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In November 1974, humanity reached out to the cosmos with its first deliberate interstellar message. The encoded transmission, crafted with care, curiosity, and a touch of boldness, has yet to reach its intended destination. Yet, this groundbreaking act is a true symbol of our yearning to connect with intelligent alien life. Decades later, the Arecibo Message remains a cornerstone of humanity’s search for life in the cosmos.
Where did scientists send this message? What exactly did they put inside it? And can we expect to receive a response? Click through this gallery to find out.
The Arecibo Message was sent into the cosmos on November 16, 1974, from the Arecibo Observatory in Puerto Rico. It was nothing more than a brief stream of binary data, delivered as a long-distance “hello” to unknown cosmic neighbors.
At the time that the message was sent, the Arecibo Observatory was the most sensitive tool for exploring the universe. It took three years to construct, opening its doors in 1963.
The gigantic bowl-shaped radio dish of the observatory was built in a natural sinkhole. The steel platform suspended above it weighed an astonishing 900 US tons (816 metric tons).
The Arecibo Message marked the inauguration of the telescope’s powerful new transmission capabilities, which allowed it to broadcast signals with unprecedented reach and strength. In fact, it was able to transmit signals with a power twenty times greater than the combined output of all the power plants on Earth at that time.
Astronomer Frank Drake (renowned for the Drake Equation, which is used to estimate the number of extraterrestrial civilizations in the Milky Way Galaxy) designed the message that would be sent. His innovative approach framed humanity’s attempt to communicate with aliens in the simplest term: the binary code.
Binary code, which consists of nothing more than ones and zeros, was used in the Arecibo Message because it is a simple and universal system that can be understood by any being capable of basic mathematical reasoning.
Graduate students at Cornell University helped refine Drake’s design, contributing key elements to the message that would inevitably be sent.
The final message contained 1,679 bits (short for “binary digits”) arranged in a grid of 73 rows by 23 columns. The message consists of seven parts that encode various pieces of information about humanity.
The first section of the Arecibo Message lists the numbers from one to 10 in binary. This serves as a foundation for the message, demonstrating to aliens the concept of counting and binary representation, which should be intelligible to other advanced beings.
This section uses the numbers one, six, seven, eight, and 15, which are the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorus. These elements are fundamental to life on Earth and form the building blocks of DNA.
The third part outlines the chemical formulas of 12 organic molecules (or “nucleotides”) that make up DNA. All of Earth's life forms are constructed using the same genetic framework, and this section shows what that framework looks like using atomic numbers of elements.
This section graphically represents the iconic double-helix structure of DNA, with lines connecting its components. It also includes the number 4,294,967,296 in binary, which represents the approximate number of base pairs in human DNA.
A human figure stands at the center of this section, accompanied by a vertical line on the left to indicate the average height of humans (about 5'9", or 175 cm, encoded using the wavelength of the transmission). On the right, the Earth's human population (approximately 4.3 billion in 1974) is encoded in binary.
The sixth part of the message is a graphical representation of the solar system. The Sun and the nine planets (including Pluto at the time) are depicted, with Earth shifted up to show the origin of the message.
The final section displays the Arecibo radio telescope as the transmission source. Its shape is depicted in binary alongside its approximate diameter of 1,004 ft (306 meters). The letter “M” was put there to show that the curved line is a concave mirror.
The message, which was broadcast for three minutes at a frequency of 2380 megahertz, wasn’t about expecting a reply. Not only was it humanity’s way of saying, “We’re here,” but it also demonstrated our potential for interstellar communication.
The encoded transmission was sent in the direction of Messier 13, a massive star cluster in the Hercules constellation some 25,000 light-years away.
Given Messier 13’s distance from Earth, any reply could take about 50,000 years. The experiment was less about conversation and more about imagining the possibilities of contact across space and time.
Critics have warned that broadcasting Earth’s location could invite danger. Criticisms such as these have been known to draw on speculative theories like the Dark Forest, where civilizations hide to avoid attracting hostile forces.
Today, international protocols like those from the SETI Institute urge broader discussions before sending interstellar messages, placing emphasis on inclusivity and ethical responsibility in crafting future communications.
While the Arecibo Message was deliberate, Earth continuously leaks signals into space via TV broadcasts and radio waves. These emissions make our existence detectable to any advanced alien listeners.
Since the message was sent, over 5,000 exoplanets have been identified in the cosmos, including potentially habitable ones. Our understanding of where life might exist in the cosmos has significantly deepened.
Scientists estimate that four stars will receive the Arecibo Message within its first 500 years of travel, starting with a star known as Gaia DR3 1328057940089589376, located approximately 395 light-years away.
In 2018, Arecibo scientists held a competition to create an updated transmission. Undergraduate students from Puerto Rico’s University of Mayaguez drafted a more detailed transmission, which included a galactic map, physical constants, and schematic updates.
The new design echoed the 1974 version, sticking to binary code and schematic simplicity while modernizing details like excluding Pluto and adding key cosmic landmarks like Saturn’s rings. Interestingly, the biological data of life on Earth was omitted.
Teegarden’s Star, a mere 12.5 light-years away, was selected as the destination for the updated message. With potentially habitable planets, a reply from this system could arrive within 25 years.
In 2020, the Arecibo Observatory collapsed due to structural damage caused by Hurricane Maria. Its loss marked the end of an era for radio astronomy and interstellar communication.
For Puerto Rican scientists and students, Arecibo was a gateway to the stars, and its collapse disrupted a scientific cornerstone of the community. However, plans are underway to transform Arecibo’s site into an educational center so that its contributions to astronomy and science will inspire future generations.
The legacy of Arecibo and its message is truly an apt reflection of the deep yearning that humanity has in understanding our place in the cosmos. As technology, creativity, and imagination continue to thrive on Earth, we can only hope that our cosmic neighbors will be willing to say hello in return.
Sources: (National Geographic) (Scientific American) (History.com)
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In November 1974, humanity reached out to the cosmos with its first deliberate interstellar message. The encoded transmission, crafted with care, curiosity, and a touch of boldness, has yet to reach its intended destination. Yet, this groundbreaking act is a true symbol of our yearning to connect with intelligent alien life. Decades later, the Arecibo Message remains a cornerstone of humanity’s search for life in the cosmos.
Where did scientists send this message? What exactly did they put inside it? And can we expect to receive a response? Click through this gallery to find out.