First article about the Pioneer Plaques published exactly one week before the launch of Pioneer 10.

The creation of the Pioneer Plaques was later recounted by Carl Sagan in this book.

An early account of the moment that Eric Burgess conceived of the Pioneer Plaques. The phrase "interstellar cave painting", which is often used to describe the Pioneer Plaques, probably originated with this book.

This book contains a more detailed account of the moment that Eric Burgess conceived of the Pioneer Plaques, recounted by the man himself. According to Burgess, he was informed by a NASA official that one of the plaques had been affixed to Pioneer 10 in mid-December, which means they were created during a three-week period that spanned from late November to mid-December. Burgess also writes that he did not want the plaques to include "the name of a president, or the names of politicians" because it would be "quite meaningless in a cosmic context." Considering that this book was published a few years after the launch of the Voyager probes, which included a greeting written by then President Jimmy Carter and the names of nearly a hundred members of Congress, this was probably a subtle dig at the Golden Records.

Frank Drake briefly recounted the creation of the Pioneer Plaques in the second chapter of this book that is otherwise about the Golden Records. While Drake recalls workshopping the plaques' design with Carl Sagan at a December 1969 meeting of the American Astronomical Society in San Juan, Puerto Rico, that meeting was actually held in December 1971.

The creation of the Pioneer Plaques as recounted by Frank Drake two decades after the launch of Pioneer 10. Drake once again misremembers the date when he and Carl Sagan conceived of the plaques' design. But he also includes some interesting new details, like how the addition of the plaque required "a major reanalysis of much of the design of the spacecraft" because it would "change Pioneer 10's center of gravity and its mass."

In this otherwise unrelated article, scientist and journalist Jerry Pournelle writes in a parenthesized off-hand remark that he "was there when [Burgess] got the idea" to attach a message to the Pioneers.

This is an article by and on the website of skeptic and debunker Gary Posner regarding various conspiratorial claims made by Richard Hoagland. It's primarily about Hoagland's belief that NASA is hiding evidence of a civilization on Mars, but it briefly deals with his claims to have played a more pivotal role in the conception and creation of the Pioneer Plaques. Posner spoke with Eric Burgess, Carl Sagan, Frank Drake, and Jerry Pournelle, and they all refuted Hoagland's claims. The article was originally published in Skeptical Inquire magazine in 2000, but this online reprint has since been revised and updated several times.

To accurately measure the pictograms on the Pioneer Plaques, I needed a front-facing photograph with a flat perspective. While there are a few such photographs floating around online, they are either too low-quality or mere facsimiles with subtle differences (see reference #6). Fortunately for me, there were actually three plaques produced back in December 1971 because NASA originally planned to launch three Pioneer probes. When the third mission was canceled, the nearly finished probe (along with its plaque) was handed over to the Smithsonian National Air and Space Museum in Washington, D.C. I have referenced a close-up shot of this third plaque here. The image has a resolution of 5486x3622 pixels. The large sketch of the Pioneer probe is 2331 pixels tall, the male figure is 1620 pixels tall, and the female figure is 1512 pixels tall. If 2331 pixels on the image is equal to 274.32 cm in real life, the relative height of the man (274.32 * 1620 / 2331 = 190.65) is about 191 cm, and the woman about 178 cm. If 2331 pixels on the image is equal to 260 cm in real life, the relative height of the man is about 181 cm, and the woman about 169 cm.

Photographs and information about the Pioneer 10/11 replica housed at the Smithsonian National Air and Space Museum in Washington, D.C. The eighth photograph from the top shows the spacecraft from the front, and illustrates the peculiar non-circular shape of the main reflector dish. The diameter (major axis) of the dish is said to be 9 ft or 274.32 cm, which is consistent with official NASA sources.

I made this quick side-by-side comparison to illustrate the difference between orienting the probe sideways along the major and minor axes. When oriented along the major axis, all three high-gain antenna support struts upholding the feed assembly and medium-gain antenna are visible. This is how the plaque sketches are oriented, which makes the relative height of the woman approximately 178 cm. When oriented along the minor axis, only two antenna support struts are visible. Had this been the orientation of the plaque sketches, the relative height of the woman would've been approximately 169 cm.

This early article about the Pioneer Plaques states the two horizontal lines along the right edge demarcate "the height of the human beings" even though they only demarcate the height of the female figure alone.

In this book by Carl Sagan, he writes that they only had "three weeks for the presentation of the idea, the design of the message, its approval by NASA, and the engraving of the final plaque." He also writes that the two horizontal lines along the right edge demarcate "the height of the Pioneer 10 spacecraft" even though they actually demarcate the height of the female figure standing in front of the probe sketch.

Frank Drake writes that Linda Salzman Sagan drew the couple on the Pioneer Plaques to be "of average height".

NASA's Director of Planetary Programs during the launch of Pioneer 10 and 11 was a man named Robert Kraemer. In this book of his from 2000, he wrote that the profile view of the Pioneer spacecraft drawn behind the couple on the Pioneer Plaques was "added at the suggestion" of chief engineer Robert Nunamaker (nicknamed Skip) to provide a "yardstick for the height of two human figures". This might suggest the probe sketch was a last-minute addition that didn't receive as much attention as other parts of the plaque.

The cited page (based on PDF page count) contains two technical side-view drawings of Pioneer 10. The first sketch is drawn along the major axis and shows all three high-gain antenna support struts. The second sketch is drawn along the minor axis and only shows two of the high-gain antenna support struts.

Table 9 of this article by the CDC (the national public health agency of the US) covers the mean height of American men and women between 1971 and 1974. The mean height of 4992 males between the ages of 20 and 74 was 175.1 cm. The mean height of 7919 females between the ages of 20 and 74 was 161.6 cm.

This book contains a photograph of one of the original Pioneer Plaques. However, the image quality is quite poor in the copy of the book that I have. See reference #5a for a close-up shot of the third unused plaque or reference #6a below for a high-resolution photograph of Carl Sagan holding one of the three original plaques.

About halfway through this article, there's a photograph of Carl Sagan holding one of the three original Pioneer plaques. Based on other sources, this picture was taken by photographer Jeff Albertson at City Hall Plaza in Boston sometime in March 1972. Since one of the plaques is known to have been attached to Pioneer 10 sometime in December 1971 (see reference #3d), and the probe was launched into space on March 3, 1972, the plaque shown in this picture must be the one attached to Pioneer 11 or the spare seen in reference #5a. I'm including a reference to this photograph here because it is one of the few high-quality images that I could find online that indisputably depicts one of the original plaques.

This photograph is shown at the top of the Pioneer Plaques' Wikipedia page as well as many official NASA pages. It purportedly depicts one of the original plaques. However, this is actually a facsimile used to create a postage stamp (see reference #6e below). Not only has the second bit in the binary representation of the number 8 (|---) along the right edge been sliced in half so it looks like two dots (|··--), but all the lines suffer from very noticeable ink-bleed. This would obviously not happen if the lines were physical depressions carved into metal. It's most noticeable in the center of the pulsar map, which looks like an amorphous blob instead of a fine point meant to represent the Solar System. In fact, the bleed is so severe that the beginning of one of the pulsar lines shooting off towards the northeast (PSR B1929+10; it's the second pulsar counting counter-clockwise from the galactic center line) isn't even visible in this image. In the original, uncropped, and more evenly exposed version of this photograph (see reference #6d below) you can also see the left and right edges of the plate upon which the illustrations have been drawn. The left and right margins on the original Pioneer Plaques were much wider and had two screw holes on both sides.

This is the raw photograph of reference #6c above.

These four images were originally hosted on NASA's Ames Research Center Photo Library. However, it seems that service has since been taken down because all links now redirect to NASA's Image and Video Library. Fortunately, I saved local copies of the images and have shared them here via Google Drive. I could not find these images hosted anywhere else (they were never archived either), so the only way to confirm their authenticity for the time being would be to contact NASA directly. The filename of the first image was AC72-1338, and it's the same as reference #6d above (with a slightly different tint). The filenames of the other three were AC72-1338-1, AC72-1338-3, and AC72-1338-4. I can't recall if there was an AC72-1338-2, but I don't have it either way. As confirmed by the images' EXIF metadata, AC72-1338-1 and AC72-1338-4 were captioned, "Artwork for proposed US postage stamp of Pioneer 10 plaque originally designed by Drs. Carl Sagan and Frank Drake, the plaque artwork was prepared by Linda Salzman Sagan, and mounted on spacecraft." AC72-1338-4 also carried the title "Description of Artwork Proposed for Pioneer 10 Stamp". While AC72-1338 and AC72-1338-3 were simply titled "Pioneer F/G Plaque: Pioneer 10", and made no mention of being stamp-related, all of their illustrations and imperfections are identical to AC72-1338-1. It's possible that this is the source of the mixup because all four images were scanned a few minutes apart on Jul 21, 1995, according to their EXIF metadata. It's possible the NASA archivist who made these scans assumed AC72-1338 and AC72-1338-3 depicted the original plaques, and didn't realize all four images were from the same source. All of them carry the dateline January 31, 1972, although that might be a guess based on the mistaken belief that some of them depict the original plaques.

The updated pulsar map created by Scott Ransom can be viewed on this page.

In this article, collaboratively authored by Carl Sagan, Linda Sagan, and Frank Drake, they acknowledged that "there is a negligible chance that Pioneer 10 will penetrate the planetary system of a technologically advanced society." But they also hoped that a more advanced civilization would be able to detect "an object such as Pioneer 10 in interstellar space, distinguishing it from other objects of comparable size but not of artificial origin, and then intercepting and acquiring the spacecraft." Due to the enormous distances involved, they did not foresee "any conceivable danger in indicating our position in the Galaxy, even in the eventuality, which we consider highly unlikely, that such advanced societies would be hostile."

In a chapter about Pioneer 10, Carl Sagan wrote, "In the next 10 billion years, Pioneer 10 will not enter the planetary system of any other star, even assuming that all the stars in the Galaxy have such planetary systems." He added that it is "conceivable that the spacecraft will be encountered by an extraterrestrial civilization only if such a civilization has an extensive capability for interstellar space flight and is able to intercept and recover such silent space derelicts."

In the opening chapter of this book, Carl Sagan wrote that the Pioneer probes "are condemned to wander passively and forever in the depths of interstellar space." However, he followed that up with, "Or at least probably forever. The chance of Pioneers 10 and 11 entering another planetary system in, say, the next 10 billion years, is tiny, even if every star in the Milky Way galaxy has planets." Speaking more generally about messages aboard interstellar probes, Sagan later added that they "could be received only by a civilization able easily to traverse the spaces between the stars."

When asked whether the Pioneer probes might attract hostile aliens in this press interview, Carl Sagan responded, "I don't think there's any physical threat from other intelligences in the universe. They're too far away to hurt us. But apart from the distance factor, I believe that beings from older civilizations have already learned to live with themselves and others."

In this newspaper article about the Pioneer Plaques, columnist Otto Knauth writes, "The Sagans considered the possibility that the Pioneer 10 plaque might lead a hostile civilization to conquer Earth. They rejected it, reasoning that such an interception would be so far in the future as to be beyond reckoning with."

This article contains the most detailed explanation of the Arecibo Message by the people responsible for its creation and transmission.

