A rchive Date
[ 27-06-2000 ]
Category
[ Science ]
sub-Categoy
[ Astronomy ]
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[http://www.msnbc.com/news/192803.asp
The big mystery: Looking for aliens
Are we alone? How can we tell? SETI seeks an answer
By Seth Shostak
SPECIAL TO MSNBC
Sept. 24 —Where are the aliens? In a universe of 50 billion galaxies, each comprising a half-trillion stars, it would be remarkably self-centered to believe that our small Earth is the only place where intelligent beings strut and fret. Many folks are convinced that the extraterrestrials are out there. But could we ever prove it?
WHILE FICTIONAL ALIENS get a lot of juicy parts in television and movie dramas, real aliens remain a mystery.
Despite a half-century of intriguing stories about UFOs, abductions and crashed saucers, most scientists are skeptical that creatures from other worlds are touring our planet. To begin with, the energy required to lob a rocket from one star to the next is daunting, irrespective of the technology used. Besides, our arrival on the cosmic stage is still unknown throughout most of the galaxy. Only in the last 50 years have we announced to the cosmos that intelligent beings inhabit Earth.
That announcement consists of radio signals —powerful, high-frequency broadcasts from our television transmitters and military radars. These are the only strong signals to have leaked from Earth, and they are just now reaching the nearest few thousand stars. But the galaxy is far older than Earth. Many advanced civilizations may be spread among its vast stellar neighborhoods. And some of these societies could have begun transmitting radio signals long ago, signals that could be reaching us now.
For this reason, a few dozen scientists have embraced SETI, the search for extraterrestrial intelligence. Their goal is to solve the mystery of whether we're alone. Their game plan is to use large radio telescopes —oversized antennas —coupled to sophisticated digital receivers, in an effort to eavesdrop on cosmic company.
How would they recognize an alien signal? The SETI receivers are designed to hunt for narrow-band broadcasts, transmissions that put a lot of power into a very small slice of the radio spectrum (typically 1 Hz). Such signals would sound like a simple, pure tone if you heard it. Obviously, that's not a terribly interesting transmission, but a narrow-band signal would be the easiest to pick up at great distances. It could be used as a hailing signal to get our attention, and perhaps direct us to more stimulating radio fare. In addition, such narrow-band signals can be made only by transmitters. So SETI researchers needn't be concerned that they will confuse an alien radio beacon with a quasar or pulsar.
All SETI projects listen. None of them broadcasts queries into space. The principal reason for this is that transmitting a cosmic "hello" and then waiting for a reply might take dozens or even hundreds of years. Since we are a relatively young technological society, it makes good sense to listen first. We're the new kids on the galactic block. There may be plenty of radio traffic out there from older civilizations.
Project Phoenix (run by the SETI Institute) is currently conducting the most sensitive SETI search using the massive Arecibo Radio Telescope. Famous from such movies as "GoldenEye" and "Contact," the Arecibo instrument, located in the limestone hills of Puerto Rico, is 1,000 feet across, making it the biggest metal ear anywhere. Project Phoenix is pointing this antenna in the directions of nearby, sunlike stars. Two billion separate frequency channels will be monitored for each star.
No convincing signals from other civilizations have yet been heard, but the SETI scientists are upbeat. After all, the situation could change overnight. A faint radio tone could suddenly and forever solve one of the greatest mysteries of science: our place in the universe of thinking beings.
Seth Shostak is an astronomer working at the SETI Institute. To learn more about the search for extraterrestrials, what they might be like and how humans would react to finding them, you can check out his new book, "Sharing the Universe: Perspectives on Extraterrestrial Life."]
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