In fact, the subject was still considered up for debate as late as 1916. To put that in perspective, electric lights, radio, powered flight, and mass produced automobiles had all been invented before most astronomers conceded that we are almost certainly alone in our solar system. Given the widespread belief in the existence of a planetary scale civilization right next door, it is hardly surprising that many astronomers and mathematicians of yore attempted to devise a way to say hello.

The first scientific proposal for contacting extraterrestrials is widely attributed to the German mathematician Carl Friedrich Gauss, who suggested creating a giant visual proof of the Pythagorean theorem in the early nineteenth century. This visual proof consists of a right triangle bordered on each side by a square and Gauss suggested it should be writ large on the surface of the Earth so that it could be seen by aliens he believed inhabited the moon. To do this, he proposed creating an outline of the squares and triangle using trees and filling the inside of the shapes with wheat.

Gauss’s plan for interplanetary communication was elegant for its simplicity, and information rich. Not only would it indicate that Earthlings had a basic grasp on geometry, it would also demonstrate our capacity for large-scale agriculture. Gauss’s plan is as forward thinking as it is absurd, but it nevertheless inspired other scientists to begin thinking about how to overcome the challenges of interplanetary communication. Later in the nineteenth century, for instance, the Austrian astronomer Johann von Littrow suggested digging huge trenches in the Sahara Desert in the form of various shapes. These trenches would be filled with water and oil would be dumped on their surface. Each night, the oil in the trenches would be set alight to send flaming messages to our extraterrestrial neighbors.

Suffice it to say, neither Gauss’s nor von Littrow’s plans for drawing shapes on the surface of the Earth ever came to fruition, but one of Gauss’s inventions did catch the attention of later would-be alien hunters. In 1821, Gauss invented the heliotrope, which used a mirror to reflect sunlight in order to send signals over several miles. The device was rapidly adopted by land surveyors, but Gauss also recognized its potential for interplanetary communication. He described an array of sixteen mirrors that could use sunlight to flash messages toward the moon in an attempt establish contact with any extraterrestrials that might live there, a feat that Gauss estimated “would be a discovery greater than that of America.”

Gauss never got a chance to test his mirror array before his death in 1855. But only a few decades later the idea was revived by scientists in France, whose free flowing ideas about methods for sending a message to extraterrestrials turned Paris into the intellectual capital of interstellar communication. In 1874, the eccentric French inventor Charles Cros petitioned the French government for funding to build a giant mirror that could burn messages into the surface of Mars as a means of communicating with Martians. Cros never received funding for his ambitious plan, but he didn’t stop petitioning the government until his death in 1888.

The dream of using mirrors to communicate with Martians didn’t die with Cros, however. A French astronomer who went by A. Mercier published a booklet titled Communication with Mars in which they outlined a plan to coat the Eiffel tower in mirrors. As the sun set each night, these mirrors could be turned toward Mars and used to send signals to the Martians.

By the end of the nineteenth century, “Mars fever” was in full swing in Europe, due in large part to the Italian astronomer Giovanni Schiaparelli announcing that he had discovered “canals” on the Red Planet. To spur scientists to focus on interstellar communication, Clara Gouget, a member of Parisian high society, established a prize in her will that awarded 100,000 francs (about $500,000 dollars today) to the first person to make contact with extraterrestrials on another planet. Notably, communication with Mars was not eligible for the prize because Gouget considered the existence of life there to be “sufficiently well known.” (The prize was eventually awarded to the Apollo 11 astronauts in 1969.)

For all the ingenuity of these early attempts at interplanetary communication, the advent of radio technologies quickly made optical schemes for extraterrestrial communication obsolete. In 1899, the Italian inventor Guglielmo Marconi transmitted the first message—a single letter—across the English channel by radio, demonstrating for the first time that “wireless telegraphy” was  commercially viable. That same year, Nikola Tesla, who was also gaining fame for his own experiments in wireless technology in the United States, recorded in his notebooks that he had received an interplanetary radio message.

