The Allen Telescope Array and Seti

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We could be forgiven mistaking the Allen Telescope Array for the "Alien Telescope Array" at first glance. Much of the work it does and will do is related to the search for extraterrestrial intelligence (SETI) after all. But the Allen Telescope Array or ATA is primarily funded by the Paul G. Allen Foundation; Allen is the co-founder of Microsoft.

The idea for ATA arose from workshops held by the SETI Institute in 1997, these produced a paper entitled "SETI 2020" that envisaged a one hectare telescope (1HT), approximately 100 meters squared, based on a large number of small dishes (LSND) array. The SETI Institute obtained funding from Paul Allen in 2001 and in collaboration with the Radio Astronomy Lab of the University of California Berkeley started work on design. It is intended for the array to total 350 radio telescope dishes, but an initial project called ATA-42 for an array of 42 dishes began construction at the Hat Creek Radio Observatory in northern California in 2004 and reached the testing stage in October of 2007.

Scientists and engineers utilize the flexibility of the array design to conduct surveys of the astrophysical sky and search for an extraterrestrial, technological civilization at the same time. This is done by using three independent, intermediate frequency (IF) systems surveying the narrowband frequency range from 1410 to 1730 MHz (megahertz). A twenty degree (2 x 10) block of the sky, the field of view, is surveyed over a period of several months.

A position in the field of view is tracked for up to five hours using three phased beams that monitor each 20 MHz segment of the IF range for 98 seconds. By comparing the observations from the three beams, signals originating from terrestrial sources or artificial satellites orbiting the Earth can be eliminated from the results.

Besides the SETI objective of detecting artificially generated radio signals indicating a technologically advanced extraterrestrial civilization, this allows radio astronomy examination of our Milky Way galaxy and others, and the study of gamma ray bursts and transient radio sources. This increases our knowledge of our Universe, whether we get a SETI success or not. Even when the array is at its 350 disk full strength, detecting an extraterrestrial civilization will be very difficult.

The one radio message we have broadcast to anyone listening, from Arecibo in 1974, was only three minutes long. In the science fiction novel "Contact" by Carl Sagan we received a message from outer space that was, if I recall correctly, about 26 minutes long. But that fictional message repeated, there was a pause when it ended and then it started again. Our three minute message did not repeat. Even if an alien civilization sent a message in our direction, if they did the same as us, we would need to be looking at exactly the right spot in the sky at the right time to receive it. Don't hold your breathe for a positive result from SETI, it could take thousands of years of repeat surveys.

Much of our own communications now go from Earth to one of our artificial satellites on tight-beam to be broadcast down to us. So less of our communications traffic is traveling out from our planet now than when most of our communications were broadcast from terrestrial communications towers. Detecting such communications from even nearby stars may be unlikely, we don't really know. We are a long way from getting to a nearby star system with even a robot probe that could look back our way and tell us if it can detect us!

More about this author: Perry McCarney

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