This is an article about the RuBisCO Stars Message (see reference #103) that was transmitted using the Arecibo Telescope in 2009, a few days shy of the 35th anniversary of the Arecibo Message. But in the comments, author Dave Dreamer relayed parts of an email that he received from Frank Drake in response to the article. Drake wrote, "Carl Sagan was not involved in any way in the construction and sending of the Arecibo message. This can be checked by going to the original publication describing the message in Science. Other staff members at Arecibo were involved, as noted in the publication, but not Carl."

A blog post by Richard Isaacman who contributed to the creation of the Arecibo Message.

This is an enlarged one-to-one recreation of the original bitmap created by Frank Drake and others. The original bitmap had a resolution of 23x73 pixels. I have enlarged the one provided here by 40 times for a resolution of 920x2920 pixels to make it easier to see.

According to this article jointly written by those who participated in the creation and transmission of the Arecibo Message, the chosen frequency, duration, and target makes it "very unlikely to produce interstellar discourse in the foreseeable future." Instead, the message "was intended as a concrete demonstration that terrestrial radio astronomy has now reached a level of advance entirely adequate for interstellar radio communication over immense distances."

Carl Sagan described the Arecibo Message as "not so much a serious effort at interstellar communication as a demonstration of the great powers that radio technology has put at our command." Frank Drake writes that the bitrate of the Arecibo Message (10 bits per second) was partially chosen "because such a signal would sound pleasing to the dedication audience." Furthermore, he limited the length of the message to 1679 bits (168 seconds or 2.8 minutes) as "more might be boring" to the attendees.

Frank Drake writes that the Arecibo Message was limited to 1679 bits because "a longer message, I feared, might get boring for the dedication audience." Regarding the selection of Messier 13 for the transmission target, Drake wrote, "It seemed we'd get the most mileage out of the message by aiming for a part of the sky where the stars were thickest. I looked at some sky charts and found that at about 1:00 P.M. on the day of the dedication, which was the time set for our ceremony, a dense cluster of some three hundred thousand stars (and possibly as many planets) would be nearly over our heads." But the fact that M13 is about 24 000 lightyears distant did not dampen his enthusiasm in the slightest because it was "a cosmic enterprise and could operate on a cosmic time scale."

Donald Campbell was among the attendees at the ceremony when the Arecibo Message was transmitted in 1974. In this 1999 article, he stated, "It was strictly a symbolic event, to show that we could do it."

A survey of 34 091 stars in the center of a globuluster known as 47 Tucanae (47 Tuc) failed to detect any Jupiter analogs in close orbits. The authors assumed this null result was because "the low metallicity and/or crowding of 47 Tuc interfered with planet formation, with orbital evolution to close-in positions, or with planet survival."

The abstract of this paper reads, "Regions of the Milky Way least likely to contain Earth-mass planets are the halo (including globulusters), the thick disk, and the outer thin disk." The paper goes on to say that the preponderance of metal-poor stars (stars that lack elements heavier than hydrogen and helium) in the galactic halo makes it "very unlikely to contain habitable terrestrial planets."

According to this journal article, the density of stars in globulusters would likely destroy or eject a planet that formed beyond 0.3 au of its parent star. For comparison, the mean distance between Earth and the Sun is 1 au while the mean distance between Mercury and the Sun is about 0.4 au.

While the prevailing view is that globulusters are unlikely to harbor life as we know it, there are a great many unknowns that could shift that perspective in the future. By making some optimistic assumptions and charitable interpretations of the scant evidence available, the authors of this journal article concluded that "several lines of reasoning suggest that globular cluster planets may be common." However, they also acknowledged that "there are many open questions about planets, the formation of life, the nature of intelligence, and the development and lifetime of advanced civilizations."

This is a database maintained by NASA of all confirmed and candidate exoplanets to date. As of the writing of this footnote, 6013 planets have been confirmed while 7699 candidates await confirmation.

This is a paper about a Jovian exoplanet in a circumbinary orbit around a pulsar and white dwarf pair with the designation PSR B1620-26 that's located in Messier 4, which is the closest (~6000 ly) globuluster to the Solar System.

This paper recently announced the discovery of an exoplanet roughly three times the mass of Jupiter in orbit around a pulsar with the designation M62H that's located in the Messier 62 globuluster near the galactic center.

The Arecibo Message was transmitted at a central frequency of 2380 MHz (10 Hz bandwidth) and an effective radiated power (ERP) of 3 TW. According to the article, "A radio telescope in M13 operating at the transmission frequency, and pointed toward the Sun at the time the message arrives at the receiving site will observe a flux density from the message which will exceed the flux density of the Sun itself by a factor of roughly 10⁷. Indeed, at that unique time, the Sun will appear to the receptors to be by far the brightest star of the Milky Way." However, the article neglects to estimate the size of the receiving telescope required to detect such a signal. Separately from the Arecibo Message, the article also states that the transmitter had a peak ERP of 20 TW, and that such a signal would be "detectable by radio telescopes of the order of sensitivity of the Arecibo instrument throughout the Milky Way Galaxy." Many sources have confused the peak 20 TW ERP of the telescope with the 3 TW ERP used to transmit the Arecibo Message. Even Drake wound up making that mistake many years later (see page 183 of reference #27c below). Another source of confusion is output power. While there's no explicit mention of output power in the article, other primary sources (e.g. reference #20) make it clear that the S-band (2380 MHz) transmitter had an average output power of 450 kW (and a peak output power of 2.5 MW). Working backwards from the stated ERP of 3 TW, an output power of 450 kW is perfectly consistent. See reference #124 for more information on this.

An interview with Frank Drake about his time as Director of the National Astronomy and Ionosphere Center and the Arecibo Radio Observatory. Questions about the Arecibo Message start and end at the cited timestamps. Furthermore, at 01:14:30, they show a photograph of Drake, Bridget Davis, and congressman John William Davis (from left to right) taken during the ceremony.

Shortly after the 40th anniversary of the Arecibo Message, Frank Drake's daughter Nadia Drake wrote this article about it for National Geographic. She also included a recording of the audible version of the message that was played in tandem with the radio transmission (see reference #27f below).

In this book published just a few years after the Arecibo Message was transmitted, Frank Drake wrote that "a few scientists" had grown concerned that the message would miss Messier 13 because he "hadn't corrected for the speed of the Earth in space in launching the message." Drake goes on to explain, "This speed is enough to divert the course of the message significantly, through an angle about one-tenth the diameter of the moon. We should correct for this. But we don't know our speed through space sufficiently accurately to make a very exact correction. In this case, it doesn't matter because the angular size of Messier 13 is larger than that of the moon, and so the message will arrive at Messier 13 even though we didn't launch it in quite the right direction."

In this article published by Cornell University shortly before the 25th anniversary of the Arecibo Message, the author repeats the misconception that it will miss its target by writing, "Ironically, the globular cluster at which the signal was aimed won't be there when the message arrives. It will have moved well out of the way in the normal rotation of the galaxy."

This is an article about the RuBisCO Stars Message (see reference #103) that was transmitted using the Arecibo Telescope in 2009, a few days shy of the 35th anniversary of the Arecibo Message. But in the comments, author Dave Dreamer relayed parts of an email that he received from Frank Drake in response to the article. Drake wrote, in part, "Every few years someone, again carelessly, challenges the 'technical correctness' or similar words of the Arecibo message on the basis that the space motion of M13 would carry it out of the beam of the transmission during the 25 000 (more accurately now 21 000) year time of transit. Thus it would miss its target." He then goes on to refute those claims.

In this article written by Frank Drake's daughter, she writes, "Some people, Dad notes, think the cluster will have moved in 20,000 years, and that the message will miss it. That's not true, he says. 'It will have moved a little bit, but only a fraction of the width of the beam of transmission,' he says."

According to Frank Drake, the Arecibo Message will take "25,000 years to reach the 300,000 stars of Messier 13, passing perhaps 30 other stars along the way." It's unclear what he means by "pass" in this sentence. It could mean that the signal will intersect and pass through the interior of some 30-odd star systems (unlikely). It could also mean that it will pass within a few lightyears of other stars along the way (far more likely). It's also unclear how he arrived at this figure because we knew a lot less about the galaxy and nearby stars back in 1974. The use of the word "perhaps" also makes it sound like an optimistic guess rather than an estimate based on data.

The author of this 1999 article states quite definitively, "There are stars closer to our solar system than [Messier 13], but none of them [are] in the path of the message."

In this online reprint of an article about the Arecibo Message that was first published in the Summer 2024 edition of the Air & Space Quarterly magazine by the Smithsonian National Air and Space Museum, author Damond Benningfield writes, "As the radio signal spreads out, it encounters many closer stars along the way." I reached out to Benningfield to see if this was anything more than a guess, but unfortunately never heard back.

I can't link directly to a scan of the letter sent by Sir Martin Ryle to Sir Bernard Lovell because it came with the warning: "Not to be reproduced, resold or published without permission." But the letter is housed here at the Churchill Archives Center at the University of Cambridge, and can be digitized and accessed remotely for a fee.

Regarding a letter he received from Sir Martin Ryle, Frank Drake writes, "[Ryle] wrote with great anxiety that he felt it was very hazardous to reveal our existence and location to the galaxy. For all we know, any creatures out there were malevolent or hungry, and once they knew of us, they might come to attack or eat us." Many sources have misattributed the latter half of that quote directly to Ryle, but it's actually just a paraphrased summary written by Drake.

Author Randall Fitzgerald quotes Sir Martin Ryle when he writes, "[Ryle] warned that other forms of life 'may be extremely hostile and they could use their advanced technology to plunder our resources.'" I was unable to locate the source of this quote.

Author Claudio Maccone quotes Sir Martin Ryle when he writes, "Ryle dismissed the Arecibo message by saying that 'when you are in a forest, it is better to listen than to shout'." I was unable to locate the source of this quote.

This is a report written by NASA engineer John Casani in mid-October of 1974. It's a standardized form that engineers and others used to submit concerns about an upcoming mission. This particular report is about the Voyager mission (which Casani went on to lead), and it's filed under the heading "Message to Extra-Solar-System Beings". In the form's concern field, Casani wrote, "No plans for sending a message to our extra solar system neighbors." In the recommendation field directly underneath, he wrote, "1) Coordinate with Barney Oliver. 2) Send a message." Casani is rarely mentioned in books and articles about the creation of the Golden Records, even though it would have never happened without his initiative.

This is the portal through which the document referenced above (hosted on Google Drive) can be located. The filename is "JPL036FL29_Outline of Concerns for MJS77 Final Mission and Systems Review_1974-10", and the filepath is JPLArchives > Documents > JPL Collections > JPL036, Voyager Project Records (1970-1988).

This 1967 article provides a brief overview of how the Video Converter Model 201-A by Colorado Video "downgrades tv signals to an audio bandwidth of 8 kilohertz." Colorado Video still exists today so I contacted them in the hopes of learning more about not just the Video Converter Model 201-A, but also their involvement in the creation of the Golden Records, but unfortunately never heard back.

A 1968 advert by Colorado Video in which their Video Converter Model 201-A is described as "a sampling scan converter designed to accept standard, composite TV signals and reduce the video bandwidth t[o] the audio range." The resulting audio signal had a bandwidth of nearly 8 kHz, ranging from 50 to 8000 Hz.

