Finding life in space by looking for extraterrestrial pollution

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Artist conception of James Webb Space Telescope

Credit: NASA

Harvard-Smithsonian Center for Astrophysics research looks for pollution fingerprints in space

If what we know as advanced life exists anywhere other than Earth, then perhaps they are dirtying their atmosphere as much as we have and that we could use such pollution components to perhaps more easily spot such planets in the universe.

 That’s the basics of new research put for this week by researchers at the Harvard-Smithsonian Center for Astrophysics that stated if we could spot the fingerprints of certain pollutants under ideal conditions, it would offer a new approach in the search for extraterrestrial intelligence.

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The researchers pointed specifically to the future James Webb Space Telescope should be able to detect two kinds of chlorofluorocarbons (CFCs) -- ozone-destroying chemicals used in solvents and aerosols. They calculated that that the James Webb could tease out the signal of CFCs if atmospheric levels were 10 times those on Earth. A particularly advanced civilization might intentionally pollute the atmosphere to high levels and globally warm a planet that is otherwise too cold for life.

 "We consider industrial pollution as a sign of intelligent life, 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," said Harvard student and lead author of the paper “Detecting industrial pollution in the atmospheres of Earth-like exoplanets” Henry Lin, in a statement.

 From the paper: “Detecting biosignatures, such as molecular oxygen in combination with a reducing gas, in the atmospheres of transiting exoplanets has been a major focus in the search for alien life. We point out that in addition to these generic indicators, anthropogenic pollution could be used as a novel biosignature for intelligent life. To this end, we identify pollutants in the Earth's atmosphere that have significant absorption features in the spectral range covered by the James Webb Space Telescope. We focus on tetrafluoromethane CF4 and trichlorofluoromethane, which are the easiest to detect chlorofluorocarbons produced by anthropogenic activity.”

"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," stated Harvard co-author Avi Loeb.

 According to Lin and Loeb, while searching for CFCs could ferret out an existing alien civilization, it also could detect the remnants of a civilization that annihilated itself. Some pollutants last for 50,000 years in 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, they stated.

 The researchers note that there is a limitation to using the Webb telescope in that it can only detect pollutants on an Earth-like planet circling a white dwarf star, which is what remains when a star like our Sun dies. That scenario would maximize the atmospheric signal. Finding pollution on an Earth-like planet orbiting a Sun-like star would require an instrument beyond JWST -- a next-next-generation telescope, the researchers stated.

 However the researchers note that a white dwarf star might be a better place to look for life than previously thought, since recent observations found planets in similar environments.

 Another caveat may be the Webb telescope. The $6.5 billion Webb telescope is the successor to the highly successful Hubble space telescope and according to NASA will be the most sensitive infrared space telescope ever built.

 It is designed to see the farthest galaxies in the universe and the light of the first stars; study young planetary systems; and look for conditions suitable for life on planets around other stars. The telescope features a large mirror, a little over 21-feet in diameter and a sunshield the size of a tennis court. The system would reside in an orbit about 1 million miles from the Earth.

 The project has been plagued by design issues and funding problems and routinely gets Congressional scrutiny over costs. The Webb is slated to be launched in 2018.

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