Sending Messages

So if we can't easily go to the stars, and beings from the stars are not likely to be visiting us very often (supermarket tabloids notwithstanding!), can we at least imagine communicating with them?

Messages on Spacecraft

Several messages have been attached to spacecraft launched from Earth. The Voyager I and II spacecraft launched in 1977 are traveling out of the Solar System. The adjacent image shows a plaque that is attached to each, intended as a greeting to any extraterrestrial civilation that might find them. Given the emptiness of interstellar space, it is admittedly very unlikely that the Voyagers would be found by an extraterrestrial civilization (but see the right panel!). However, the content of the plaque is a useful exercise in the issue of how we would deal with an encounter with intelligent living things from beyond our own planet. The content of the plaque is discussed here.

Sending Radio Messages

By far our best hope for communicating with extraterrestrial civilizations is by radio transmissions. Indeed, since the invention of radio and television, signals from our planet have been leaking into space that a sufficiently advanced civilization within 50 light years could have intercepted by now (one shudders to think of their opinion of Gilligan's Island!). There have also been deliberate attempts to send messages. The following image was sent toward the globular cluster M13 in Hercules by the Arecibo Radio Observatory at its dedication in 1974.

It was encoded as a binary signal (a string of zeros and ones) and contains in pictorial form and binary code some examples of human knowledge and information about our species and planet. From left to right: the numbers from 1-10, atomic numbers for some elements, formulas for nucleotide components in DNA, the DNA double helix, and information about human beings, the Solar System, and the Arecibo radio telescope.