BioEd Online

Two remote tracts of countryside on two different continents were today put forward as contenders to host an enormous radio telescope. When completed, the Square Kilometre Array will consist of thousands of small dishes and antennas, arranged in clusters over an area some 3,000 kilometres across.

The sites in Australia and South Africa were selected from four bids submitted to the international committee coordinating the project. The other two sites an area in the karst mountains of southeastern China and a high plain near the Andes in Argentina were knocked out of the running.

The Square Kilometre Array (SKA) is being championed by astronomers interested in studying the universe using low-frequency radio waves. The SKA's many small dishes will give it a total collecting area of roughly the square kilometre of its name, making it possible for the instrument to see much fainter and more distant objects than ever before.

Six key science projects have been proposed for the telescope, including a study of the mysterious 'dark energy' driving the expansion of the Universe, probes of the era in which the first stars switched on and imaging of planet-forming regions. Astronomers also hope that the telescope's unprecedented sensitivity will turn up entirely new phenomena.

Two down

The selection process involved month-long treks into the wilds of the four would-be host countries to measure the amount of radio 'noise' in the region of each proposed site. "The general idea is that you want to have the instruments set up in a region that's as far away from human activity as possible," says Rob Millenaar of the Astron observatory in the Netherlands, who led the expeditions.

The journeys involved long train and truck journeys, after which Millenaar and his team were often stationed in remote farmhouses. And the testing had some hiccups. The dry atmosphere and windy conditions in Argentina led to the build-up of static electricity in the equipment, which caused some parts to fail. Lightning strikes in China and a two-week delay at customs also presented challenges. It was certainly worth the trip, though, says Millenaar. "Being in all these strange places for a long time, working with the local people, is a real privilege."

The monitoring revealed all four bid regions to be quiet enough for the SKA. But in China, the dramatic, vegetation-clad hills proved problematic. "It was impossible to fit the design into the landscape," says Phil Diamond, a member of the 21-strong steering committee.

Argentina was eliminated because of turbulence in the ionosphere over the site. The shape of the Earth's magnetic field directs charged particles into the atmosphere near the area, causing oscillations that muddle the propagation of low frequency radio waves.

Two to go

This leaves the bids of Australia and South Africa on the shortlist. Both sites, being in the Southern Hemisphere, should have a good view of objects around the galaxy's central black hole.

South Africa aims to place the centre of the SKA in the flat expanse of the Karoo desert, with other clusters of dishes set up in neighbouring countries and on the island of Madagascar. Australia's core site is in western outback country, home to farmers, cattle and sheep. Further dishes might be installed in New Zealand to bring the SKA up to its full size.

The decision was made at the end of August, but released to the public today. Though a lot of jobs and national astronomical pride rested on the decision, Diamond says everyone accepted the outcome gracefully. "Everyone involved, even those people from the sites that were unsuccessful, regarded it as a very fair and equitable process," he says.

While the shortlist was based on scientific merit, the final decision on the telescope's home is likely to be determined by money and politics. The telescope's overall design is set to be finalised in 2009; they aim to have funding arranged for construction to begin in 2013, allowing operations to start in 2015. The SKA is forecast to cost around US$1 billion.

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