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Search For Intelligent Life

Voyager missions, Epsilon Eridani, constellation Cetus, Lick Observatory, Allen Telescope Array

Solar system exploration may detect extraterrestrial life in the solar system that is not advanced enough to communicate with Earth. However, astrobiologists have employed other strategies of searching for intelligent, technological life—strategies aimed at communicating with or detecting communication from other worlds.

The Pioneer and Voyager missions carried messages from Earth for their eventual journeys through interstellar space. Pioneer 10 and 11 were the first objects planned to leave the solar system and carried small metal plaques depicting male and female humans with a coded message identifying the time and place of spacecraft origin. A more ambitious message was placed aboard the Voyager 1 and 2 spacecraft as a kind of time capsule. Each carried a gold-plated copper disk recording of sounds and images portraying the diversity of life and culture on Earth—including a variety of natural sounds, musical selections, and spoken greetings in 55 languages. These messages are on their way to the stars as the spacecraft enter regions beyond our solar system.

Spacecraft are not the fastest or most efficient way to send messages out of the solar system, or for cultures on other planets to send messages to Earth. Radio waves travel at the speed of light and can be sent out in many different directions. Astrobiologists began searching the skies for radio signals from extraterrestrial life in 1960, in the first Search for Extraterrestrial Intelligence (SETI) experiment. Frank Drake used the National Radio Astronomy Observatory in Green Bank, West Virginia, to search for radio signals for four months in 1960. This attempt was named Project Ozma after the queen in American writer L. Frank Baum’s novels about the imaginary land of Oz.

Project Ozma focused on the stars Tau Ceti in the constellation Cetus and Epsilon Eridani in the constellation Eridanus, both about 11 light-years (about 106 trillion km, about 66 trillion miles) from Earth. Drake’s search lasted six hours a day from April to July 1960, using a 26 m (85 ft) radio telescope tuned to the wavelength of radiation that cold hydrogen gas in interstellar space emits (a frequency of 1420 megahertz). With the exception of an early false alarm caused by a secret military experiment, no signals were detected.

Project Ozma used just one single-channel receiver, but NASA eventually developed the capability to monitor millions of channels simultaneously. On October 12, 1992, NASA’s two-part SETI effort initiated observations with the All-Sky Survey, a survey of space using a 34 m (112 ft) diameter radio telescope in Goldstone, California, and the Targeted Search, which examined solar-type stars using the National Science Foundation's 305 m (1,000 ft) telescope in Arecibo, Puerto Rico. The government-funded project was not appreciated by some in the United States Congress, however, and was canceled in October 1993.

Despite that setback, the private SETI Institute took over the search for extraterrestrial signals. The institute conducted Project Phoenix during a nine-year period from 1995 to 2004, using some of the equipment developed for the canceled NASA search. Phoenix made a targeted search of more than 800 relatively nearby stars similar to our sun with radio telescopes located in New South Wales, Australia, as well as at Arecibo and at Green Bank. No signals identifiable as originating from intelligent life were detected.

Another approach to searching for signals is to “piggyback” a special receiver onto radio astronomy work being done for conventional scientific research. The SETI receiver does not interfere with the data being collected by the main radio telescope. Beginning with a project dubbed SERENDIP, a number of versions of this untargeted type of search have taken place.

SERENDIP IV conducted with the Arecibo dish collected a vast amount of data covering about 30 percent of the sky. The data need to be carefully analyzed to extract possible signals coming from an artificial source. To do this, a project called SETI@home was started by the Space Sciences Laboratory at the University of California at Berkeley. SETI@home has signed up millions of volunteers on the Internet to process parts of the data on their personal computers at home, using special software.

Under development is the Allen Telescope Array (ATA) radio telescope, planned for completion in 2010 in the form of 350 antennas located northeast of San Francisco. The ATA radio telescope complex, sponsored by Microsoft cofounder Paul Allen, will carry out regular radio astronomy as well as searches for extraterrestrial signals for SETI.

Another technique to detect other possible signals from extraterrestrial life is called Optical SETI, which searches for laser pulses instead of radio waves. Versions of Optical SETI are being carried out by Harvard University and the Columbus Observatory in Ohio, and have been conducted at California’s Lick Observatory and other locations, including Australia.

The detection of intelligent life elsewhere in the universe would be one of the most momentous events in human history, with profound scientific, philosophical, and even religious implications.

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