for gases that don't support life, or that aren't produced directly by forms of life, but instead look for stuff produced by their activities - like industrial pollution.

That's the focus of a new study by a trio of astronomers from Harvard and the Harvard-Smithsonian Center for Astrophysics - Henry Lin, Avi Loeb and Gonzalo Gonzalez Abad. They're turning this idea around, and planning on using the new James Webb Space Telescope (JWST) - slated for launch in 2018 - to search the atmospheres of exoplanets for the polluting byproducts of alien civilizations. Specifically, according to the researchers, the telescope should be able to pick out ozone-destroying chlorofluorocarbons (CFCs) in the atmosphere of an alien world, and since these are chemicals not normally found in nature, finding them would be a fairly good indication that a technological civilization existed there. 

There are a few limitations to this kind of search. Firstly, the levels of CFCs in the alien atmosphere would have to be around 10 times greater than we have here on Earth. Second, they would have to restrict their search to planets orbiting around white dwarf stars - the remnant of a 'dead' Sun-like star. So, this would possibly only find alien species that were long gone (killed when their star ballooned into a red giant and then died), or it would find the most polluting aliens.

"People often refer to ETs as 'little green men,' but the ETs detectable by this method should not be labeled 'green' since they are environmentally unfriendly," Loeb said in a statement.

According to the CfA press release, a next-generation telescope, beyond the JWST, could look for other pollutants though, and find them on planets that were more likely to currently support life. Such a telescope might even be able to pick out shorter- vs longer-lived pollutants, thus possibly finding aliens that "wised up and cleaned up their act," as Loeb put it.

"Or in a darker scenario, it would serve as a warning sign of the dangers of not being good stewards of our own planet," he added.

When it comes down to it, while it's certainly a realistic way of searching for any fellow intelligent species out there, it's not exactly focusing on the most positive aspect of a civilization.

"We consider industrial pollution as a sign of intelligent life," said lead researcher Henry Lin, according to the CfA press release, "but perhaps civilizations more advanced than us, with their own SETI programs, will consider pollution as a sign of unintelligent life since it's not smart to contaminate your own air."

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