This book contains an interview with Glen Southworth, who founded Colorado Video in 1965. Southworth explained the process of converting the images to audio as follows: "The system used involved a standard Kodak carousel slide projector which was focused onto a high-quality black and white television camera. The output of the camera was then connected to the Colorado Video Model 201A that converted the original video to a single picture with a resolution of 240 by 512 picture elements, 256 shades of grey, and a bandwidth of approximately 8 kHz." While Southworth recalls the images were encoded at a resolution of 512x240 pixels (equivalent to an aspect ratio of 32:15), the two rectangular previews etched into the aluminum jackets have an aspect ratio of approximately 4:3, implying the images should be decoded at a resolution of 512x384 pixels. I initially assumed that Southworth must be misremembering because it seems like the images would come out looking stretched if they were decoded at a higher resolution than at which they were encoded. For instance, it seems like the calibration circle would end up looking like an oval. However, because these back-and-forth conversions concern analog signals rather than quantized digital ones, I'm probably failing to understand something here. Sure enough, after speaking with Ron Barry (see reference #36g below), he seemed to think this was done to somehow increase the bandwidth of the audio signals and improve fidelity, and wrote that "it makes a lot of sense, really." Southworth also mentioned that Valentin Boriakoff found out about the Video Converter Model 201-A from an "eight-page insert" inside a "large electronics catalog". I spent quite some time digging through archives of old catalogs and magazines trying to find this advert, but I never did.

This book covers the image-to-audio conversion process and tape-to-record transfer process in more detail than any other source. I have cited the most relevant pages here, but the whole book is a fantastic read. While author Jonathan Scott writes that a Video Analyzer Model 321 was used to perform the conversion, that is likely a mistake. According to Colorado Video founder Glen Southworth (see reference #36e above), the name of the device was Video Converter Model 201-A. As the names of the two devices would imply (corroborated by product descriptions in old adverts), the 321 was only used to perform analytical video tasks, whereas the 201-A was specifically designed for video-to-audio conversion.

After gaining access to the original master tapes used to transfer the audio-encoded images to the Golden Records, author Ron Barry used the instructions etched into the protective aluminum jackets to extract the images from the audio. It's a really amazing article, and there's an accompanying video as well that shows the results of the decoding process.

This is a really cool demonstration of a "live decoding of the voyager record" by Malte Gruber. It shows you in a very intuitive way how the images are extracted from the audio one scanline at a time.

This is a really clear and concise demonstration of how to use audio to transmit visual information, known as slow-scan television (SSTV).

As far as I'm aware, this is the only contemporary explanation of the jacket instructions.

While the sketches and general layout of this illustration were lifted from page 36 of reference #37a above, it's unclear when and by whom the version with explanatory text was created. Many sources claim it was made back in the 1970s, but the oldest version I could find is from the early 2000s (see reference #37c below), so it might not be as old as is often assumed.

I'm only including this because it might be the source of reference #37b above. The caption underneath the image is from page 37 of reference #37a above.

This page provides a detailed explanation of all the instructions etched into the aluminum jackets housing the Golden Records. However, it contains a mistake that I nearly fell for myself. Inscribed above the left corner of the first 4:3 rectangular preview of a partially decoded image are five lines. Read horizontally, it looks like 10000 in binary, which is equivalent to 16 in decimal. Author Tom Howe reasoned that this number represents bit depth. In other words, it tells us that each image is composed of 16 shades of grey (2^4 = 16; aka 4-bit). In Howe's (and my) defense, this interpretation is tentatively supported by a note (see Figure 8 on page 64 of reference #37a above) outlining an early draft of the records' contents where Frank Drake scribbled the sentence "4 bits per pixel" at the bottom. However, according to Colorado Video founder Glen Southworth (see reference #36e), the images were actually encoded with 256 shades of grey (2^8 = 256; aka 8-bit). When Ron Barry (see reference #36g) reproduced the images from the original master tapes many decades later, there was indeed sufficient detail to reconstruct 8-bit images. After speaking with Barry, he very politely pointed out to me that the five lines do not form one number read horizontally, but three numbers meant to be read vertically. In other words, it reads 1, 2, 3, creating a link with the segmented waveform displayed above also labeled 1, 2, 3. Now imagine aliens with absolutely zero knowledge of human conventions giving this a go...

Author Jonathan Scott interviewed numerous people involved with the creation of the Golden Records in this book. According to Scott, he was told by NASA engineer and Voyager project manager John Casani that the two cartridges were off-the-shelf and "cost no more than $20 for the pair." But according to science writer and Golden Records co-creator Timothy Ferris, they were about $160 total, and "were definitely ceramic cartridges, rather than magnetic." The cartridges were indeed described as ceramic in early newspaper reports.

This is a review (originally published in 2019) of reference #38b above. Towards the end of the review, author Glen Swanson writes that he contacted historians and archivists at NASA's Jet Propulsion Laboratory, but they were unable to locate any close-up photographs of the cartridges. However, I might have found a photograph that shows one of the cartridges from several meters away (see reference #38g below).

According to artist and Golden Records co-creator Jon Lomberg, they included a "diamond stylus" with each record.

This support page on the website of American audio equipment manufacturer Shure offers some surprising insight about the Golden Records cartridges. Shure refutes a rumor that they were manufactured by Shure because the company stopped selling ceramic cartridges before the 1970s. Instead, they claim that "NASA acquired commercially available Power-Point ceramic cartridges manufactured by Electro-Voice." After contacting Shure to find out more, they sent me reference #38f below.

After contacting Shure regarding reference #38e above, I received this document a few days later. It is credited to Shure's Director of Applications Engineering, Michael Pettersen, and chronicles his attempt to determine the make and model of the cartridges. While Pettersen believes it is unlikely that Shure manufactured the cartridges because they "abandoned ceramic for moving magnet technology in the late 1950s," he also acknowledges that NASA could have found "new old stock". Nevertheless, Pettersen contacted science writer and Golden Records co-creator Timothy Ferris, who responded, "I do seem to recall somebody on the project asking me whether Electro-Voice cartridges were good and I said they were." After comparing the outline of the cartridge illustrations etched into the Golden Records' aluminum jackets, and with assistance from "a veteran phonograph record mastering engineer" named Bill Pauluh, Pettersen concluded that the cartridges were probably manufactured by Electro-Voice. Pauluh specifically identified them as 1956 Electro-Voice Power-Point cartridges due to their distinctive "grip wings" near the front and "arch shaped contour". While Pettersen included an old Electro-Voice advert that shows a Power-Point cartridge with a matching front, it doesn't show the whole cartridge. So I spent some time searching for an exact match, but I never found one. If anything, I now have doubts about the Power-Point identification because every image I could find showed a cylindrical body, whereas the front-facing cartridge illustration on the jackets has a rectangular shape. The cartridge in the Electro-Voice advert provided by Pettersen also appears to be cylindrical. Furthermore, I couldn't find a Power-Point cartridge with a circular component in the rear and two rectangular notches in the center as shown in the top-view jacket illustration. While it's possible the jacket drawings look a bit different from the real cartridges, that seems doubtful because the whole point is for an alien to draw a parallel between the two using nothing more than visual cues. However, I am not an expert on any of this, and it's possible I simply failed to find a Power-Point cartridge (or any other model for that matter) that more closely resembles the jacket illustrations. Towards the end of the document, Pettersen also deemed it unlikely for a ceramic cartridge to remain functional after "an eon in space" because it would probably "lose its piezoelectric ability." However, it could still function as a passive carrier of the stylus (see reference #35 for a simple explanation). While cartridges are designed to translate the physical vibrations of a stylus into an electrical signal that can then be amplified and fed through a sound system, it's ultimately the stylus running through the grooves of the record that produces the sound. The vibrations could just as easily be amplified acoustically using nothing more advanced than a horn, much like an old gramophone. So as long as the aliens figure out how to spin the record and where to place the stylus, there's still a non-zero chance they could figure out how to listen to it.

In this image taken by NASA at the John F. Kennedy Space Center in 1977, you can clearly see what Carl Sagan described as "the spider support." It's the circular metallic bracket that was used to fasten the Golden Records to the Voyager spacecraft. Near the center is a small object that appears to be clamped to the bracket. The photograph is too low resolution to be certain, but it looks like it could be the cartridge and stylus. I couldn't find this photograph hosted on a NASA-affiliated website, so I've referenced a copy uploaded to Google Drive here instead. Some sources indicate the photograph was taken on July 29, 1977, while others say it was taken on August 4, 1977, and I'm unsure if the featured spacecraft is Voyager 1 or 2.

This is the most authoritative source on the contents of the Golden Records, although a few smaller details have since been updated, like the names of previously unknown artists (see reference #39c below). There's a lot of confusion about how many languages were represented on the records. Sources will list anything from 50 to 60 languages, with the most commonly quoted figure being 55. Even the authors of this book couldn't seem to agree on a count, with the opening table of contents stating there are 54 languages while the text repeatedly says there are 55. There are at least three reasons for this confusion. First, some sources make a distinction between human and animal languages because the "language" of whales can also be heard on the records. Second, some sources mix up the number of greetings with the number of languages. Third, and most significantly, the greetings were arbitrarily divided into three groups: the one recorded by then Secretary General of the United Nations (see page 26), those recorded primarily by students and teachers at Cornell University (see pages 134-143), and those recorded by other members of the United Nations (see Appendix B on pages 250-252). If we ignore animal sounds, group one consisted of 1 greeting in 1 language, group two of 55 greetings in 55 languages, and group three of 15 greetings in 12 languages. Accounting for overlap between the three groups (six greetings were in English, two in Swedish, etc.), the Golden Records contain a grand total of 71 greetings spoken in 58 different languages. There's similar confusion about the number of images. One reason for this is that color photographs were encoded as three sequential black-and-white images (one each for red, green, and blue). Another reason is that a speech by then President of the United States, Jimmy Carter, along with a list of names of 94 members of Congress, was submitted at the eleventh hour, and had to be subdivided into multiple images due to their length. If we treat the three-part color photographs as one each, there were 116 images (96 in black and white, 20 in color) selected by the Golden Records team. Meanwhile, the presidential speech and congressional list were split into six images. So the Golden Records contain a grand total of 122 images. The 118 figure mentioned in this book is only true if you count the presidential speech and congressional list as two complete images, and disregard the fact that they were split into six pieces.

Appendix A of this book is probably the most complete list of contents on the Golden Records. According to author Jonathan Scott, "no one seems sure" of the exact placement of two images containing a speech by then President of the United States, Jimmy Carter, and four images listing the names of 94 members of Congress. These six images were added very late in the records' creation, separate from the rest. However, I think it's quite clear (see the unnumbered page just before the table of contents of reference #39b above) that they were placed in between the brief Cavatina interlude near the beginning, and the greeting by then Secretary General of the United Nation, Kurt Waldheim. In fairness to Scott, he does acknowledge the possibility that they were "placed right at the start, before Kurt's spoken words." While I have only cited the most relevant pages here, this whole book is worth reading if you're interested in the contents of the Golden Records.

This is a really cool website where you can listen to all the sounds and music and view all the images on the Golden Records using an intuitive interface.

According to the caption of this photograph of the plaque on Pioneer 10, it was "attached to the spacecraft's antenna support struts in a position to help shield it from erosion by interstellar dust." The text was taken from image AC72-1338-4 of reference #6e.

Carl Sagan expected the "erosion rate in interstellar space" to be small and for the Pioneer Plaques to "remain intact for hundreds of millions of years, and probably for a much longer period of time."

