THE discovery of a planet like Earth orbiting another sun would be an extraordinary event. But it could happen in our lifetime if we can make telescopes that are precise and sensitive enough.
Bigger telescopes, however, cost a fortune. An 8-metre optical telescope costs in the region of $100 million and the price rises steeply with every small increase in diameter. There is little more to be gained by improving detectors 鈥� modern CCDs are already more than 90 per cent efficient. What we need is either a way to make bigger telescopes cheaper, or a better site from which to observe.
The good news is that one of the least habitable environments on Earth 鈥� the Antarctic Plateau 鈥� may turn out to be the best place from which to search for new habitable planets. To begin with, it is cold with temperatures dropping to 鈭�85 掳C in winter. This dramatically reduces thermal radiation both from the atmosphere and the telescope itself, which would otherwise mask weak astronomical signals. Measurements at the South Pole have shown that intense cold reduces this background by up to two orders of magnitude. This immediately implies that sensitivity will increase by a factor of 10. Or, put another way, an 8-metre infrared telescope on the Antarctic Plateau could achieve the sensitivity of a hypothetical 25-metre telescope anywhere else on Earth.
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However, the best news arrived from Australia earlier this year when Jon Lawrence and his colleagues at the University of New South Wales set up a robotic observatory at Dome C, the site of the new French-Italian Concordia Station in Antarctica. They discovered that the 鈥渟eeing鈥�, or sharpness of the astronomical images, was 2 to 3 times better than at the very best sites currently used by astronomers, such as those in Chile, Hawaii and the Canary Islands. In an article published in this week鈥檚 Nature, they present these findings and explore the implications for telescope designers. Their results confirm predictions made more than a decade ago by Peter Gillingham of the Anglo-Australian Observatory in New South Wales, who recognised that the unique weather patterns over the Antarctic Plateau eliminate most of the temperature variations and turbulence that degrade astronomical images.
But what about the blizzards? How can any telescope be expected to survive the 300-kilometres-per-hour winds and massive storms that can dump metres of snow in a few hours? Here we have to confront our prejudices, conditioned since early childhood by stories of frostbitten heroes battling impossible odds. The truth is that Antarctica is a big place, roughly twice the size of the US. We should not be too surprised to find that the climate in one part of the continent is very different to the climate in others.
At an altitude of 3250 metres, Dome C is high, dry and extremely cold. There is so little wind it is eerie. Peak wind speeds are extremely low and the median speed is 2.7 metres per second, roughly half the speed experienced at major observatories such as Paranal in Chile. The plateau is the driest desert on Earth. The only precipitation is the occasional fall of tiny ice crystals, which, in an average year, bring the equivalent of just 35 millimetres of water.
OK, so conditions may be favourable to operating a big telescope, but what about the cost of getting it there? Wouldn鈥檛 it be cheaper and easier to launch our telescope into space? Once more reality is obscured by our image of bearded heroes dragging agonisingly heavy sleds across an icy wasteland of crevasse fields.
Decades of development, especially by French and Australian teams, have made the so-called 鈥渢ractor traverse鈥� from coast to plateau routine. The cost is about $3 per kilogram. Compared with a rocket launch to low Earth orbit at $10,000 to $15,000 per kilogram, it is fair to say that Antarctica is 鈥渁lmost like space, but with a free launch鈥�. And if you鈥檙e in a hurry, you can always fly. Since 1957 US scientists have flown from Christchurch in New Zealand to McMurdo 鈥� a 5-hour trip. Three hours later you can be at the South Pole.
There are some drawbacks. While the total amount of 鈥渘ight鈥� is exactly the same as anywhere else on Earth, astronomical 鈥渄ark time鈥�, when the sun is more than 18 degrees below the horizon, is much less. And aurorae are at best a nuisance, albeit a spectacular one. The further south you go, the less of the sky you see, until you reach the South Pole where you see the same piece of sky all the time. Of course, this has advantages and disadvantages.
So what are we waiting for? Radio astronomers have already achieved remarkable success in Antarctica with experiments such as DASI, which last year discovered polarisation in the cosmic microwave background. Telescopes at Amundsen-Scott Station have operated successfully for many years, but their mediocre seeing has deterred optical astronomers. Now we know Dome C is not only the driest, coldest, clearest site on Earth, but also has the best seeing and the lowest wind. As the explorer Robert Falcon Scott might have said (but didn鈥檛): 鈥淕reat God! This is a wonderful place鈥︹��