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MODERN TIMES Art Hobson [email protected] NWA Times 15 August 2009 On the trail of life in the universe For at least 2000 years, humankind has speculated on the question "Are we alone?" In the first century BCE, the Roman poet and philosopher Lucretius suggested that, just as life originated by blind, spontaneous chemical interactions on Earth, "we must acknowledge that such combinations of other atoms happen elsewhere in the universe to make worlds such as this one …with races of different men and different animals." I expect we will discover extraterrestrial life within 15 years, although it's highly unlikely to involve intelligent life and will probably be single-celled microbial life, like simple algae or bacteria. It will be a landmark in human history. You live in the heroic age of exoplanet (planets around stars other than the sun) discovery. Since all other stars can be seen only as a single point of light, even the discovery of a single such planet is an awsome feat. The first exoplanet was discovered in 1995, and 340 are now known. Encouragingly for those of us who would be thrilled to find that the universe is filled with life, most of the discovered planets lie in their star's "habitable zone" within which the star's radiation has an intensity similar to the intensity of sunlight on Earth. So these planets are candidates for having water in the liquid state rather than as steam or ice. Life on Earth came from the oceans and is still made mostly of water. Laboratory experiments suggest that, given an Earth-sized rocky planet plus water, life is highly likely to develop through natural chemical processes. This is probably how life developed on Earth. To date, astronomers have discovered most exoplanets by detecting a star's subtle wobbling in response to an orbiting planet. A star that wobbles sends out light whose spectrum (or colors) wobble first toward violet and then toward red, for the same reason (known as the Doppler effect) that an ambulance's siren wobbles toward higher and then toward lower pitches as it approaches and then recedes from you. Most such discoveries have been of large, Jupiter-like planets, because high-mass planets cause big wobbles of the central star and so are easiest to detect. These large planets are not so likely to harbor life. But the discoveries indicate that the actual number of (mostly still undetected) planets rises steeply with decreasing planet mass, making Earth-like planets highly likely. Most known exoplanets orbit sun-like stars and smaller, cooler stars known as "red dwarfs." Red dwarfs seem more likely than sun-like stars to be hosts for life, since they comprise 80 percent of the stars near Earth and they give off their dim red light steadily for far longer than our sun's 10-billion year lifetime (of which 5 billion years have now passed). Massachusetts Institute of Technology astronomer Sara Seeger thinks that "infrared astronomy," based on invisible light whose wavelength is a little longer than visible light's wavelength, might find signs of life around a red dwarf within a few years. A second method for detecting exoplanets concentrates only on those planets that happen to orbit their star in such a way as to cross directly in front of the star as seen from Earth. These "transiting" planets, while they are in front of their star, reveal their presence by temporarily reducing slightly the light arriving at Earth from the star. Careful monitoring of the reduced starlight, combined with information from the star's Doppler effect, tells astronomers both the radius and mass of the exoplanet and can reveal small rocky planets similar to ours. Sixty transiting planets are known to date. A space-based transit survey by the European Space Agency's Corot satellite has detected planets as small as two Earth diameters. NASA's Kepler mission, launched this past March and named for the great German astronomer who deciphered our solar (sun) system's architecture, will monitor 100,000 sun-like stars. About 1 percent of these stars are expected to have transiting Earth-like planets in their star's habitable zone. A third method is the most technically difficult but offers the greatest prospect for revealing life. It is the direct detection of an exoplanet's light--directly seeing the planet. It's not easy to detect a planet's dim light in the many billion times more intense glare of light from the planet's nearby star. To combat this glare, astronomers must place a screen either inside or outside their telescope to block the star's light while allowing the planet's light to enter the telescope. This method will be perfected before long and can, by studying the precise frequencies (or colors) of light from the planet, reveal the chemical signs of life. The prospects are anybody's guess, but most of us who love to ponder this question think that astronomers will find evidence that single-celled microbial life exists around millions to billions of stars in our Milky Way galaxy alone. Because our galaxy is only a tiny part of the universe, this would mean that the number of instances of life in the universe is unimaginably large. But the prospects for complex multi-cellular life are far more dim. And the prospects for intelligent life are dimmer still. Here's one of the reasons why: Judging from Earth's history, intelligent life requires billions of years of evolution. Animal instincts develop during this period, and these primitive instincts can be destructive in intelligent lifeforms unless they are rationally controlled. Judging from humankind's destruction of our own environment, our superstitious belief systems, and our uncontrolled violence, the prospects for such rational control here and on other planets are not promising. Thus there might be few if any surviving intelligent civilizations out there.