Antarctic expeditions could soon be on astronomers' itineraries. Credit: © Tony Travouillon

The calm air above part of the Antarctic makes it the best place on Earth for astronomy, according to the scientists who propose building a telescope in the icy wilderness.

The researchers studied atmospheric turbulence above the Dome C research station, located 1,670 kilometres away from the South Pole. They found the air was so still that the light from distant stars was disrupted far less than anywhere else on the planet.

"Dome C is the best ground-based site to develop a new astronomical observatory," says Michael Ashley, an astrophysicist from the University of New South Wales in Sydney, Australia, and colleagues in a paper published in this week's Nature1.

Twinkle, twinkle little star

Astronomers using ground-based telescopes are usually plagued by the Earth's atmosphere, which bends starlight back and forth as the beams pass through pockets of air with different densities. The effect is similar to the apparent shimmering of a desert, caused by looking through hot air rising from the scorched sand.

Dome C is the best ground-based site to develop a new astronomical observatory. Michael Ashley , University of New South Wales, Australia

So when the starlight reaches us, we see the twinkling effect immortalized in the nursery rhyme. This may be loved by children, but it is loathed by astronomers as it reduces the quality of their observations.

Ashley and his colleagues decided to test the potential of Antarctica's Dome C research station. The station is populated in the summer months by scientists studying the hole in the ozone layer or extracting ice cores in order to work out how the Earth's climate has changed over hundreds of thousands of years.

The team set up an automated laboratory there in January 2004 to monitor the atmosphere between March and May, during part of Antarctica's six-month winter 'night'. Even at high-altitude sites elsewhere on Earth, stars seem to jitter in the sky, moving by about 140 millionths of a degree. But the researchers found that over Dome C, the jitter was as low as 19 millionths of a degree, by far the best value ever reported.

The researchers estimate that in order to compare to an optical or infrared telescope built at Dome C, a telescope built at one of the next best sites around the world would have to be two or three times as large. A Dome C telescope could even work on projects that would otherwise require a space mission, they add, and could potentially assist in the hunt for Earth-like planets beyond our solar system.

Remote location

Antarctica was already known to be an attractive location for a telescope because it is so far away from the interference of urban light, heat and smog, and it is also one of the least cloudy places on Earth. Ashley and other colleagues at the University of New South Wales had previously proposed building a telescope at Dome C, but the plan failed to secure funding in 2001.

Ashley hopes the team's concrete evidence of Dome C's high visibility conditions will boost its new proposal, called PILOT. With a two-metre mirror, it would cost between US$5 million and US$7 million to build, and could be completed by 2008, he says.

Telescopes have been built at increasingly high altitude to reduce the distance the starlight must travel through our turbulent atmosphere. Some telescopes are fitted with hundreds of tiny motors, which move the telescope's mirror to compensate for the jittering. But 'adaptive optics' can only reduce, and not eliminate the effect.

The Hubble Space Telescope avoids the jittering problem altogether, because it orbits above our atmosphere. "But it's certainly easier to build in Antarctica than it is in space," says Martin Rees, an astronomer at the University of Cambridge and England?s astronomer royal.

Environmental control

Some might fear that building a telescope at in the Antarctic would disrupt the pristine environment there. "In Antarctica we have the most stringent environmental protocols in the world," says John Shears, environmental officer for the British Antarctic Survey, based in Cambridge. "Any proposal would require a rigorous impact assessment." But the telescope's ability to deliver world-class science would weigh heavily in its favour, he adds.

Ashley and his colleagues point out that the established infrastructure at Dome C would make it much easier to build a telescope there, and limit the impact of the project on its surroundings.

"I'm an environmentally friendly person, and I'd say 'Go for it'," says Colin Summerhayes of the Scott Polar Research Institute in Cambridge. "You're making the least environmental impact by building at Dome C."

There is no wildlife in that part of the Antarctica to disturb, whereas a telescope built in a remote part of Chile, for example, would have a much greater effect on the environment, adds Shears.