Messages...but not from SETI

For around half a century humans have been announcing their presence to the cosmos. Radio, television and radar signals all leak away from the planet and into space. It's an awful thought, but instead of some carefully worded message constructed by United Nationals on behalf of all humanity, if any extraterrestrial intelligence pick up those signals they would be judging our cultural level by episodes of 'I Love Lucy' and the ilk.

All SETI projects are 'passive', which means researchers only listen for evidence of other intelligences much like listening to a radio program - the radio station doesn't know who is tuned in, and neither would ET know SETI is listening.

In that case, why doesn't SETI send messages? There are two reasons. One is that humans are technologically very young - just about half a century in radio astronomy terms - and a message would have to be repeatedly sent with a dedicated beacon to raise the chances of being heard. Second is that the stars (other suns) are very far apart. An interstellar call to even the closest star system to the sun, travlling at the speed of light - 300,000 kilometres per second - would take 4.3 years to get there and 4.3 years to the reply to be heard..."excuse me, can you say that again?"...not a snappy telephone conversation (and not in perfect English or even with any concept of what was said in the first place). The reality is that if intelligence exists elsewhere in the galaxy, the nearest neighbours may be hundreds of light years away, taking many human lifetimes just to get a reply - if one was forthcoming.

Only one message has been sent from Earth using a radio telescope non-commercially and that was sent by Dr Frank Drake in 1974 (shown right). The purpose was primarily to celebrate the upgrade of the Arecibo radio telescope in Puerto Rico. The message was sent only once and towards the Hercules globular star cluster some 25,000 light years away. If anyone is out there, and is listening at exactly the right time on exactly the right frequency and decides to reply we will know - if we are listening at the right time on exactly the right frequency some 50,000 years from now. The odds are very long - but arguably not impossible!

In spite of the harsh reality on the chances of being heard with a single sending of the 1974 message, it still served the main purpose - Arecibo had just gone through three years of upgrade to allow the 1,000 foot dish to peer further into the universe.

Drake, now President of the SETI Institute in California, largely devised the message. The message was turned into two pitched tones so the 250 dignitaries gathered on a hot tropical afternoon to witness the ceremony could hear the message as it was being sent. For 169 seconds the message sang a song of Earth to the stars with a power that outshone the sun on a single frequency. "That out to get someone's attention, I thought," said Drake later in his book "Is Anyone Out There?"

Drake wrote that the sound of the message was "like the trilling of a strange musical theme played on a giant electronic synthesiser. The song, unique and full of yearning, affected us strongly.

"...I saw women in sleeveless dresses rub chills from their arms. I saw the eyes of sober scientists filled with tears. And mine did too."

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Drake's 1974 message

It gives (from the top and left to right) the numbers one to ten, a description of hydrogen and carbon, the number of codons in DNA and DNA itself, a human with Earth's population on the left (3.8 billion in 1974 compared to 6 billion in 2000) and on the right the average height of a human, the Arecibo radio telescope and a description of the solar system

(Picture by Frank Drake, Arecibo)