As the first two spacecraft designed to leave our planetary solar system (in 1983 and 1990, respectively) Pioneer 10 & 11 carry a graphic message engraved on a 6 x 9 inch gold anodized plaque bolted to the spacecraft's body.

On the plaque a man and woman stand in front of an outline of the spacecraft. The man's hand is raised in a gesture of good will. The images of the man and woman were based on an average of adult humans' body measurements.

The key to translating the plaque lies in understanding the breakdown of the most common element in the universe - hydrogen. This element is illustrated in the left-hand corner of the plaque in schematic form showing the hyperfine transition of neutral atomic hydrogen. Anyone from a scientifically educated civilization having enough knowledge of hydrogen would be able to translate the message.