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Planetary News: Search for Life (2007)

SETI Researchers Propose Eavesdropping on Alien Civilizations

Click to enlarge > An artist's depiction of a distant planet inhabited by an alien civilization Credit: David A. Aguilar (CfA)

Ever since project Ozma first turned a radio-telescopic ear to the skies in 1960, dozens of SETI projects sought to find an intelligent signal from the stars. Some were targeted searches, focusing on the most promising nearby stars, while others were all-sky surveys; Some listened at the “magical” water-hole frequency, while others preferred alternative promising frequencies; most listened for high-frequency radio signals, but a growing minority is searching for light signals.

All however, share this in common: they are searching for a deliberate signal from an alien civilization, beamed to us across the vastness of space. The only way an alien civilization can be found, is if it is already sending us a beacon, hailing us across the great emptiness. A civilization that chooses to stay quiet, as we ourselves do, would never be found by current SETI projects.

This, however, is about to change. In a presentation today at the American Astronomical Society meeting in Seattle, Washington, Avi Loeb of the Harvard Smithsonian Center for Astrophysics (CfA) proposed a radically new type search for extraterrestrial intelligence. Instead of looking for a beacon, he suggested, we should rather look for normal electromagnetic signals that are produced by a civilization such as our own. In our case these would include radio and television broadcasts, as well as military radar signals that are the strongest of all. According to Loeb it is reasonable to expect that alien civilizations also produce these types of electromagnetic signals, that spill out naturally into space. Most importantly, he argued, we will soon be in a position where we can eavesdrop on them.

The reason why SETI searches to this point have looked for deliberately sent beacons is simple. Whereas a focused transmission can in theory be detected from many light years away with current technology, existing radio telescopes are simply not sensitive enough to distinguish the normal electromagnetic leakage from a technologically advanced alien civilization. Even more problematic is the fact that any radio telescope listening at the common frequencies of radio broadcasts would be swamped by interference from Earth-based transmissions. The only course, therefore, was to listen at high and “quiet” frequencies such as the “water hole,” and hope that aliens are, in fact, trying to contact us.

Click to enlarge > The first tile of the Low Frequency Demonstrator at Miluera This is the first tile of the Low Frequencey Demonstrator of the Miluera Wide-Field Array (LFD-MWA), installed in March, 2005. The tile is one of 500 that will make up the instrument, each with 16 dual-polarization dipole antennas. Thew instrument is located in in Miluera, in the desert of Western Australia. Credit: Harvard Smithsonian CfA

This limitation, argue Loeb and his collaborator, Matias Zaldarriaga of CfA, may soon be a thing of the past. Deep in the western Australian desert, at a site called Miluera, a giant instrument is being built that may be sensitive enough to eavesdrop on alien civilizations. This is the Low Frequency Demonstrator of the Miluera Wide-Field Array (LFD-MWA). When completed, it will contain 8000 dual-polarization dipole antennas, optimized to listen to the universe at frequencies of 80 – 300 MHz. Not only is the LFD-MWA several orders of magnitude more sensitive than previous instruments designed to listen at these frequencies, but its isolated location in a desert in the Southern hemisphere is remarkably free of normal radio interference. Scientists hope that it will remain this way in the long run, and are currently in negotiations with the Australian government to have the region declared a “radio quiet zone.”

In both design and location, the Low Frequency Demonstrator is ideally suited to listen to the day to day transmissions of distant intelligent beings. The frequency range of 80 – 300 MHz, Loeb and Zaldarriaga note, is well within the range of normal radio transmissions on Earth, and is likely to be used by alien civilizations as well. As a result, said Loeb, “soon we may be eavesdropping on signals from Galactic civilizations.”

The Low Frequency Demonstrator is not being built for SETI, but for other research purposes altogether. “The LFD-MWA is a science instrument intended to study the distant young universe” explained Zaldarriaga. Nevertheless, as it has long done at Arecibo, a SETI will piggyback on the regular operations of the instrument and use its data to search for extraterrestrial civilizations. But now, unlike in previous searches, we may be able to detect aliens who are not particularly eager to be found, and may be operating on a technological level similar to our own. “This is the first time in history,” said Loeb, “that humans will be capable of finding a civilization like ours among the stars.”