But what if no one's out there at all?

Robin McKie, science editor for The Observer

Sunday May 7, 2006

Despite 40 years of effort, it has yet to produce a single result. Millions of pounds have been spent and thousands of man-hours expended, yet SETI, the Search for Extraterrestrial Intelligence, remains the great unfulfilled hope of modern astronomy. On Friday, at the Royal Astronomical Society, scientists will reassess their prospects of finding aliens in our galaxy. They will gather at a special meeting to explain current programmes and outline a series of projects aimed at finding out whether or not we are alone. 'Twenty years ago, scientists were confident there were at least a million alien civilisations in our galaxy,' said the meeting's organiser, Dr Ian Morison of Jodrell Bank Observatory. 'No one thinks there can be anything like that number now.'

Scientists' failure to hear ET's call accounts for some of this loss of optimism. For 40 years, radio astronomers have trained their telescopes at stars to try to pick up a single 'Hello, I'm here' signal. Earth's own growing ecological woes have also led astronomers to fear that civilisations, if they do emerge, may be extinguishing themselves in very short timespans. 'I am sure life exists on other worlds,' said Morison. 'But it may be rather primitive. Few other worlds may have the right conditions for complex organisms to evolve as they have on Earth.' For example, our moon keeps our planet spinning in a stable manner while our sun does not have wild fluctuations in radiation output. On other worlds, battered by radiation bursts and crashing comets, life may be so disrupted that it has remained rooted at the level of amoebas and primitive pond life. This is known as the 'aliens are scum' scenario.

However, such dwindling hopes have only sharpened astronomers' appetites and at this week's meeting scientists will highlight new methods. One idea - to be outlined by Dr Ian Crawford of Birkbeck College, London - involves using NASA's next manned missions to the moon to search its surface for space debris from alien civilisations. 'We are not talking about digging up monoliths like those in 2001: A Space Odyssey,' he said. 'The idea is to look for microscopic fragments of alien spacecraft.' Russian scientists have calculated that a civilisation capable of space travel would produce massive amounts of debris, like the space junk - old rocket boosters, lens caps dropped by astronauts - that is building up around Earth today. This alien detritus, which would include microscopic particles shorn from spacecraft, could have drifted across space for billion of years, eventually becoming embedded on our moon and ready for astronauts to dig them up. Crawford proposed the idea to NASA at a special meeting on lunar science earlier this month. But this is not the only new concept on offer. Paul Horowitz, of Harvard University, will describe how his team has started surveying the sky for signs of interstellar Morse code. 'We used to think alien civilisations would say "hello" by sending radio signals,' he said. 'However, we have realised they could also do it by beaming out laser pulses, so we have built a telescope that can monitor sections of the sky to pick up these flashes. We have studied 100,000 stars in the last two weeks, but have seen nothing.'

At the same time, Paul Allen - one of the founders of Microsoft - has backed the construction of an array of several hundred radio telescopes in California in a bid to intensify the traditional search for electronic messages from alien civilisations. 'If anyone is beaming signals at us anywhere in our neighbourhood of the galaxy we will pick it up,' added Morison. The trouble with this method is that it will only succeed if aliens are deliberately advertising their existence to the galaxy. Although they may be transmitting radio and TV broadcasts to themselves, these would not be powerful enough to be detected on other worlds. But why would aliens want to announce their presence, some astronomers ask? 'If researchers on Earth wanted to try that sort of thing, they would have to go to their governments and ask for millions of pounds just to send signals into space without knowing if there was anyone out there to pick them up,' added Morison. 'We wouldn't get very far. I am pretty sure of that. So we will just have to hope our alien counterparts have fared a little better with their paymasters.'