A message for extraterrestrials.
Since this craft would be the first man-made object to leave our solar system, the scientists thought it might be possible for a technologically advanced society to detect Pioneer 10 in interstellar space. To otherworldly beings who found this craft, they wanted to communicate the location and appearance of the craft's creators and the time period it was launched.
So, how would Sagan and Drake communicate these messages to an alien race—a race no human had encountered before?
They designed graphics for the Pioneer plaque. How else would you communicate with an alien race that has no knowledge of our language or our appearance or even our planet?
What does this image say to you? Do you think it communicates clearly time, location, and appearance (their primary objectives)?
A lot of thought went into the details of this relatively simple image, which in closer inspection is a lot more complex than it looks:
- At the top is the symbol for hydrogen, chosen because it is the most abundant element in the universe. The small vertical line below the hydrogen symbol represents binary digit 1. The transition of a hydrogen atom from the electron state spin up to electron state spin down can specify a unit of time and a unit of length, which are both used as a legend for measurement in the other images on this plaque. (Math is the universal language, though I believe graphics are a close second.)
- To the right is obviously an image of a man and woman. But look closely at the details. The binary representation of the number 8 is shown between the brackets indicating the woman's height. Using the hydrogen legend, the viewers can calculate her height as 168 cm. Both figures are standing in front front of Pioneer 10 as point of reference to average human size. The man's hand is raised in a gesture of goodwill and to show how our limbs move and show off our handy opposable thumbs.
- Fourteen of the lines radiating from the left image contain long binary numbers that represent periods of pulsars by using the hydrogen atom legend as a unit. The fifteenth line extends from the center behind the figures and depicts the sun's relative distance to the center of the galaxy.
- A schematic diagram of the solar system is seen at the bottom. A small picture of Pioneer 10 is shown following a trajectory past Jupiter and exiting our solar system. Again, binary numbers were added next to each planet to detail their relative distance to the sun.
What would you change if designing it today? Wired UK is holding a contest for a redesign of the Pioneer plaque. Check their site in a few weeks to see what designers 40 years later would do differently.
One criticism of the plaque has to do with the designers making assumptions about their audience. (Of course, how do you know your audience, residing light years away?) Some critics have said they shouldn't have used an arrow to indicate the craft's trajectory.
Arrow graphics are a human, earthly icon, inspired by arrows used in hunter-gatherer societies. Odds are an alien species would not have used or ever seen an arrow.
Guess it really does help to know your audience.