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The Search for Alien Polluters

By David Reneke

Astronomers search for alien air pollution, and Earth-based lasers could zap space junk.

We are on the threshold of “sniffing out” signs of alien life on other worlds. By studying exoplanet atmospheres, we can look for gases like oxygen and methane that only coexist if replenished by life. While these gases come from simple life forms like microbes, would advanced civilisations leave any detectable signs?

They might if they spew industrial pollution into the atmosphere. According to the Harvard Smithsonian Centre for Astrophysics, we could spot the fingerprints of certain pollutants under ideal conditions.“Human beings consider industrial pollution as a sign of intelligent life, but perhaps civilisations more advanced than us... will consider pollution as a sign of unintelligent life since it’s not smart to contaminate your own air,” says lead researcher Henry Lin.

The forthcoming James Webb Space Telescope should be able to detect chlorofluorocarbons (CFCs) at atmospheric levels ten times those on Earth – but only on an Earth-like planet circling a white dwarf star, which is what remains when a star like our Sun dies. The same scenario on an Earth-like planet orbiting a Sun-like star would require an instrument beyond JWST’s capabilities. However, a white dwarf still holds promise because recent observations are finding planets in similar environments.

While searching for CFCs could ferret out an existing alien civilisation, it could also detect the remnants of a civilisation that annihilated itself. Some pollutants last for 50,000 years in the Earth’s atmosphere while others last only 10 years. Detecting molecules from the long-lived category but none in the short-lived category would show that the sources are gone.

In that case, we could speculate that the aliens wised up and cleaned up their act. Or it would serve as a warning sign of the dangers of not being good stewards of our own planet.

Earth-based Lasers to Zap Space Junk
NASA scientists have suggested that Earth-based lasers could be used to nudge dangerous space junk away from satellites and spacecraft.

Space debris is typically moving at about 27,000 km/h. To put this in perspective, a 30 gram piece of debris travelling at this velocity has about the same kinetic energy as a large car travelling at 100 km/h.

The problem that debris poses gets worse when collisions spawn even more debris, eventually cluttering space with high-speed shrapnel. The February 2009 collision between an active Iridium communications satellite and a defunct Russian Cosmos weather satellite was the first example of the catastrophic destruction of an active satellite by an accidental collision.

A number of proposals have been floated to help clean up this garbage, such as rendezvousing with large objects like rocket bodies and propelling them back at Earth. However, such missions would be complex and expensive.

Instead of going up into space to bring down garbage, scientists have suggested remaining on the ground and zapping it with lasers.

A 1996 NASA study dubbed Project ORION proposed using powerful beams to vapourise surface material on targets, providing enough recoil to drive it earthward. The problem, of course, is that such lasers could be interpreted as weapons threatening other space-faring nations.

Now scientists at NASA’s Ames Centre have suggested using much less powerful and far cheaper lasers that can push debris without damaging it. Light can exert a force on matter, so researchers suggest that a commercially available laser with a 5–10 kW beam constantly focused on a piece of debris could work.

This is a unique approach to the problem. Previous work has focused on removing debris, but what’s being suggested here is simply to prevent collisions, allowing the debris to continue to decay in their orbits naturally due to atmospheric drag.

The scientists note that this system could be used to give a nudge to more than just garbage. They could push specially designed satellites, helping them save the weight of propellant.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com