SETI - THE SEARCH FOR EXTRATERRESTRIAL LIFE   There may be 10,000 alien races in our Galaxy trying to talk to us You can help join the hunt for ET

SETI at home - How you can help The Lovell Telescope at Jodrell Bank With hundreds of telescopes now involved in the SETI programme, there is lots of data to look through. Spotting strong signals is easy, but finding a weak signal takes lots of computer time. This is where you can help. By downloading the SETI at home screensaver, your computer can help analyse data when it is not being used. You can download the SETI screensaver from the SETI@home website.

There are over four hundred thousand million stars in our Galaxy alone. Where do we start looking for life?

Several tactics are being tried:

• Look for new planets
  
  Over a hundred new worlds have been found already. Find out more.
  
  
• Send messages


The Voyager probes, which are now travelling out of our Solar System, carry messages from Earth in case they are ever found by aliens.


• Listen for signals
  
  Rather than looking for aliens, we can listen for their messages

The easiest thing to do is simply sit back and watch to see if ET tries to contact us. Of course, we might not be able to understand a message if it arrives. But we can at least make a guess as to how ET might try to communicate.

Looking for electromagnetic signals

Our first message from ET will probably be an electromagnetic signal. Electromagnetic signals are waves that can travel through the empty space between the stars. All the light that we see is made from electromagnetic waves, and so are infra-red and ultraviolet light, microwaves, radio waves and X-rays.

Each type of electromagnetic wave has its own frequency. However, we can't watch for all frequencies at once. Can we guess what frequency ET will try?

Talking with microwaves

The best way to send a signal between the stars is by using microwaves. Microwaves are good for two reasons:

• They pass through space well - so there is little chance of them getting absorbed or scattered by clouds of dust between the stars



• Not many other things in the Universe emit microwave radiation - so there is less chance of a message being drowned out by other signals

Even so, the microwave range still contains a lot of frequencies to search over. Can we narrow down the search even further?

Guessing the code for contact

As it happens, two very common compounds - hydrogen gas and hydroxyl molecules (made from a mixture of hydrogen and oxygen) - emit microwaves at frequencies which lie quite close together. When these two compounds are added together they make water, the one substance that's essential for life. Water would be as important to ET as it is to us - so they may well choose to broadcast this signal frequency to make contact.

So, searching the skies for this frequency is a good place to start. Of course, if we don't find anything, we can look at other frequencies later.

Are aliens trying to contact us?

The SETI programme

In 1960, a young astronomer called Frank Drake conducted the first search for signals from extraterrestrials. During the 70s, NASA began a systematic search of the sky. However, they had their funding cut not long after the project had begun.

The privately funded SETI institute was formed in 1984 to continue the search for ET. Their focus now is on targeting over a thousand Sun-like stars, looking for life.

The Drake Equation

In 1961, Frank Drake tried to calculate how many alien civilisations there could be in our galaxy. He wrote an equation - now known as the Drake equation - to estimate how many alien races in our own galaxy might be trying to contact us. His current guess is that there are around 10,000. But this is based on some large assumptions. Only more research will show us how many - if any - alien civilisations exist.