We are making dangerous discoveries in space. In April, astronomers found, on our cosmic doorstep, a planet dubbed Gliese 581c. Nestling close to a dim red star, it's a rocky world only a little larger than Earth. Like Earth, it could support liquid water. And to scientists, liquid water means the possibility of life.

Gliese 581c must be an ancient world, for it circles a star that is far older than our sun. The question is, has any advanced life evolved on that planet, or on the many other places that must be suitable sites, not so very far away?

Recently, astronomers told the British Government that we might find life in space. It is only a matter of time, this year perhaps, before astronomers detect a planet even more similar in size and mass to our Earth, circling another star. And when we find that planet, we may discover a lot more than new oceans and land masses.

Astronomers have been looking for intelligent life in space since 1960, when Frank Drake started Project Ozma, using a radio telescope to listen for signals from two nearby sun-like stars - Drake knew that radio waves travel more easily through the cosmos than light waves. He didn't hear anything back. Since then, our searches have become more thorough thanks to larger radio telescopes and more sophisticated computers that look for fainter signals. But we still have no signal from ET. Should we want to?

This is not just a matter for astronomical research involving distant worlds and academic questions. Could it be that, from across the gulf of space, as H. G. Wells put it, there may emerge an alien threat? That only happens in lurid science fiction films, doesn't it? Well, the threat is real enough to worry many scientists, who make a simple but increasingly urgent point: if we don't know what's out there, why on earth are we deliberately beaming messages into space, to try to contact these civilisations about whom we know precisely nothing?

The searchers are undeterred. They argue that because of the vastness of space - even if there are 10,000 transmitting societies nestled in the stellar arms of the Milky Way - we might have to search millions of star systems to find just one.

The SETI (Search for Extra-Terrestrial Intelligence) Institute in California is the only such group that searches the cosmos for signs of intelligent alien life. It does so by listening for radio signals. SETI, which was founded in 1984, has 100 scientists, educators and support staff. Its funding from the American government was cut off in 1992 and it now relies on private donations.

The institute's Project Phoenix was the most ambitious search for extraterrestrial intelligence ever undertaken. From February 1995 to March 2004, Phoenix conducted three observing campaigns on some of the world's largest radio telescopes, targeting stars within 240 light years of Earth. In more than 11,000 hours of observing, using telescopes in Australia, West Virginia and Puerto Rico, the project "tuned in" to more than 800 stars. No ET signals were detected.

The next stage in the search is the Allen Telescope Array, currently under construction in California. Partly funded by Microsoft billionaire Paul Allen, it will eventually consist of 350 six-metre dishes making synchronised sweeps of the sky looking for alien signals. But rather than just listening, some want to announce our presence to the cosmos. In 1974, the then newly resurfaced Arecibo radio telescope in Puerto Rico (made famous in the James Bond film Goldeneye) reversed its usual role of just listening, and transmitted a series of radio pulses towards the M13 star cluster. It sent 1679 pulses in all, which, when arranged in binary form into 23 columns and 73 rows, would form a message from humanity. It was seen as a symbolic gesture, showing those on Earth that we had the technology to send a signal across our galaxy and - if we were on the other side of the relationship - to receive a signal as well. But some scientists objected. Sir Martin Ryle, Britain's astronomer royal at the time, warned that "any creatures out there (might be) malevolent or hungry".

Full article: http://www.theage.com.au/news/general/is-anybody-out-there/2007/08/03/1185648134898.html