Plans to build the world's largest telescope devoted to the search for extra-terrestrial intelligence have been announced.

Scientists want to construct an array of up to 1,000 radio telescopes, some of which may be only 8 ft in size and may be similar to satellite television dishes. The goal will be to seek out signals from civilisations elsewhere in our galaxy.

Electronically connecting many small dishes together means the performance of a much larger one can be attained. The project is estimated to cost less than $25m and could be completed by 2004. It will be among the world's largest radio telescopes.

Building one large radio telescope is very expensive and technically difficult. Even an array of large, custom-built telescopes like the Very Large Array network in New Mexico would cost much more than $25m.

"This represents a shift in the design and construction of radio telescopes," said Jill Tarter, science team leader for the Seti (Search for Extra-Terrestrial Intelligence) Institute. "We hope to demonstrate that a premium instrument need not have a premium price."

University of California at Berkeley researchers are helping to design the array and say that it will be spectacular for radio astronomy too. Because of its unique construction, the telescope could be used simultaneously for Seti and other radio astronomy observations.

Arecibo: the world's largest radio telescope

"The instrument we want to build will have unique capabilities for observing objects from the Solar System to the edge of the Universe," said Professor Leo Blitz, director of the UC Berkeley Radio Astronomy Laboratory. "Our goal is nothing short of standing the way radio astronomy has been done up to now on its head."

The project is called the One Hectare Telescope, or 1hT, because the array will eventually have a collecting area of 10,000 square meters, or one hectare (2.5 acres). By comparison, the world's largest at Arecibo has a collecting area of 73,000 square meters (about 18 acres).

Big project

Seti observations require a large collecting area to find the weak signals expected from an alien transmitter many light years away and also highly sophisticated digital receivers.

Getting time for Seti observations on large radio telescopes is rare and expensive. Seti scientists are able to scan only a few hundred star systems per year. The 1hT would allow this number to increase at least tenfold.

The first goal will be to build a prototype composed of around a dozen small radio dishes at UC Berkeley's Hat Creek Observatory. The Hat Creek Observatory is already the site of a ten-telescope array.

Unlike conventional radio telescopes, the 1hT could be expanded. Adding new dishes to the array could make it larger at relatively low cost.

Listening to the radio

There are strong reasons to believe that any message would be sent as a radio wave, including theories about technology, information transfer, communications theory and the physics of the material in between the stars.

In the 39 years since the first serious search for radio beacons from aliens there have been about 70 searches, so far without success. Hence the drive by Seti scientists for larger and more sensitive telescopes.

Seti is now being taken more seriously by astronomers, as shown by the appointment of the first Professor of Seti studies at the University of California. Professor William Welch has just been appointed to newly created Watson and Marilyn Alberts Chair for Seti at UC Berkeley.