Towards a dialogue with extra-terrestials

Pioneer 10 (1972) and Pioneer 11 (1973) were the first spacecrafts programmed to leave the Solar System.  Astronomers Carl Sagan and Frank Drake have designed two gold-anodized aluminum plaques that were affixed to the spacecrafts.  These plaques feature a pictorial message, in case either Pioneer 10 or 11 would be intercepted by extraterrestrial life.  .

This is a picture of the plaque:

The plaque was intended to open a dialogue with extra-terrestrial life, showing a schematic representation of the hyperfine transition of hydrogen, the relative position of sun within the galaxy, the solar system, and two human figures: a man and a woman.  Notice the raised hand of the man.  It was meant the represent a sign of good will, but of course we don't know what raised extremities might mean to aliens.

It is interesting that there has been controversy about the nudity of the man and woman figures on the plaque. Therefore silhouettes of a man and a woman, rather than the photograph that was initially planned, were included on the golden record that was send with the Voyagers (1977).