A small number of spacecraft have reached the outer regions of the Solar System and are travelling on outwards. Some of them are carrying messages that might be understood by extra-terrestrial life forms in the exceedingly unlikely event that they find the spacecraft at some time very far into the future. The messages are in the form of the 
Pioneer Plaque and the Voyager Golden Record.
But spacecraft, even at speeds of tens of kilometres per second, are MUCH slower than light, which of course includes radio waves. Also, radio waves spread in all directions. So if anything or anybody finds out about our cosy little planet then it would be far more likely to be by detecting the radio waves that we send out. The outgoing waves are a result of all the TV we watch, the radio we listen to, the communications between place and place, person and person. These radio waves carry organised information.
There have been attempts to send specific messages, such as the
Arecibo Signal. But there are ethical questions wrapped up with the science:
Use the ethics toolkit to discuss the questions below. For each question or group of questions, write down:
- Your conclusion,
- How you made your decision
- Whether and why the decision was difficult
Is it wise to tell extra-terrestrial intelligences, if they exist, that we are here?
If messages are sent, they represent everybody and every animal and everything else on Earth. Should scientists be allowed to speak for us all?
Is any such message an irrelevance? Even if extra-terrestrial intelligences exist, and they take a friendly interest in us, is there any point in communicating with them? They are almost certainly too far away to make a meeting possible.
Have they already been here?
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