Carl Sagan estimated the Golden Records would survive for at least "a billion years", but he also believed the inward-facing A side would "survive essentially forever."

The Call to the Cosmos '83 campaign was announced in the opening pages of this issue of Weekly Shōnen Jump. It was described as the "second phase" of interstellar messages, following the success of the Pioneer Plaques, Arecibo Message, and Golden Records, and proudly declared itself to be "Japan's first message to aliens."

The opening pages of this Weekly Shōnen Jump issue covers the Message to Altair with a focus on the Japanese greeting. The 48 972 original messages were placed inside a metal canister, and buried near the Stanford Dish. The burial site was also marked with a commemorative plaque (see reference #47f below). Among the technicians who carried out the transmission where Roy Basra and Roy Long. The 15 participating children were Katsuhiro Hidaka (日高 克浩), Haruya Tosa (土佐 春弥), Tomohiro Shibayama (柴山 智博), Tetsuya Yamano (山野 哲也), Shuji Kuroda (黒田 秀治), Sakakibara P.S. (榊原 追伸), Shuji Tanaka (田中 修二), Shinsuke Fujino (藤野 晋介), Akito Mogi (茂木 晃人), Masahiro Kitagawa (北川 雅浩), Koji Eno (江野 浩二), Haruki Nishiura (西浦 晴樹), Kenichi Naito (内藤 健一), Narahara Osamu (楢原 修), and Rokuhyoda Shin (六百田 真). The event was apparently covered by ABC, NBC, and CBS, and there is indeed a photograph of one of the Japanese children being interviewed by a reporter. While I was unable to find a single western source mentioning the Message to Altair back in 1983, there's probably some old news footage collecting dust somewhere.

This book was written by Hisashi Hirabayashi a few years after the Message to Altair was transmitted, and includes all 13 bitmaps along with many details that were left out of the Weekly Shōnen Jump articles. While some western sources have dubbed the initiative "Greetings to Altair", Hirabayashi called it Message to Altair (アルタイルへのメッセージ), so that's what I'm going with. It seems that, before this point, it was only known by the Shueisha campaign title Call to the Cosmos '83.

This is a book written by Hisashi Hirabayashi targeted towards a very young demographic, but it still includes some interesting details about the Message to Altair. For instance, Hirabayashi mentions that he once wrote a nine-page article about the Message to Altair titled "Searching for Companions in Space" (宇宙に伴間をもとめて) in a Japanese textbook for fifth-graders, published by Mitsumura Tosho (光村図書) between 1992 and 1999. While I found a few other references to this article, I was unable to track down a copy. The ebook I purchased has no page numbers, so the cited pages (based on page count) could be slightly off from other editions.

This Google Drive folder contains enlarged one-to-one recreations of the original 13 bitmaps created by Masaki Morimoto and Hisashi Hirabayashi. The original bitmaps had a resolution of 71x71 pixels. I have enlarged the ones provided here by 30 times for a resolution of 2130x2130 pixels to make them easier to see. The contents of the bitmaps is explained by Hirabayashi in reference #47c above, and there's a detailed explanation available on the Japanese version of Wikipedia as well. Scans of the original bitmaps were kindly provided by Shin-ya Narusawa.

Shortly before the Message to Altair was transmitted on August 15, 1983, the original 48 972 messages were placed inside a metal canister, and buried near the Stanford Dish. The burial site was marked with a commemorative plaque with information about the transmission. After contacting SRI International, senior research engineer Stephen Muther kindly provided me with a photograph of that plaque. It states, in part, "A message of peace and friendship from the children of Japan was transmitted from this location towards the star Altair in the constellation Aquila under the guidance of a group of Japanese scientists."

This is a transcript and English translation of the Japanese audio recording sent along with the 13 bitmaps. The original Japanese text was sourced from reference #47b above. The English translation was done by a person on Fiverr.

General information about Altair.

Source of high age estimate, mass, radius, temperature, metallicity, and rotation period.

Source of parallax.

This paper found that planets orbiting stars like Altair would not be exposed to as much harmful radiation as a planet orbiting a star with a slower rotation because the rotational flattening also makes the star colder and less luminous along the equator. However, even if Altair does host an earthlike planet within its habitable zone, it is unlikely to have existed long enough (~100 million years) to have spawned a spacefaring civilization.

Source of luminosity.

Source of low age estimate.

In this article published a few days before the launch of Pioneer 10 (originally published in The Washington Post), science correspondent Thomas O'Toole writes that he was told by Carl Sagan that NASA "accepted the naked couple, but objected to Linda Sagan's original drawing of the woman as being a bit too explicit." Sagan went on to explain that he "spent several days at a Telex machine, sending new versions of the man and woman to NASA's Ames Research Center in California" and that the "final version has been toned down considerably."

Carl Sagan wrote in this book that complaints about the naked couple on the Pioneer Plaques "were, on the whole, muted and few, and it hardly seemed possible to describe human reproduction while ignoring the existence of genitalia."

In this book by Frank Drake, he recalls appearing on a Canadian morning talk show shortly after the launch of Pioneer 10 to talk about the Pioneer Plaques. Even though the plaque design made some of the producers uneasy because "naked humans had never been shown on Canadian television before", the Canadian Broadcasting Company apparently "received no complains." Drake also recounts this story at 24:08 in reference #52e above.

About five months after the launch of Pioneer 10, chief engineer John Dyer attended a symposium at the Lewis and Clark College in Portland, Oregon. According to columnist Leverett Richards, during the course of the talks, Dyer joked that NASA "might decide to put clothes - or a fig leaf - on the naked figures of a man and woman on Pioneer 11" in response to "some critics who protested that NASA was exporting pornography when it placed the naked figures" on Pioneer 10.

One of the few examples I could find of a newspaper censoring the couple on the Pioneer Plaques. They've not only erased the man's genitals, but also the nipples from both of them.

An example of a newspaper headline emphasizing the fact that the couple on the Pioneer Plaques are nude. Same with the next two references below.

According to this article, associate administrator for external affairs Herbert Rowe and deputy general counsel Gerald Mossinghoff were the two NASA officials who approved the images that were etched into the Golden Records. Regarding the only rejected photograph of a naked young man and pregnant woman holding hands, Rowe said it "was not appropriate for inclusion" because they "felt that some people might get the wrong idea from the picture." Elaborating further, Rowe said, "There are some who believe that naked pregnant women are extremely erotic."

This is the earliest mention of Poetica Vaginal that I was able to find. An abbreviated version of this article simultaneously appeared in the April 2001 print issue of Scientific American (Vol. 284, No. 4, P. 40-41), but this online version is more detailed.

Brief snippets of the human-like speech can be heard in this podcast episode.

This is a radio interview with Joe Davis about Poetica Vaginal. At one point during the course of the interview, Davis "dug out an old video tape of a German television program that once did a feature on him", which included some of the human-like speech recordings. If someone could track down that program, it could very well be the first public mention of the project. An abbreviated version of this interview was originally broadcast on December 6, 2004.

This is a documentary about Joe Davis that includes a brief segment about Poetica Vaginal, during which photographs taken during the course of the project are shown. Brief snippets of the human-like speech recordings can also be heard at one point.

Russian astronomer Alexander Zaitsev briefly questioned the feasibility of Poetica Vaginal in this article.

The pre-upgrade parameters of the 26-meter Millstone Hill Radar.

The post-upgrade parameters of the 26-meter Millstone Hill Radar.

A more detailed table of the post-upgrade parameters of the 26-meter Millstone Hill Radar.

According to the introduction of this paper, there were "five antennae" at Millstone Hill in 1986.

This paper provides a brief outline of the history of the 26-meter Millstone Hill Radar.

This blog post provides a concise overview of the Millstone Hill Radar and its capabilities.

General information about Epsilon Eridani.

Source of low age estimate.

Source of habitable zone boundaries.

Source of interior debris disc boundaries.

Source of parallax.

Source of high age estimate.

Source of exterior debris disc boundaries.

This is an image showing the exterior debris disc of Epsilon Eridani, uploaded to Wikimedia by the lead author of reference #56g above.

Source of mass, radius, luminosity, temperature, and metallicity.

Source of planetary parameters.

General information about Tau Ceti.

Source of debris disc mass.

The lead author of reference #57b above stated in this interview that "it is likely that [planets orbiting Tau Ceti] will experience constant bombardment from asteroids of the kind believed to have wiped out the dinosaurs", and that "with so many large impacts, life would not have the opportunity to evolve." While another astronomer pushed back on that hypothesis by speculating that a giant planet could be "gravitationally deflecting comets and asteroids away from planets that may support life in the same way that Jupiter protects Earth", recent research suggest Jupiter is as likely to shield as it is to imperil the inner Solar System.

Source of low age estimate. However, the age is probably closer to the upper bound (see page 5 of reference #57n below).

Source of debris disc inclination, outer edge, and debris-disc-aligned planetary masses.

General information about the debris disc.

Source of stellar metallicity and overall chemical composition. The chemical composition of Tau Ceti (especially the ratio between magnesium and silicon) makes it quite different from the Sun, suggesting "the mineralogical make-up of planets around τ Ceti could be significantly different from that of Earth", which could have "a drastic impact on the rheology of the mantles of the planets around τ Ceti."

Based on the chemical composition of Tau Ceti, the lead author of reference #57g above stated in this interview that it is unlikely for any planets in the system to be habitable.

Source of debris disc inner edge.

Source of habitable zone boundaries and 90° inclination planetary parameters. The authors also noted that even though planets e and f "are located close to the boundaries of the optimistic habitable zone, their habitability might be strongly reduced by the bombardments of objects from the massive scattered disc."

Source of parallax.

This study found statistical evidence for at least four candidate planets in addition to the four that's been confirmed.

Source of high age estimate.

Source of mass, radius, luminosity, and temperature

General information about the Cosmic College event hosted by NASDA.

This page provides a timeline of the Cosmic College and many other related events.

This is a summary of a lecture held by Hisashi Hirabayashi at the 1997 Cosmic College titled "Message to ET".

This is a brief outline of the 1998 Cosmic College event titled "Let's Send a Message to Aliens!".

An article about the 1998 Cosmic College that includes an image of those who participated in the creation of that year's message posing in front of the 64-meter antenna at the Usuda Deep Space Center. The caption underneath the image reads, "This antenna was used to send a message to ETs."

This is a brief outline of the 1999 Cosmic College. According to the captions of two images (that have regrettably not been archived), a lecture about sending "messages to extraterrestrial intelligent life" was held, and they supposedly designed an image of a "leaf" to serve as "a symbol of Earth's abundant nature." While the schedule underneath the images makes it clear the students visited the Usuda Deep Space Center (from which all the previous NASDA Space Camp Messages were transmitted) the following day, it's unclear if the "leaf" image was actually transmitted.

This article briefly touched on the NASDA Space Camp Messages.

Astronomer Shin-ya Narusawa briefly mentioned the NASDA Space Camp Messages in this book. It only includes an image of the bitmap transmitted in 1995. The ebook I purchased has no page numbers so the cited pages (based on page count) could be slightly off from other editions.

