Pioneer probes launched in 1970s depict location of the Earth and the human form (pictured above)
Arecibo message, sent to a distant star cluster in 1974, included information about DNA
Giant radio telescopes send messages to a nearby planetary system around red dwarf star Gliese 581
Earth's television broadcasts could also be picked up by aliens
I Love Lucy signals are more than 50 light years away, and our nearest stars have already received Simpsons broadcasts
The earliest we'll hear back from any beamed messages is 2049
