The aliens are out there SOMEWHERE IN space, aliens are broadcasting a radio signal, hoping to make contact with other intelligent life forms. Somewhere on Earth, a group of people are scanning the skies with antennae hoping to hear something from extra-terrestrials (ETs). Meet Dr Seth Shostak, an astronomer at the United States-based Search for Extra-Terrestrial Intelligence (SETI) Institute, whose job is to listen to what ETs have to say, and to find out where they are calling from. The energetic, self-proclaimed 'very old man' was in Hong Kong recently to see the Leonid meteor shower. Twice a year he goes to Puerto Rico on a three-week search for ETs. He uses the world's largest radio telescope, the Arecibo, which was featured in the movie Contact. The telescope's satellite dish is built into a valley and is the size of 373 tennis courts. Each night, Dr Shostak points the telescope at a star similar to the sun and looks for possible signals sent by aliens from planets orbiting the star. A lot of radio signals come through. He monitors about two billion channels - 28 million at a time - for every star system. It takes about a day to observe a star so Dr Shostak observes about 50 on his two trips to Puerto Rico each year. 'It is always fun. It is like going to a monastery: You live there, you eat there, you don't go anywhere,' he says. 'The problem is, ETs never send us an e-mail saying where on the radio dial the signal might be. So we have to cover a lot of the dial to have some chance of hearing [them]. This is not an efficient way of doing it, but it is all we can do right now.' Long before joining SETI, Dr Shostak studied galaxies, but when the institute called, he could not resist. 'When I was in graduate school, I remember reading a book about looking for ET intelligence at three in the morning. I was sitting all alone in an observatory in the California desert with a radio telescope outside the window pointed at a galaxy.' When he realised the telescope could be used for communication from one star system to another, he knew he had to pursue the search for life in outer space. 'I thought that was a romantic idea. Later on . . . when I was invited [to join] SETI, I said 'yes'.' However, ETs are unlikely to look like us, Dr Shostak says. 'All the animals that share this planet with us went through a common evolution process, but they don't look like us. If our fellow creatures are not like us, aliens probably don't look like us either,' he explains. ETs may exist in the form of bacteria or plants, but those Dr Shostak is interested in are intelligent enough to make radio transmitters. That means they cannot be too big or too small, he says. If they are too small, they will have few brain cells and will be unable to think very well. If they are too big, they may be too clumsy to build advanced machines. 'They probably need eyes, some appendages, perhaps four or six, but probably not 100, because they will then be spending all this time worrying about them. 'But it is possible that the kind of intelligence we meet may not be biological,' he cautions. 'Think about Earth a million years from now. Maybe the only thing left is computers. They can think much better than us. Using artificial intelligence, they can evolve very quickly. 'So the signals we hear may be from machines, not the soft squishy aliens we see in movies.' The first SETI experiment was conducted in 1960, but so far, 'we have found nothing,' says Dr Shostak. 'My mother sometimes says that maybe I should get a real job. 'But chances are getting better because the technology is improving. The new telescope that we are building will enable us to observe 50,000 stars a year. I honestly think that there is a pretty good chance of finding a signal in 20 years' time.'