Clearly, Tesla realized the power of radio for interplanetary communication, even if the signal he received from Mars was likely produced by storms on Jupiter. Marconi also recognized the power of radio for communicating over interplanetary distances and throughout the early 20th century the popular press, including the New York Times, spread rumors that Marconi was possibly sending messages to Mars. Although Marconi never admitted to trying to communicate with Mars, he did acknowledge that it was possible in principle. As Marconi told the Electrical Standard in 1906, “in 10 years, probably much less, the world will be able to send messages to Mars directly and unhesitatingly, without a hitch or a stop or a word lost in space.”

Although Marconi was a little off on his timeline, his prediction about the importance of radio for interplanetary communication was remarkably prescient. To this day, almost every spacecraft has communicated with Earth using radio (the notable exception being a handful of experiments using laser communication that NASA conducted over the past decade). The only problem for Marconi and his contemporaries was, if there were any extraterrestrials on our neighboring planets, they didn’t seem very interested in talking.

In 1932, Karl Jansky made a serendipitous observation of radiation coming from the Milky Way galaxy. Overnight, the entire universe had been transformed into a fertile hunting ground for extraterrestrial life. Although it would be another thirty years before Frank Drake launched the first microwave search for extraterrestrial intelligence at the Green Bank observatory, astronomers at least knew that interstellar communication was possible. For the last half-century, every message humans have broadcast into space, with the exception of the Pioneer plaques and the Voyager golden records, have used radio waves as their communication medium. This isn’t to say that stranger ideas haven’t been proposed.

In 1971, astronomers from the United States and the Soviet Union held the first joint conference on communicating with extraterrestrial intelligence. This meeting was attended by some of the brightest minds from both sides of the Iron Curtain, including Iosif Shklovsky, Carl Sagan, Frank Drake, and Marvin Minsky. The meeting was to discuss plans for interstellar communication, and the future of SETI. Given the creative brain power in the room, it’s hardly surprising the participants hit on some pretty wild ideas for establishing contact with ET.

In a sign of the times, the astronomer James Elliot, who would later discover the rings of Uranus, proposed blowing up the entire world’s stockpile of nuclear weapons simultaneously on the far side of the moon, as a method for signaling extraterrestrials. Based on an analysis of Starfish Prime, the largest nuclear detonation to ever occur in space, and the size of the American and Soviet nuclear stockpiles, Elliot estimated that a blast on the moon could be detected up to 190 light years from Earth. This would require a method for directing the radiation from the blast and would also require any extraterrestrials to be observing Earth at the time of detonation. Elliot conceded this made it a less than practical proposal.

Marvin Minsky, one of the progenitors of artificial intelligence, also had a novel suggestion for interstellar communication. Rather than sending images of life on Earth like, say, a photo of a cat, Minsky suggested it would be better to send the cat itself. Minsky wasn’t suggesting that we launch one of our furry friends into space, of course. Instead, he suggested using computer technology to represent various aspects of life on Earth. This could take the form of a cat simulation, or perhaps sending the genome of a cat, a human, or other animals. If aliens have more sophisticated cloning technology than our own, this DNA could act as a sort of blueprint to recreate a living version of a species, which could then be studied in vivo on the alien’s own planet.

To this day, scientists are exploring novel solutions for interplanetary communication. Laser beacons, neutrino beams, and fleets of thumb nail-sized nanocraft propelled by lasers have all been recently proposed as potential ways to overcome the so-called “great silence.” Perhaps the universe is awash in extraterrestrial communication that uses a technology we haven’t discovered yet. We’ll never learn how to pick up the phone, however, unless we challenge conventional modes of communication.

And if the strange history of interstellar communication can teach us anything, it’s that even the most outlandish proposals for calling ET might contain the seed of a practical plan.

This essay was adapted from Extraterrestrial Languages, a forthcoming book from MIT Press.