Life off Earth - Do Aliens Exist?

The Holy Grail of this new millennium, however, is not to find bugs, but to locate intelligent life. And optimism grows every day. Though we don't expect to find intelligent life on any of the Sun's orbiting worlds, there's a fast-growing list of other places where the aliens might live. Over the past five years, astronomers have been busy finding planets around other stars. The total now stands at 29 with seven found in the last few weeks!

Keck Observatory The Keck Telescope on Hawaii searches the sky for planets around other stars.

Planets beyond

The technique astronomers use to detect "extra-solar" planets relies on the fact that planets "tug" on their parent stars like a dog pulling on a leash. The jerk on the star is very small, but by using sensitive instruments, scientists can measure the degree of wobble and infer the masses and orbits of the encircling planets. The most prolific team of planet-hunters is headed by Geoff Marcy of San Francisco State University. Last year, Marcy's team discovered one star - Upsilon Andromedae that has three planets in tow, making it the first planetary system to be located beyond our own.

So far, the technique is only sensitive enough to pick up planets as massive as Jupiter or greater. But if there are "Jupiters" in existence, there are almost certainly "Earths" sprinkled amongst them it is just that our technology cannot yet winkle them out. In the next few years, by using space-based telescopes, we will undoubtedly be detecting worlds out there like our own.

If intelligent life exists on any of these new worlds, how can we make contact? The distances between the stars are too great for us, at our present stage of development, to go in person. (Our fastest spaceprobes, the Voyagers  which travel 20 times faster than a rifle bullet - would take 40,000 years to reach the nearest stars.).

NAIC, Arecibo Observatory The giant Arecibo Radio Telescope waits for the call from ET...

ET: please phone Earth!

But for at least part of their evolution, aliens will surely communicate over long distances just as we do: by radio waves. They're cheap, fast - travelling at 300,000 km per second - and have no worries about covering vast interstellar distances.

For the last 40 years, a small number of astronomers have been listening-in for the elusive signal from ET using huge radio telescopes like Jodrell Bank, or the vast dish at Arecibo, Puerto Rico. With clever electronic detectors, we can now potentially tune into tens of millions of extraterrestrial radio stations' simultaneously. The name of the game is SETI  the Search for Extraterrestrial Intelligence.