Astronomer Shin-ya Narusawa briefly mentioned the NASDA Space Camp Messages in this book. It includes images of all five bitmaps known to have been transmitted. Narusawa was also kind enough to provide me with a photograph of page 89 in his own copy of this book, which included some handwritten marginalia indicating where each bitmap was transmitted. The 1995 image was sent in the direction of the constellation Libra, the two 1997 images were directed towards the star Spica, while the destinations of the 1996 and 1998 images are unknown.

This Google Drive folder contains enlarged one-to-one recreations of the original five bitmaps collaboratively designed by students who participated in the Cosmic College between 1995 and 1998. The original bitmaps had a resolution of 11x11 pixels. I have enlarged the ones provided here by 100 times for a resolution of 1100x1100 pixels to make them easier to see. These recreations are based on Shin-ya Narusawa's earlier reproductions in reference #58i above.

General information about the Usuda Deep Space Center.

According to a linked PDF document on this page titled Usuda Space Center Leaflet (臼田宇宙空間観測所リーフレット), one 20 kW klystron is used to transmit in S-band and another 20 kW klystron is used to transmit in X-band.

According to this overview of the Usuda Deep Space Center, the 64-meter antenna was outfitted with X-band receiving capabilities to accommodate the Geotail satellite and X-band transmission capabilities to accommodate the Hayabusa spacecraft.

General information about Spica.

General information about Spica.

According to this article, Spica is a supernova candidate.

Source of star A and B age, mass, radius, luminosity, temperature, semimajor axis, orbital period, and eccentricity.

Source of parallax.

While this online reprint is dated April 5, 1998, the original article was published in the April 6th issue of The Independent (page 11).

While this timeline page states Encounter 2001 was announced in March 1998, archived newspaper articles make it clear it was actually announced a month prior. It also states that two people named Alan and Debra Ladwig were the first to join the project in November. But, once again, archived newspaper articles make it clear that many thousands had joined by that point. The first people joined sometime between February and May. According to reference #61d above, the first customer was an unnamed "NASA official."

Overview of Cosmic Call I on the Encounter 2001 website.

Overview of Cosmic Call I on the Encounter 2001 website.

Overview of Cosmic Call I on the Team Encounter website.

This page lists 28 of the 43 000 messages transmitted as part of the first Cosmic Call.

Some information about Encounter 2001 project member Richard Braastad and the message he wrote for the Cosmic Calls.

This appears to be an archived press release that Encounter 2001 sent out to various news organizations shortly before the first Cosmic Call was officially announced on December 15, 1998. However, the project had already been unveiled in various news articles before this point (see reference #61).

This is a poster or summary of a presentation about the first Cosmic Call given by Yvan Dutil and Stéphane Dumas at the 193rd Meeting of the American Astronomical Society in Austin, Texas, on January 9, 1999. Figure 2 shows the 11th page of the primer, although the glyphs are from the first iteration of the language, rather than the second version that was ultimately transmitted into space. Given that this presentation was given just a few months before the first Cosmic Call was scheduled to be transmitted, the decision to shift from language version 1 to version 2 appears to have been a last-minute decision.

This appears to be an archived press release written by Yvan Dutil and Stéphane Dumas to explain the details of the first Cosmic Call primer.

An early article about the first Cosmic Call primer, written shortly before Yvan Dutil and Stéphane Dumas shifted from version 1 to version 2 of their mathematical language.

This is an article written by Yvan Dutil and Stéphane Dumas that briefly goes through both the first and second Cosmic Call.

This is a document written by Yvan Dutil and Stéphane Dumas that explains the first Cosmic Call primer in detail. The mathematical language they constructed is sometimes dubbed Lexicon (or Lexique in French) because of this document (i.e. Alexander Zaitsev in reference #64p below). However, as far as I can tell, this is merely the title of the document, not the name of the language. I could not find a single instance where Dutil and Dumas used the name Lexicon to describe their language. Instead, the name Interstellar Rosetta Stone was used to describe the updated version of the language used to write the second Cosmic Call primer (see reference #80c). As the document states, this is the second iteration of the language, designed for "more fault tolerance than the previous one." Glimpses of the first version can be seen in other references above.

This is an article written by Stéphane Dumas that explains the first and second Cosmic Call primers in detail.

This is an article written by Yvan Dutil and Stéphane Dumas that explains the first and second Cosmic Calls in detail.

When Yvan Dutil and Stéphane Dumas constructed their mathematical languages for the two Cosmic Call primers, they took inspiration from another conlang known as Lincos, invented in 1960 by mathematician Hans Freudenthal. It is sometimes reported that the Cosmic Call primers were written in Lincos, but this is not true. The language created by Dutil and Dumas is merely based upon the same fundamental ideas that underlie Lincos.

This is an interview with Yvan Dutil regarding his involvement with Encounter 2001 conducted between the first and second Cosmic Call.

This is an article written in Russian by Alexander Zaitsev. The article is more generally about METI, but the latter half is specifically about the first Cosmic Call. Zaitsev writes that they tried to alert several publications to the fact that they managed to correct the mistake on page 5 of the first Cosmic Call primer detected by Paul Houx on May 21, 1999, but that "no one cared about our 'boring' and 'uninteresting' details anymore."

This is a report written by Alexander Zaitsev and Sergey Ignatov that briefly goes through the first Cosmic Call. The BETI acronym in the title is not a typo but a rarely used precursor to METI that means Broadcast to Extraterrestrial Intelligence (see reference #86).

Some general information about the first Cosmic Call and Encounter 2001.

This is a detailed explanation of the first Cosmic Call primer by computer programmer and amateur mathematician Mark Dominus. Dominus also points out a few mistakes. For instance, the wrong glyph was used to represent a variable on page 5, Uranium is said to have 116 neutrons when they probably meant 146 on page 7, and the kilogram is incorrectly defined on page 7.

This article provides a detailed overview of the entire Cosmic Calls project.

After the first Cosmic Call concluded, Encounter 2001 sent out certificates like this one to those who participated. The seven glyphs above the telescope are curiously from the first unused version of the mathematical language constructed by Yvan Dutil and Stéphane Dumas. This is probably because they decided to shift from version 1 to version 2 just a few months before the first Cosmic Call was scheduled to be transmitted so there wasn't enough time to update the certificates.

Because Yvan Dutil and Stéphane Dumas decided to create a new version of their mathematical language just a few months before the first Cosmic Call was scheduled for transmission, they ended up making a few mistakes. For instance, in the first draft of the language, equal signs were represented by four horizontal lines stacked on top of one another. But in the second draft, a vertical line was inserted in the middle of the glyph. However, Dutil and Dumas missed two instances of the older glyph design on page 5 of the updated bitmaps. This was only noticed about two weeks before the beam-up date by a Dutch programmer named Paul Houx. While this article suggested it was too late to correct the mistake, it was in fact corrected at the very last moment (see references below).

When an article about the first Cosmic Call titled Aliens Geef Antwoord! (Aliens Answer!) was published in the May 1999 issue of a Dutch magazine known as Kijk, it caught the attention of a programmer named Paul Houx. On May 10, Houx noticed a mistake on page 5 of the Comic Call primer, and quickly alerted Yvan Dutil. With only two weeks left before the message was set to be transmitted, Dutil initially thought it was too late to correct the mistake, which is what he told a few journalists at the time (i.e. reference #64v above). However, on May 21, just three days before the first Cosmic Call was scheduled for transmission, Dutil finally managed to get in touch with Alexander Zaitsev at the Evpatoria Deep Space Center. Zaitsev and other members of the Encounter 2001 team were then able to correct the errors before the first transmission session commenced on May 24.

This is an archived article originally published on the website of a company in the Netherlands known as IJsfontein where programmer Paul Houx was employed. It's about the same mistake explained in reference #64w above, except it's written in English, and contains a few more details.

This Google Drive folder contains enlarged one-to-one recreations of the original 23 bitmaps created by Yvan Dutil and Stéphane Dumas. The original bitmaps had a resolution of 127x127 pixels. I have enlarged the ones provided here by 20 times for a resolution of 2540x2540 pixels to make them easier to see.

General information about 16 Cygi A.

General information about 16 Cygi B.

General information about 16 Cygi C.

Source of star C mass. While the authors note that an earlier paper (a 1998 preprint by Trilling et al. that does not appear to have been published online) estimated star C to have a mass of 0.4 MS, their own findings suggested a mass below 0.25 MS.

It was initially unclear if star C was bound to A, but this paper confirmed that it was.

According to this paper, a planet within the habitable zone of star B has zero chance of surviving beyond 1 million years due to the highly eccentric orbit and gravitational influence of planet Bb.

Source of projected separation between stars A and C.

The authors of this paper found that the highly eccentric orbit of planet Bb precludes other planets from maintaining stable orbits beyond 0.3 au from star B. Their results were consisted with those of reference #65f above, which found that no planets survived within the star's habitable zone.

According to this paper, a giant planet like the one that orbits star B is not expected to be found orbiting star A. However, the authors also note that the "presence of low-mass and/or long orbital period planets around either of these two stars is, of course, not to be ruled out."

Source of stars A and B semimajor axis, orbital period, and eccentricity. The authors note that an "additional 20-30 yr of high-accuracy ground-based observations of the ADS 12815 system will be required in order to unambiguously determine the orbit of this binary." However, they also note that "it may be possible to calculate a final orbit for this star in another 3-4 years time if the Gaia satellite is successfully flown". The Gaia space telescope was launched three years after this paper was published, but I could not find any more recent papers that tried to determine the orbits of stars A and B.

Source of planet Bb mass, semimajor axis, orbital period, and eccentricity.

Additional information about the ages of stars A and B.

The authors of this paper theorize that "the red dwarf that orbits 16 Cygni A may be the reason for the fact that the main star could not develop any planetary disk."

Source of stars A and B habitable zone boundaries.

The authors of this paper found it "very unlikely" that star C prevented a planetary system from forming around star A as suggested by reference #65m above. Instead, the authors concluded that "16 Cyg C at 73 AU may be too far as to have any significant impact on 16 Cyg A."

Source of star A parallax.

Source of star A high age estimate.

Source of star A low age estimate.

Source of stars A and B mass, radius, luminosity, temperature, and metallicity.

General information about Gliese 746.

According to this paper, star B is either a red or white dwarf.

Source of star A high age estimate (BaSTI expectation age) and metallicity.

Source of star B minimum mass, and stars A and B projected separation, orbital period, and eccentricity.

Source of parallax.

Source of star A low age estimate.

Due to apparent perturbations and luminosity variations, the authors of this paper suggest star A might host a large planet with a mass of 0.15 MJ, semimajor axis of 0.13 AU, and eccentricity of 0.27. However, they ultimately concluded that the fluctuations were "generated by stellar activity."

Source of star A mass, radius, luminosity, and temperature.

General information about component A.

General information about component B.

Source of component B temperature.

Source of component B radius and luminosity.

Source of parallax.

Source of component A high age estimate.

Source of component A low age estimate.

Source of component B mass, semimajor axis, orbital period, and eccentricity.

Source of component A temperature and metallicity.

Source of component A mass, radius, and luminosity.

General information about star A.

General information about star B.

According to this paper, a "two-exposure plate from 1971.42 shows a fainter star next to B", which means that Gliese 777 could be a ternary system. However the author notes that a subsequent observation made in 1973 failed to detect the star, and I couldn't find any evidence it's been detected since. It was probably just a background star, although the author adds that it "may be variable, perhaps a flare companion."

