Carl Sagan Self-Censored an Anatomical Detail on the Pioneer Plaque to Avoid NASA Rejection — and It Is Still Racing Through Deep Space

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The Pioneer 10 and 11 probes carry gold plaques designed by Carl Sagan in three weeks, and the diagram of the naked woman is missing a single anatomical line that earlier sketches included, quietly erased by Sagan himself because he was sure NASA would reject anything more explicit – Image for illustrative purposes only (Image credits: Pixabay)

Carl Sagan made a deliberate decision during the hurried design of the Pioneer 10 plaque to omit one specific line from the drawing of the female figure. He acted on the belief that a more explicit version would never clear NASA review in the short time available. The resulting engraving, completed in roughly three weeks, now travels aboard both Pioneer 10 and Pioneer 11 as they continue their outward journeys far beyond the solar system.

The Tight Timeline That Shaped a Message for the Universe

The plaque concept reached Sagan only months before Pioneer 10’s scheduled launch in March 1972. NASA gave quick approval but allowed just three weeks for the full design. Sagan collaborated with astronomer Frank Drake and artist Linda Salzman Sagan to produce the final layout under that pressure.

Every element had to remain understandable to an intelligence with no shared biology, language, or culture. The design also needed to endure billions of years in the harsh conditions of interstellar space while fitting on a plate no larger than a car license plate. These constraints forced rapid choices about symbols, scale, and posture.

Physics as the Universal Language on the Plaque

The upper-left corner displays the hyperfine transition of neutral hydrogen, a diagram that sets the basic unit of measurement. This transition produces radiation with a 21-centimeter wavelength and a 0.7-nanosecond period. Because hydrogen is the most common element in the universe, any advanced civilization capable of radio astronomy would recognize it.

All other distances and times on the plaque are expressed as multiples of this wavelength or period in binary notation. The female figure, for example, stands eight hydrogen wavelengths tall, corresponding to roughly 168 centimeters. The central starburst pattern maps fourteen pulsars with lines whose lengths and tick marks encode distances and rotation periods from the Sun.

Because pulsars slow at predictable rates, the map functions as both a location marker and a timestamp accurate to within a few thousand years across tens of millions of years. A simpler diagram below shows the solar system with an arrow indicating the probe’s departure from Earth, the third planet outward.

The Human Figures and the Omission That Remained

Linda Salzman Sagan drew the man and woman with neutral ethnic features and fully nude. The man raises his right hand in a gesture meant as a greeting. The figures also convey the presence of opposable thumbs and a specific range of arm movement.

Once the design became public, it drew complaints about nudity on a government spacecraft and questions about the active versus passive poses of the two figures. The final engraving shows the man completely but leaves out the vertical line on the woman’s body that would have indicated the pudendal cleft. Sagan later explained that the choice drew partly from classical Greek sculpture and partly from concern that a more detailed rendering would fail to gain approval within the compressed schedule.

The engraver at Precision Engravers in San Carlos, California, produced the version that flew. Only three original plaques were made: two for the spacecraft and one retained by NASA.

Where the Plaques Are Headed and What They Carry Forward

Pioneer 10’s last signal reached Earth in January 2003 when the probe was about 7.6 billion miles away. Pioneer 11 fell silent earlier, in 1995. Both continue coasting outward, Pioneer 10 toward the star Aldebaran and Pioneer 11 toward the constellation Aquila.

At their current speeds the plaques will take more than two million years to approach those stars. The probability of interception by another intelligence remains extremely low, yet the objects persist as silent records of human presence.

Five years later the Voyager spacecraft carried a far more elaborate message in the form of gold-plated records. Those records reused the hydrogen diagram and pulsar map from the Pioneer plaque, creating a deliberate link between the two efforts.