In 1972, NASA launched the Pioneer 10 spacecraft with Jupiter as the primary target. After sending back data from this giant world, Pioneer 10 became the first spacecraft to leave our Solar System. NASA received the last, very weak signal from Pioneer 10 in 2003, so as far as we know, Pioneer 10 is still heading towards Aldebaran, located in the constellation Taurus. While unlikely that Pioneer 10 will reach another civilization, NASA (mainly Carl Sagan and Frank Drake) provided Pioneer 10 with a plaque that would hopefully tell another intelligent civilization about our own civilization on Earth.
At the top of the plaque, the two connected circles represent two hydrogen atoms. When hydrogen atoms change energy states, electromagnetic radiation is released, the wavelength of which is about 21 centimeters and the period of which is about 0.7 nanoseconds. Thus the hydrogen atoms provide a standard unit of spatial and temporal measurement. The small tick between the atoms assigns these values of distance and time to the binary 1.
Below the hydrogen atoms is the representation of our cosmic address. At the center of all the lines is the Sun and each radial line signifies the relative distances and directions to known pulsars. Each line has a binary number stating the period of the pulsar. This pulsar map would tell another space-faring civilization both where we are and what time we drew the image. At the very bottom of the plaque is a drawing of our solar system, including just the Sun and the (at the time) 9 planets. Each planet has a binary number telling its distance from the Sun. The arrow and mini pioneer drawing show the path of the spacecraft out of our Solar System.
The final image on the right depicts a man and a woman standing in front of the pioneer spacecraft. The man is holding up an open palm, Earth’s universal greeting. The woman stands with arms down and her weight shifted to show that humans are mobile and flexible. Next to the woman is the binary number 8, with two other ticks indicating this number represents her height. Another civilization could then calculate that the woman is about 5 1/2 feet tall, and use her size to judge the relative sizes of the man and the pioneer spacecraft.
While it is unlikely that any other civilization will find Pioneer 10, it is still fascinating to think that if another civilization did find it, they would be able to discover who we are and where we live in the galaxy. It is also interesting to note that every level of the hierarchy at NASA was all for the idea of giving Pioneer 10 a message for alien races.