Want to Find ET? Look for Air Pollution

— -- After trying unsuccessfully for several decades to eavesdrop on radio signals from outer space, scientists are looking at a new way to find evidence of intelligent life elsewhere in the universe.

Never mind trying to hear an alien production of "I Love Lucy." Instead, look for signs of air pollution.

No kidding.

The theory goes like this: Like humans, ET would probably try to harness every source of energy on the planet to build a better life with technological advantages like automatic dish washers and smart phones. That would almost surely result in a heavily polluted atmosphere that might be detectable from Earth.

The idea has been around awhile, but the discussion has centered on the typical byproducts of fossil fuel consumption -- carbon dioxide and methane gas. But these can be produced by microbes, so instead of finding ET, we might just find a pile of slime.

Progress, but not exactly what most of us had in mind.

Researchers at Harvard College and the Harvard-Smithsonian Center for Astrophysics have suggested a way to zero in on ET himself. Don't look for atmospheric chemicals that a bunch of bugs could make. Look for chemicals that could only be produced by an industrial society.

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One likely target would be chlorofluorocarbons (CFCs), the human-made compounds that were destroying the earth's ozone and which were banned by much of the world several years ago. These compounds were primarily used for refrigeration and as solvents, and if they exist in another planet's atmosphere, they must have been invented by an industrialized society.

However, the inevitable result would be air pollution, so maybe what we are really looking for is a sign of "unintelligent life," Harvard physicist Henry Lin, lead author of a study to be published in The Astrophysical Journal, said in a telephone interview.

Lin and colleagues Gonzalo Gonzalez Abad and Abraham Loeb are serious about their proposal, although Lin agreed that it's a long shot, and nothing on the planet today could carry out the research to see if they are on the right track. But the James Webb Space Telescope, scheduled for launching in 2018, might be able to pull it off.

The researchers contend the logical place to start would be with stars called white dwarfs, which are nearing the end of their lives. White dwarfs are in a cooling phase, and as they burn their resources they shrink, so "a white dwarf roughly the same temperature as the sun would be about the size of the Earth," Lin said.

Although many scientists believe white dwarfs probably have planets, none have been found so far. A planet about the size of the Earth, circling a white dwarf of nearly the same size, would be an ideal target for a telescope designed to analyze the chemical composition of anything in its sight, including the atmosphere of distant planets.

Since both bodies are the same size, "a larger fraction of the starlight from the white dwarf gets filtered by the atmosphere" of the planet as it passes between the star and the telescope, Lin said. How the starlight is refracted by chemical compounds in the atmosphere would reveal what is in the planet's air.

So a white dwarf would produce a "much, much better signal," greatly increasing the odds that CFCs could be found, he added.

Sounds promising, but Lin readily agrees it's no slam dunk.

The transit of the planet past the dwarf would be relatively brief, so the telescope could observe a promising target only about five minutes per day. And the pollution level would have to be at least 10 times as bad as on Earth to be observable. Also, competition for time on the next generation space telescope will be fierce.

But any advanced society would eventually discover the downside of pollution, and since CFCs only last in the atmosphere for a few decades, the "window of opportunity is very brief," Lin said.

The researchers point out that what we may well discover is the remnants of an industrial society that poisoned its planet, leading to its own demise. Even a cat knows better than to mess in its own house.

If things got even worse, and conflicting societies on a distant planet blew themselves up, we might find space junk orbiting another star that clearly was produced by folks who didn't see the end coming.

There's another scenario that fits neatly with all of this. Suppose the chemicals were deliberately launched into the atmosphere of a planet that was growing colder because of a cooling star? In that case, the evidence might persist for millions of years, not just a century or so, and the concentration of chemicals might be much greater.

That's not as farfetched as it sounds.

For decades now, one of the nation's leading theoretical physicists, Freeman Dyson, has promoted an idea that sounds disturbingly like the current situation on planet Earth.

In 1960 Dyson speculated that any technological civilization would constantly increase its lust for more energy, and eventually the finite sources would become depleted. The only way to meet the demand would be to trap more energy from the sun.

He suggested a series of orbiting structures that could capture every ray of sunlight, a vision that became known as the Dyson Sphere.

It was a bold idea, and although Dyson has himself admitted he first came across the idea in a 1937 science fiction novel, others have expanded the concept to such silly lengths that last year he said he regretted the fact that his name has been linked to it.

But what about a distant planet where a deadly chill is setting in, and the only way to survive is by pumping gases into the atmosphere to warm it up? Maybe what we are looking for is a real-life Dyson Sphere.