The Pioneer Plaques, attached to the Pioneer 10 and Pioneer 11 spacecraft launched in 1972 and 1973 respectively, serve as humanity’s inaugural interstellar messages. Created by a team led by famed astronomer Carl Sagan, the plaques are intended to communicate to extraterrestrial life about the origin of the spacecraft.
Designing Universal Communication
The primary challenge for Sagan and his team was to design a message that could be understood by beings without any prior knowledge of Earth or humans. This called for a universal language – one grounded in science, mathematics, and easily recognizable symbols.
The plaques are gold-anodized aluminum measuring 9 by 6 inches, etched with multiple diagrams. The material was chosen for its resistance to erosion and corrosion, ensuring the messages could endure the rigors of space travel.
Figures of Humanity
The most striking feature on the plaques are the naked figures of a man and woman, representing humanity. The figures are drawn in a way that shows the body proportions, while the man’s right hand is raised in a gesture of goodwill. This was intended to signify peaceful intentions.
Hyperfine Transition of Hydrogen
The plaques depict the hyperfine transition of hydrogen, the most abundant element in the universe. This is a universal scientific phenomenon involving the spin-flip transition of the electron in a hydrogen atom. Its significance is twofold. Firstly, it is a ubiquitous event in the cosmos and hence recognizable by scientifically advanced extraterrestrial life. Secondly, it provides a universal unit of measurement for time (frequency) and length, based on the period and wavelength of radiation it emits.
Solar System and Trajectory
Also etched on the plaques is a representation of our solar system with a small depiction of the Pioneer spacecraft showing its origin and trajectory. This diagram was included to communicate the spacecraft’s place of origin in the event of discovery by extraterrestrial beings.
Critiques and Legacy
The Pioneer plaques have been subjects of both admiration and critique. Critics have pointed out that the plaques’ messages are based on many assumptions about extraterrestrial life — that they would have vision, understand the images, and have knowledge of hydrogen’s hyperfine transition.
The plaques also sparked controversy due to the nudity of the human figures, which some considered inappropriate. However, the decision was defended on the grounds of biological accuracy.
Despite these criticisms, the Pioneer plaques symbolize a hopeful and significant moment in human history. They represent humanity’s curiosity, ambition, and the aspiration to reach beyond our own world and make contact with the cosmos.
Pioneer 10 is heading towards the star Aldebaran in the Taurus constellation and will take more than 2 million ears to reach it. Pioneer 11 is headed toward the constellation of Aquila (The Eagle), Northwest of the constellation of Sagittarius. Pioneer 11 will pass near one of the stars in the constellation in about 4 million years.