Source of star A low age estimate and habitable zone boundaries. The authors note that a "wide range of ages has been found" for star A and that its true age is highly uncertain.

Source of star A parallax.

Source of stars A and B projected separation. The authors also found tentative evidence for a third planet orbiting star A, but it is not within the habitable zone, and has yet to be confirmed.

Source of star B temperature and metallicity.

Source of star A high age estimate, temperature, and metallicity.

Source of star A mass, radius, and luminosity.

Source of star B mass, radius, and luminosity.

Source of stars A and B orbital period.

Source of planets Ac, Ad, and Ab mass, semimajor axis, orbital period, and eccentricity. The authors also found that the habitable zone of star A is stable enough to host an earthlike planet.

This is a report that Alexander Zaitsev first presented at a conference in Moscow on February 3, 2000, in which he explored the possibility of communicating with aliens using music played on a theremin. An idea that would later be incorporated into the Teenage Message.

This is a proposal that Alexander Zaitsev submitted to the National Astronomy and Ionosphere Center in July 2000, seeking to use the Arecibo Telescope in Puerto Rico to transmit an interstellar message consisting of music played on a theremin. However, the proposal was rejected (see reference #72k below).

General information about the creation of the Teenage Message.

General information about the creation of the Teenage Message.

This is an article about the Teenage Message written by Boris Pschenichner several months before the message was transmitted. At this stage, they had come up with a preliminary list of seven targets: HD 95128, HD 126053, HD 19373, HD 19994, HD 48682, HD 62613, and HD 190067. Only the first two made the final cut.

This is an archived page about the Teenage Message on the website for the Moscow State Palace of Child and Youth Creativity. Subsequent versions of the page (archived from 2003 onwards) contains additional information.

This archived page explains the different components of the main emblem of the Teenage Message. There are ten more pages like this one explaining the ten images encircling the emblem. Just replace the number in the URL to see the other pages (c0.html, c1.html, c2.html, etc.) It seems the original pages also loaded the images alongside the explanatory text, but only the text has been archived (see reference #72q for the images).

This is an online reprint of a magazine article about the Teenage Message written by Boris Pschenichner shortly before the message was transmitted.

This archived page has a lot of information about the Teenage Message, including all 28 bitmap images.

This is a detailed report about the Teenage Message that was first presented at a conference in Moscow known as SETI on the Threshold of the 21st Century (SETI на Пороге XXI Века) between February 5-7, 2002.

This is a presentation that Alexander Zaitsev gave at a conference in Paris, France, on March 2002 regarding his idea to use a theremin to play the music that was later transmitted as part of the Teenage Message.

This is a complementary article to reference #72k above.

This is a detailed overview of the Teenage Message collaboratively written by those who made it. It's especially useful because it contains a detailed list of all the music that was transmitted.

This is an online reprint of a magazine article written by Lev Gindilis that provides a detailed overview of the Teenage Message.

This is an article about the Teenage Message written by Alexander Zaitsev, with a focus on the decision to use a theremin to play the music.

Alexander Zaitsev shared six recordings of the nine musical compositions included with the Teenage Message on this page.

This Google Drive folder contains enlarged one-to-one recreations of the original 28 bitmaps collaboratively designed by those who participated in the creation of the Teenage Message between 2000 and 2001. Egor Kiselev and Vladimir Filippov were the primary authors, but others may have contributed as well. The original bitmaps had a resolution of either 101x101 or 307x307 pixels. I have enlarged the ones provided here by either 20 times for a resolution of 2020x2020 pixels or 10 times for a resolution of 3070x3070 pixels to make them easier to see.

General information about star A.

General information about stars B and C (they're often treated as one star labeled B due to their proximity). As noted on this page, Gliese 797 B (True B) should not be confused with another star designated WDS J20408+1956B (Fake B). That's because Fake B is very close to Gliese 797 A when viewed from Earth (known as an optical binary or visual double), and has occasionally been designated Gliese 797 B in the past. This has led to confusion where some sources use the designation Gliese 797 B to refer to True B while others use it to refer to Fake B. To make things even more confusing, some sources use the designation Gliese 797 C when they're actually referring to True B. Some sources also use the labels Ba and Bb (or Ca and Cb) to refer to the two stars of True B. To clear up any confusion, I use the designations Gliese 797 B and C when referring to the two stars of True B.

Source of the combined BC pair mass, radius, luminosity, temperature, and metallicity.

According to this article, two other stars (labeled D and E in this article) that are visually close to the BC pair (labeled Ca and Cb in this article) are optical binaries that are not actually bound to the system.

Source of star A low age estimate, temperature, and metallicity.

Source of star A parallax.

Source of star A high age estimate.

Source of projected separation between star A and BC pair (stars B and C are respectively labeled Ca and Cb in this article).

Source of star A mass, radius, and luminosity.

General information about 37 Geminorium.

Source of parallax.

Source of high age estimate.

Source of low age estimate.

Source of temperature and metallicity.

Source of mass, radius, and luminosity.

General information about 47 Ursae Majoris.

Source of planets b, c, and d mass, semimajor axis, orbital period, and eccentricity.

Source of habitable zone boundaries. The authors note that most of the habitable zone is stable enough to host an earthlike planet, but orbits become unstable near the outer edge due to the presence of planet b. The authors also found that comets are unlikely to have collided with planets within the habitable zone during the formation of the system. This could pose a problem for habitability because one hypothesis for the origin of Earth's water is cometary impacts. However, it's unlikely that all of Earth's water originated from comets alone (some models suggest it was less than 10%), so a lack of cometary impacts is not enough to discount water-rich planets within the habitable zone of 47 Ursae Majoris.

Source of parallax.

Source of high age estimate.

Source of low age estimate.

Source of temperature and metallicity.

Source of mass, radius, and luminosity.

General information about component A.

General information about component B.

Source of components A and B projected separation.

Source of component A parallax.

Source of component A low age estimate.

Source of component A high age estimate, temperature, and metallicity.

Source of component B mass, radius, luminosity, and temperature.

Source of component A mass, radius, and luminosity.

General information about Gliese 327.

Source of debris disc location #1.

Source of parallax.

Source of low age estimate.

Source of debris disc location #2.

Source of high age estimate, mass, radius, luminosity, temperature, and metallicity.

General information about Gliese 788.

Source of low age estimate.

Source of parallax.

Source of high age estimate.

Source of temperature and metallicity.

Source of mass, radius, and luminosity.

Cosmic Call II was initially scheduled for the second quarter of 2000.

Overview of Cosmic Call II. It was at one point scheduled for transmission on February 14, 2003. The project was then delayed to May (see subsequent archives of this page), then to sometime in July, then to July 5 and 6, before they ultimately settled on July 6.

Overview of Cosmic Call II with lots of detailed information about the mathematical language created by Yvan Dutil and Stéphane Dumas, the Evpatoria Deep Space Center, and the target stars.

Overview of Cosmic Call II with information about the different components of the message.

A detailed minute-by-minute chronology of the transmission of Cosmic Call II on July 6, 2003.

Information about the artificial intelligence program (a chatbot named Ella) that was included with Cosmic Call II.

Information about a website co-authored by dozens of SETI researchers that was included with Cosmic Call II (see reference #80h below for the actual website).

A few months before the transmission of Cosmic Call II, Team Encounter announced that one song from the David Bowie album The Rise and Fall of Ziggy Stardust and the Spiders From Mars would be included. Customers were given the option to vote on the songs Five Years, Soul Love, Moonage Dreams, Starman, It Ain't Easy, Lady Stardust, Star, Hang On to Yourself, Ziggy Stardust, Suffragette City, and Rock 'N' Roll Suicide. Five Years received 82 votes, Rock 'N' Roll Suicide received 105, Ziggy Stardust received 147, but Starman won out with 161 votes.

After the second Cosmic Call, Team Encounter planned to to transmit Cosmic Call III during the first quarter of 2004.

Two months after Cosmic Call II was transmitted, the front page of the Team Encounter Website claimed that more than 100 000 people had joined the project.

According to this timeline page, Encounter 2001 rebranded and changed its name to Team Encounter on September 9, 2000. However, the original Encounter 2001 website was not updated with Team Encounter graphics until sometime in January 2001.

At one point, Cosmic Call II was scheduled for November 15, 2001.

According to this archived timeline page from late 2001, Team Encounter originally anticipated one million customers by the second quarter of 2002 when they originally planned to transmit Cosmic Call III.

According to this article about the Millennial Voyage, 67 000 people had signed up for Team Encounter by June 2001.

This article provides a detailed overview of Cosmic Call II. It's an English translation of a Russian article that was originally published in the 2003 edition (issue 5/22-6/23) of the SETI Herald (Вестник SETI) by the SETI Scientific and Cultural Center (Научно-Культурный Центр SETI).

This article is more generally about Celestis and launching cremains into space, but it also touches upon Team Encounter. It was published just two months before the second Cosmic Call was transmitted. According to the author, some 200 000 people had signed up at this point. However, other sources (i.e reference #80k above and reference #80x below) suggest it was closer to 100 000.

This is an article written by Yvan Dutil and Stéphane Dumas that briefly goes through both the first and second Cosmic Call.

This is an article written by Stéphane Dumas that explains the first and second Cosmic Call primers in detail.

This is an article written by Yvan Dutil and Stéphane Dumas that explains the first and second Cosmic Calls in detail.

This is a page about Cosmic Call II documented by Team Encounter staff member Richard Braastad on his personal website. Braastad passed away in 2022.

More information about the artificial intelligence program (a chatbot named Ella) that was included with Cosmic Call II. It was apparently only included with the last session transmitted in the afternoon of July 6, 2003, towards Gliese 49.

This article is more generally about Celestis and Charles Chafer, but it briefly touches on the shut down of Team Encounter. According to Chafer, the project was terminated sometime in May 2003 (two months before Cosmic Call II) after its main investor pulled the plug. The unnamed investor had apparently "sunk more than $7 million" into both Celestis and Team Encounter by that point.

This article was published in response to claims that Across the Universe (see reference #96) was the first time that music had been beamed into space. But according to Charles Chafer, he secretly included the song One Love by Bob Marley with both the first and second Cosmic Call. Chafer also says that they transmitted over 100 000 messages in total.

This is an enlarged one-to-one recreation of the original bitmap created by Yvan Dutil and Stéphane Dumas. The original bitmap had a resolution of 127x2078 pixels. I have enlarged the one provided here by 10 times for a resolution of 1270x20780 pixels to make it easier to see.

General information about Gliese 67.

Source of star A and B habitable zone boundaries. This paper specifically looked at the intersection between orbital stability and habitable zones around binary systems. While the authors found that circumstellar orbits within the habitable zone of both star A and B are stable, circumbinary orbits within the combined habitable zone of both stars are not.

Source of star A temperature and metallicity.

Source of star A parallax, low age estimate, mass, radius, and luminosity; star B mass, semimajor axis, orbital period, and eccentricity.

General information about star A.

General information about star B.

Source of star A high age estimate.

Source of star A parallax.

Source of stars A and B projected separation.

Source of star A low age estimate.

Source of stars A and B mass, radius, luminosity, temperature, and metallicity.

General information about star A.

General information about star B.

Source of star A high age estimate; and planets Ae, Ab, Ac, Af, and Ad mass, semimajor axis, orbital period, and eccentricity.

