The Arecibo message is an interstellar radio message carrying basic information about humanity and Earth that was sent to the globular star cluster M13 in the hope that extraterrestrial intelligence might receive and decipher it. The message was broadcast into space a single time via frequency modulated radio waves at a ceremony to mark the remodeling of the Arecibo Observatory in Puerto Rico on November 16, 1974.
Background and Development
The Arecibo message was formulated by Frank Drake, then at Cornell University and creator of the Drake equation, with help from Carl Sagan and others. The broadcast was intended not only as a demonstration of human technological achievement but also as a symbolic marker of the Arecibo Observatory's massive equipment upgrade. Prior to 1974, the telescope had undergone a significant remodeling that replaced its original wire mesh reflector with highly reflective aluminum panels, vastly increasing its sensitivity and transmission capabilities. To celebrate this milestone, the scientific community decided to transmit a powerful signal into the cosmos, effectively functioning as a message in a bottle cast into the vast ocean of interstellar space.
Message Structure
The transmission consisted of a simple binary code containing exactly 1,679 bits of data. The number 1,679 was intentionally chosen because it is a semiprime, the product of two prime numbers: 73 and 23. The authors reasoned that any mathematically aware extraterrestrial civilization would recognize this structural property and arrange the data into a two-dimensional grid consisting of 73 rows and 23 columns. When organized in this specific geometric configuration, the binary data yields a visual pictogram. If arranged incorrectly as 23 rows and 73 columns, the resulting image is an unrecognizable, chaotic pattern. The message was transmitted by frequency-shifting a 2,380 MHz radio signal by 10 Hz, with a transmission rate of 10 bits per second. The total broadcast lasted less than three minutes.
Decoding the Contents
When successfully decoded into its 73 by 23 grid, the Arecibo message is divided into seven distinct horizontal sections, traditionally color-coded in later graphical reproductions for analytical clarity. From top to bottom, the message displays: the numbers one through ten in binary format; the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorus, which constitute the building blocks of DNA; the mathematical formulas for the sugars and bases in the nucleotides of DNA; a graphical representation of the DNA double helix structure along with the estimated number of nucleotides in the human genome; a stick figure depicting a human being alongside the average physical height of an adult male and the estimated human population of Earth in 1974; a schematic of the Solar System indicating Earth's position and the relative sizes of the Sun and planets; and finally, a crude representation of the Arecibo Observatory radio telescope itself, along with its physical diameter.
Target Destination
The broadcast was aimed at Messier 13 (M13), a prominent globular cluster located in the constellation of Hercules, approximately 25,000 light-years from Earth. M13 was selected primarily because it was a large, dense collection of stars that was optimally positioned in the sky during the time of the observatory's reopening ceremony. However, because the message will take 25,000 years to reach its destination, and because the cluster is in constant motion, M13 will have shifted from its 1974 coordinates by the time the signal arrives. Consequently, the signal will likely miss the dense core of the cluster, though scientists theorize it may still intersect with peripheral planetary systems. Ultimately, the true purpose of the message was largely symbolic, serving as a profound statement of human existence rather than a genuine attempt to establish immediate two-way interstellar communication.
References
- Staff at the National Astronomy and Ionosphere Center, 'The Arecibo message of November, 1974', Icarus, Vol. 26, Issue 4, 1975, pp. 462-466.
- Carl Sagan, F. D. Drake, Ann Druyan, Timothy Ferris, Jon Lomberg, Linda Salzman Sagan, 'Murmurs of Earth: The Voyager Interstellar Record', Random House, 1978, pp. 52-54.
- A. G. W. Cameron, 'Interstellar Communication: Scientific Perspectives', Houghton Mifflin, 1963, pp. 112-115.
- Philip Morrison, John Billingham, John Wolfe, 'The Search for Extraterrestrial Intelligence (SETI)', NASA SP-419, 1977, pp. 18-22.