A RADICAL design of telescope is about to transform the search for extraterrestrial intelligence (SETI) into a full-time effort a hundred times more powerful than before. SETIastronomers are planning to link 350 small, off-the-shelf dishes into one huge telescope that will scan the skies 24 hours a day.
So far, the largest number of dishes to be used together is 27, in the Very Large Array (VLA) telescope near Socorro, New Mexico. But the VLA cost hundreds of millions of dollars to build. SETI receives no government funding, so to achieve comparable results at a fraction of the cost it is setting up a huge collection of cheap, 6-metre dishes, as used for satellite TV receivers across the world.
So far, three of the dishes have been installed at Hat Creek, California, and they are being put through their paces in critical tests that will show how the final array will work. The tests, expected to be completed by the end of March, will show whether the three can function together effectively as one instrument. 鈥淥nce you have done three, that鈥檚 the hard thing,鈥� says SETI senior astronomer Seth Shostak. 鈥淎fter that, it鈥檚 just scaling up.鈥�
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When completed in 2005, the Allen Telescope Array (ATA) will have a total collecting area of about 10,000 square metres, half that of the VLA but far more than has ever been available to devote to searching for alien signals. And it will have cost just $40 million.
Astronomers will be able to steer the array to any point in the sky, and it will cover a wider frequency range than any previous SETI telescope 鈥� from 0.5 to 11 gigahertz. Because it is an array, it will be able to image segments of sky 2.5 degrees wide at a time, instead of a single point.
鈥淓ven from day one, the search will be 100 times quicker than what we鈥檙e doing now,鈥� says Shostak. He hopes that will enable SETI to expand beyond present searches that try to cover a few thousand stars, to searching 鈥渉undreds of thousands, maybe millions of star systems鈥�. To an ET enthusiast, that鈥檚 an exciting prospect. 鈥淭his is the first instrument I think has real chance of detecting a signal within our lifetimes,鈥� Shostak says. 鈥淭his instrument changes the rules of the game.鈥�
If the innovative design works, the telescope could also change how other radio astronomers scan the sky, by providing a key proof of concept for one of the proposed designs for the Square Kilometre Array. This monster will have 100 times the collecting area of the ATA, and 10 times that of the world鈥檚 largest existing telescope, a 305-metre-wide dish at Arecibo, Puerto Rico.
Many different ideas have been proposed for the design of the One Kilometre Array. The ATA would provide a valuable demonstration that could tip the balance in favour of the cheap and cheerful approach.