Source of star A habitable zone boundaries. The authors found that orbits become unstable near the inner edge of the habitable zone due to the presence of planet Af, but an earthlike planet could maintain a stable orbit closer to the outer edge.

Source of star A parallax.

According to the authors of this paper, an earthlike planet is "very likely" to exist between planets Af and Ae. Such a planet could maintain a stable orbit between 1 and 2.6 au, although it is most likely to have formed between 1.5 and 2.1 au. Because the habitable zone of star A only extends to 1.43 au, the probability of finding an earthlike planet between 1 and 1.43 au is only about 10%.

Source of stars A and B projected separation.

According to this paper, a moon orbiting planet Af with a mass of 2.33 ME and radius of 1.57 RE has a 34% probability of being habitable.

Source of star A low age estimate, temperature, and metallicity.

Source of star A mass, radius, and luminosity.

Source of star B mass, radius, luminosity, temperature, and metallicity.

The authors of this paper found that a four-planet model that excludes the outermost planet Ad "performs at least as well as the widely agreed-upon 5-planet system". This means that planet Ad could be a false positive caused by stellar activity. However, planet Ad is still listed as "confirmed" in the NASA Exoplanetary Archive as I'm writing this footnote, so I decided to stick with a five-planet model for the video.

General information about star A.

General information about star B.

Source of star A low age estimate.

Source of star A habitable zone boundaries; and planet Ab mass, semimajor axis, orbital period, and eccentricity.

Source of star A parallax.

Source of stars A and B projected separation.

Source of star A high age estimate.

Source of stars A and B mass, radius, luminosity, temperature, and metallicity.

These are the original PowerPoint slides that Iván Almár used when he first presented the idea for the San Marino Scale at a SETI conference held in the Republic of San Marino in 2005.

An explanation of the San Marino Scale by Iván Almár and Paul Shuch.

A simple tool for calculating the risk of an interstellar message using the San Marino Scale.

Iván Almár and Paul Shuch explored a few different METI projects in this paper and ranked them according to the San Marino Scale. The Arecibo Message received a score of 8 (Far-Reaching), while the two Cosmic Calls and the Teenage Message received a score of 7 (High).

Astronomer Shin-ya Narusawa briefly touched on the San Marino Scale in this book. Translated from Japanese, he writes, in part, "I believe there is still room for revision of the San Marino scale. [...] For example, even if the same message were to be sent, the degree of risk would be different if it was sent to Altair, where the possibility of life is thought to be low, compared to sending it to Tau Ceti, a star with habitable planets. Sending it to M13, which is 25,000 light years away, may pose little to no risk. I think it is time to revise the system by taking into consideration the distance and characteristics of the star to which the message is being sent." It's also worth pointing out that Narusawa incorrectly states Iván Almár conceived of the San Marino Scale in 1995 when it was actually 2005. The ebook I purchased has no page numbers, so the cited page (based on page count) could be slightly off from other editions.

This graph shows the usage of CETI and SETI over time.

This graph shows the usage of Active SETI and METI over time.

An article by the International Academy of Astronautics that credits the coining of CETI to Rudolf Pešek.

An early example of an article using both the capitalized and lowercase phrase "communication with extraterrestrial intelligence", but not the abbreviated form.

Another early example of an article using the capitalized phrase Communication with Extraterrestrial Intelligence in the title. But it was never used in its lowercase nor abbreviated form within the body of the article.

This is a book chapter written by astronomer Frank Drake in which he outlined his 1960 SETI experiment known as Project Ozma. Some sources claim SETI was coined in this text, but Drake only used the similar phrase "search for extraterrestrial intelligent life".

An early example of the lowercase phrase "search for extraterrestrial intelligence", except it's only used once and never abbreviated. The lowercase phrase "communication with extraterrestrial intelligence" is also used once, but not abbreviated.

An early article about the CETI conference held in Soviet Armenia between September 5-11, 1971.

A book about the CETI conference held in Soviet Armenia between September 5-11, 1971, by Carl Sagan.

The SETI acronym was possibly coined during this NASA workshop held in 1976.

The reasoning behind using SETI instead of CETI is outlined in this NASA report.

This is a collection of articles about CETI assembled by John Billingham and Rudolf Pešek. In a footnote, they write, "The term CETI has been used for many years as a generic title for all aspects of Communication with Extraterrestrial Intelligence. The term SETI was introduced in the United States in 1976 to reflect the widely held view that the primary endeavor should be a Search for Extraterrestrial Intelligence." Meanwhile, in an article originally published earlier that year in the journal Acta Astronautica titled Activities of the IAA CETI Committee from 1965-1976 and CETI Outlook, Pešek wrote that he conceived of an "international symposium" regarding the existence of extraterrestrial life in 1965. He then goes on to say, "For this symposium, I devised the word CETI - an acronym for Communication with Extraterrestrial Intelligence. The choice is also connected with the well-known fact that Ceti in Latin is the genitive of Cetus (whale) and that Tau Ceti is a star 11.8 light years distant, rather similar in size and luminosity to our Sun."

In response to an earlier article about SETI, NASA scientist and member of the Planetary Society Francis Merceret wrote, "I just received my first issue of The Planetary Report and am accepting your invitation to comment on the subject of the Search for Extraterrestrial Intelligence (SETI). I do not share the Society's enthusiasm for this project. Passive SETI is unlikely to be productive, although it may be harmless enough, and active SETI is a dangerous, foolhardy undertaking." I wouldn't be surprised if these terms were used before this point, but this was the earliest example I could find.

In this report about the first Cosmic Call, Alexander Zaitsev and Sergey Ignatov coined the acronym BETI.

This is an archived page about the Teenage Message hosted on a website run by one of the organizers named Sergey Egorovich Guryanov (Сергей Егорович Гурьянов). The page clearly states the "provisional name" of the project was "METI or METI-children" abbreviated from the English phrase "Message to Extraterrestrial Intelligence". There's also a logo in the top left that says METI in all capital letters. This is the earliest use of the acronym METI that I could find.

This is the archived homepage of a Russian community center known as the Moscow State Palace of Child and Youth Creativity, which helped organize the Teenage Message. The project is advertised with the same METI logo featured in reference #86o above.

This is a list of those who participated in the creation of the Teenage Message. When the page was archived in early 2001, the title read "METI - Message for Extraterrestrial Intelligence" in English. There's some disagreement over the precise phrase that METI is abbreviating. The phrasing I prefer, and the one used by the non-profit organization METI International, is simply "Messaging Extraterrestrial Intelligence".

This is an abstract of a presentation about METI titled "METI@home Project: Radio Messages to Extraterrestrial Civilizations from Home" that Alexander Zaitsev gave at a conference in Moscow in February 2002. The presentation explored the possibility of creating a crowdsourced interstellar messaging platform similar to the SETI@home project, which had launched a few years earlier in 1999. Zaitsev posted the abstract of his presentation on this Russian astronomy forum ahead of the conference in December 2001.

This is an interview with Alexander Zaitsev in which he uses the acronym METI. It is probably the first use of METI in an English source.

Near the beginning of this article, which was co-authored by Alexander Zaitsev and Team Encounter members Charles Chafer and Richard Braastad, the trio wrote, "Today, the deliberate transmission of messages to the stars is often referred to as Active SETI, as opposed, presumably, to Passive SETI, the monitoring approach described above. Other terms have been suggested for Active SETI: BETI, for Broadcast to Extraterrestrial Intelligence, and METI, our preferred acronym, for Messaging to Extraterrestrial Intelligence."

This is a book that's more generally about SETI but includes a chapter about METI written by Alexander Zaitsev. Near the beginning of the book, Zaitsev is described like this: "Under his scientific leadership, a youth group in Moscow composed and broadcast a 'Teen Age Message to ETI'. Zaitsev proposed a three-section structure of interstellar radio messages, coined the acronym METI (Messaging to Extra-Terrestrial Intelligence) and the phrase 'SETI Paradox', which refers to an apparent paradox where two distant civilizations capable of interstellar communication will always remain silent unless one of them contacts the other first, resulting in a deadlock of silence."

According to this FAQ on the project's official website, it's not known how long the One Earth message could have survived on the New Horizon's computer memory. However, conservative estimates suggested it would have "a lifetime of a few decades." More optimistically, some believed "the message might remain for centuries or even millennia." While project director Jon Lomberg would later claim (see reference #94h below) the One Earth message "could last a million years if done right", that seems highly improbable. Longevity estimates for data stored on consumer-grade memory chips rarely exceed a decade or two. While it's conceivable that more resilient chips specifically designed for space travel by NASA could have lifespans measured in centuries or even millennia, a million years stretches believability.

Carl Sagan wrote in 1978 that it may be possible to redirect the two Voyager spacecraft towards a distant star system once they had completed their scientific mission. Others have made similar suggestions in the years since like planetary scientist Jim Bell in reference #95b below. Since the Voyagers are likely to become inoperable within just a few short years, it seems unlikely that such a maneuver will be performed at this stage, so I decided not to bring it up in the video.

A very brief article by astrophysicist and science writer Ethan Siegel about redirecting New Horizons towards a nearby star systems before its mission comes to an end.

According to New Horizons' Principal Investigator Alan Stern, projections by Mission Systems Engineer Chris Hersman suggest the spacecraft "will quite likely have enough power to take science data through the 2040s and even to 2050".

Official website promoting the Across the Universe message.

A forum thread with some information about Across the Universe posted by someone who was at NASA mission control during the transmission.

Specifications of the antenna used to transmit Across the Universe.

General information about star Aa.

General information about star Ab.

Source of star Ab low estimate semimajor axis.

Source of stars Aa, Ab, and B age range estimates.

Source of star B parallax. Due to the extreme brightness of star Aa, it's easier to derive the system's distance from the parallax of its most distant and significantly dimmer companion.

Source of star Aa luminosity.

Source of star Aa temperature and metallicity.

Source of stars Aa and B projected separation.

Source of star B mass, radius, luminosity, temperature, and metallicity.

Source of star Ab high estimate semimajor axis. The paper only specifies a periastron distance of 6.2 au. Using 6.2 / (1 - 0.6354), we get an approximate semimajor axis of 17.005 au.

Source of star Aa mass and radius; star Ab mass, orbital period, and eccentricity.

Official YouTube channel for the "You Make It, We Play It" advertisement campaign, which has all the submitted commercial entries, including the winning one called Doritos Tribe.

Press release by the University of Leicester before the transmission.

Promotional video by scientist Anthony van Eyken who oversaw the transmission at the EISCAT radar station in Svalbard, Norway.

Post on the official EISCAT website announcing the transmission.

Press release by the University of Leicester after the transmission.

Technical details about the radio telescope used to transmit the message. It's the 32-meter antenna located near the town of Longyearbyen in Svalbard, Norway. It can transmit at frequencies between 498 to 502 MHz with an average power output of 250 kW and a peak power output of 1 MW.

General information about Gliese 581.

Source of debris disc extent and mass.

According to the authors of this article (which is about reference #100b above), Gliese 581 is surrounded by "at least 10 times more comets" than what orbits the Sun.

Source of parallax.

Source of low age estimate.

Source of habitable zone boundaries.

Source of high age estimate.

Source of planet e, b, and c mass, semimajor axis, orbital period, and eccentricity. While previous studies had found tentative signs of additional planets, including two habitable zone candidates designated d and g, the authors of this paper concluded that "the system is unequivocally composed of only three planets detectable in the present data, dismissing the putative planet GJ 581 d as an artifact of stellar activity."

