In 1974, a group of scientists sent a radio signal trying to contact intelligent aliens. Here's what they said.
The Arecibo Message was arranged as part of a grand re-opening ceremony at the Arecibo Radio Observatory in 1974. The binary radio signal included information about DNA, the building blocks of life, and where we come from.
It was constructed by Carl Sagan and Frank Drake, who had also created the Pioneer Plaque for the Pioneer 10 and 11 missions, and the Voyager golden record. Both of which were attempts to communicate with an alien species.
The signal was sent to the star cluster M13, which is not expected to be a hotbed for life, but was the best option at the time that the telescope sent the signal. It would take 50,000 years for a species on M13 to reply to the message.
For that reason it's really considered more of a message in a bottle.
METI, or Messaging Extra Terrestrial Intelligence, is a movement that advocates sending messages out to potential aliens, but there are a lot of detractors who think that we may be opening ourselves up to danger from hostile civilizations.