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Researchers ask 'Do aliens use hairspray?'

Hi-tech planets If you want to find advanced alien civilisations in the universe, look for their greenhouse gas emissions, according to a team of US scientists.

Astrophysicist Dr Sanjoy Som is president of the Blue Marble Space Institute of Science, which is looking at developing computer models of exoplanet atmospheres. In particular, they are interested in simulating planets with a 'techno-signature'.

"A bio-signature can be an indicator of life, whereas a techno-signature is an indicator of industrialised life," says Som .

One such techno-signature is chlorofluorocarbon (CFC), which was once widely used as an aerosol propellant and refrigerant. The compound acts as a greenhouse gas and destroys the ozone layer. Despite being phased out in the early 1990s, CFCs are long-lasting and expected to persist in the Earth's atmosphere until the end of this century.

"CFCs are entirely artificial and cannot be produced naturally," he says. "If such a greenhouse gas was detected than it would be a strong hint for the presence of an industrialised life form."

The models developed by researchers will simulate what a distant exoplanet with CFCs in its atmosphere would look like from Earth.

Som says current telescopes can at best only detect "first-order" gases - that is gases in high abundance such as hydrogen - in the atmospheres of exoplanets.

"We don't yet have the technology to measure in detail the composition of atmospheres of exoplanets, but once we do it would be nice to have something to compare it to," he says.

Som says the detection of CFCs and other artificial greenhouse gases may provide clues as to how advanced a planet's civilisation is.

"If you find a planet that is right on the edge of a habitable zone and you find it has a lot of greenhouse gases in it, chances are that planet is being actively terraformed."

To fund the project the researchers have turned to the internet, setting up a page on the crowd-source funding Petridish.org, a website specifically developed for science research projects.

Som hopes this funding model, if successful, will allow scientists to conduct research without having to be attached to a university or research body, as well as provide extra incentive to communicate their results.

What are the chances of finding CFC-producing aliens on other worlds? Som is reluctant to say, but he suspects there is life out there.

"It's fascinating to think that we are not alone, not only for scientific reasons, but also for philosophical reasons. If we do find life elsewhere it would cause a complete reassessment of what it means to be a human being."