Source of mass, radius, luminosity, temperature, and metallicity.

This article provides a brief and easy to understand overview of the many issues faced by an earthlike exoplanets orbiting an M-type star.

This paper examines the relationship between the rotation of a terrestrial planet more massive than Earth and the strength of its magnetic field. The authors found that a slower rate of spin (i.e. tidally locked planets) will reduce a planet's magnetic field. They write that "the emergence and continued existence of a protective planetary magnetic field is not only a function of planetary mass but also depend on rotation rate." However, they also caution against assuming that tidally locked planets have no magnetic field at all. They write, "As has been shown here there are a range of periods of rotation where planets could sustain moderate magnetic fields having large periods of rotation."

This paper examined the impact of persistent stellar winds (transient events like flares and coronal mass ejections were ignored) on exoplanets orbiting very close to their star, as is the case with M-type red dwarfs. The authors found that such planets are unlikely to retain an atmospheric envelope due to their proximity to their star. Furthermore, planets orbiting within the habitable zone of M-type stars are likely to become tidally locked, "which dramatically decreases the probability that they can maintain their atmospheres."

This paper found that red dwarfs "may comprehensively destroy ozone shields and subject the surface of magnetically unprotected Earth-like planets to long-term radiation that can damage complex organic structures." However, they note that aquatic life could still survive if the planet hosts an ocean.

This paper found that tidally locked planets orbiting M-type stars "may be less hostile to life than previously thought." The authors conclude that exoplanets orbiting within the habitable zone of M-type stars "may have temperatures supporting liquid water and complex organic molecules on at least part of their surface, for a wide range of irradiation and atmospheric properties, in particular taking into account the greenhouse and circulation effects."

This paper provides a detailed overview of the impact of stellar winds, flares, and other space weather events on the habitability of earthlike exoplanets orbiting G-, K-, and M-type stars. The cited pages are specifically about the habitability of exoplanets orbiting M-type stars, but the whole paper is worth reading if you want a more in-depth understanding of the numerous factors that influence exoplanetary habitability.

While this paper is more generally about a method of M-type age determination, the cited page contains a brief summary that conveniently lists some of the positive, negative, and unknown factors regarding the habitability of red dwarf exoplanets.

Some general information about the RuBisCO enzyme.

General information about TZ Arietis.

Source of high age estimate.

Source of low age estimate.

Source of parallax.

Source of planet c mass, semimajor axis, orbital period, and eccentricity. While this paper refers to the planet as TZ Arietis b, that designation was already used by an earlier paper from 2020 in reference to a different planet candidate with an orbital period of 240 days. Instead, the 2020 paper designated this planet as TZ Arietis c. While the 240-day candidate was ultimately ruled a false positive, planets are by convention named in order of discovery (even if their existence is subsequently challenged), so the correct designation should probably be TZ Arietis c, which is how this planet is labeled in the NASA Exoplanet Archive.

Source of habitable zone boundaries.

Source of mass, radius, luminosity, temperature, and metallicity.

General information about Kappa¹ Ceti.

While Kappa¹ Ceti is a solar analog, it's still very young and therefore a lot more active than the Sun. This paper found that it spews about 50 times more mass into space than the modern-day Sun, which could negatively impact the habitability of earthlike planets (i.e. atmospheric erosion).

Source of parallax.

Source of high age estimate.

This paper identified Kappa¹ Ceti as a solitary G-type star.

Source of mass, radius, luminosity, temperature, and metallicity.

Source of low age estimate.

General information about Teegarden's Star.

Source of age range estimate. According to this paper, if there are alien astronomers searching for earthlike planets at Teegarden's Star, "the Earth will be observable as a transiting planet from 2044 until 2496."

Because the planets around Teegarden's Star have such tight orbits, they are vulnerable to atmospheric erosion by stellar winds. The authors of this paper found that planets b and c only have a 3% and 2% probability of retaining their atmospheres, respectively. They also concluded that both planets are tidally locked in a 1:1 spin-orbit resonance.

According to this paper, planets b and c are "most probably tidally locked." However, they are still "likely to support liquid water on at least part of their surface for a wide range of possible atmospheres". While the term "tidal locking" is usually synonymous with synchronous rotation, some sources employ a more broad definition that encompass both synchronous (1:1) and asynchronous (i.e. 3:2) spin-orbit resonances. The authors of this paper never clarify which definition they're using, but they cite multiple sources that use it as a synonym for synchronous rotation, so that's what I assume they mean.

Source of parallax.

Source of habitable zone boundaries and planets b, c, and d radius. See the orbital plot of the Teegarden's Star system available as an image on the page or via a link to a Google Drive folder. The plot make it clear that all three planets are well within the so-called "tidal lock line".

Source of planets b, c, and d mass, semimajor axis, orbital period, and eccentricity.

This paper concluded that Teegarden's Star is "a generally inactive star, which is nevertheless capable of producing substantial flaring" comparable to "large solar flares." However, because planets b, c, and d have much tighter orbits, they "receive higher X-ray fluxes than the Earth."

According to this paper, planets b and c have a 98.45% and 92.84% probability of hosting a subsurface ocean, respectively.

Source of mass, radius, luminosity, temperature, and metallicity.

An early article about the Wow! Signal written by John Kraus, the designer and director of the Big Ear telescope.

A brief summary of the Wow! Signal written by John Kraus.

A detailed retrospective written by Jerry Ehman on the 20th anniversary of the Wow! Signal.

A brief summary of the Wow! Signal written by SETI Institute astronomer Seth Shostak.

A detailed retrospective written by Jerry Ehman on the 30th anniversary of the Wow! Signal.

A brief retrospective about the Wow! Signal written by Jerry Ehman.

As I was wrapping up this video, the authors of this paper announced that they had revised some of the parameters of the Wow! Signal. Most notably, the signal's duration, frequency, and location. Duration: The Big Ear telescope sampled the intensity of incoming signals every 12 seconds, so the Wow! Signal had a duration of approximately 72 seconds since it was present in six such samples. However, that number is merely an approximation. The authors of this paper found a more precise duration of 73.4 seconds. Frequency: Jerry Ehman estimated in reference #107c above that the Wow! Signal had a frequency of 1420.4556 MHz. The authors of this paper estimate a frequency of 1420.726 MHz. Location: Jerry Ehman estimated in the same reference mentioned above that the two central right ascension values of the two telescope feed horns (regions) in which the Wow! Signal was detected were 19h25m31s and 19h28m22s. The authors of this paper have refined these values ever so slightly to 19h25m02s and 19h27m55s. The authors also re-investigated and ruled out a few commonly proposed solutions to the Wow! Signals such as interference and satellites. See also reference #114 for a complementary paper to this one.

While there's no indication when this article was published visible on the page itself, Robert Kerr was kind enough to send me an early draft of the article which is dated July 25, 2012, so it was definitely written before the transmission commenced.

A promotional video about the Wow! Reply. You can also find various celebrity greetings on this channel if you simply search for "Wow! Reply".

A retrospective article about the Wow! Reply by Ben McGee, one of the presenters of Chasing UFOs.

A page on the website of Campfire, the consulting firm that conceived of the Wow! Reply to promote Chasing UFOs.

After contacting Robert Kerr, he sent me a text file containing all the tweets that the Wow! Reply team planned to transmit into space. Based on the filename (tweets_19228), there were a total of 19 228 tweets (one tweet per line). However, upon opening the file, I found that many of the lines were blank. This was probably due to filtering because tweets deemed inappropriate for one reason or another are known to have been removed. After removing the blank lines, I was left with 17 237 tweets. In the file provided here, I have further removed the date, timestamp, and username ahead of every tweet for the sake of anonymity. The lines are sorted by date in ascending order just like in the original file. The first tweet was posted on June 25, 2012, and the last on June 30, 2012. Presuming the tweets were transmitted in the order in which they appear in this file, then some unknown number of tweets near the top are the only ones that made it into space.

This document (sent to me by Robert Kerr and written by an unknown author) briefly outlines the methodology for converting the tweets into binary and the components of the primer (described as a "training header") prepended to every tweet.

Based on reference #108j above, I did my best to reconstruct the primer prepended to all the Wow! Reply tweets. However, the explanation is a bit vague so this is merely a best guess.

General information about HD 54351.

Source of parallax.

Source of low age estimate.

Source of high age estimate.

Source of mass, radius, and luminosity.

Source of temperature and metallicity.

A few years before Lone Signal, planetary scientist Michael Busch conceived of an encoding scheme for interstellar messages where each number, symbol, word, and concept is represented by an eight-digit string. After writing a message using this rudimentary language, Busch gave it to astrophysicist Rachel Reddick, who was able to decode it with no assistance from Busch. The message was independently decoded by five undergraduates as well. While the encoding scheme presented in this paper is similar to the one that Busch used to write the Lone Signal primer (see reference #115n below) a few years later, they are not the same.

This research paper about METI was funded and written by the team behind Lone Signal. According to the cited pages, they originally planned to use an antenna called "Madley 49" at the Madley Communications Center in England, supposedly equipped with a transmitter that could output 10 kW of power.

This document provides detailed information about Lone Signal and the primer designed by Michael Busch. It also outlines some of the maintenance that the Lone Signal team planned to perform on the Jamesburg Earth Station. For instance, they planned to install a frequency modulator as well as a transmitter capable of 3 kW of output power. However, in personal correspondence with Busch, he told me the Lone Signal team was unable to acquire a frequency modulator before the project was shut down. Instead, they had to use phase modulation, which, according to Busch, is not resilient enough to survive a trip through interstellar space. The document is undated, but the text suggests it was written in late April or early May, 2013.

Some images from an event in New York City celebrating the launch of Lone Signal.

An archived version of the Lone Signal homepage.

While the reporter in this news segment says "30 to 40 000 messages" were transmitted into space "two days a week", this is not correct according to co-founder Pierre Fabre (see reference #115m below).

One of the last updates about Lone Signal posted by co-founder Pierre Fabre on the project's official forum.

Final post on the Lone Signal Tumblr page.

This is a Disqus comment thread that was originally displayed underneath an article about Lone Signal by Gabrielle Pickard on a now defunct website called Top Secret Writers. The cited comment is by Lone Signal co-founder Pierre Fabre, and he states that a total of 8 201 messages were transmitted before the project was abandoned (credit goes to Paul Quast for finding this; see reference #2).

This Google Drive folder contains both the plaintext and encoded versions of the Lone Signal primer. They were created and kindly provided by Michael Busch. Busch told me he created two versions of the primer that he called Test Message 3.0 and 3.1. The 3.0 version was made while Lone Signal was planing to use an antenna at Madley Communications Center in England. The 3.1 version (the one provided here) was made when they switched to using the Jamesburg Earth Station in California.

General information about Gliese 526.

While Gliese 526 is an active flare star, it is noted for having relatively "low activity levels" in this paper.

Source of high age estimate.

Source of parallax.

Source of low age estimate, temperature, and metallicity.

Source of mass, radius, and luminosity.

This is an archived press release on a JAXA website announcing the 2013 transmission. See the PDF linked on the page for more information.

A brief article about the 2013 transmission by Shin-ya Narusawa.

Astronomer Shin-ya Narusawa briefly mentioned the 2013 transmission in this book. It also includes an image of the bitmap that was transmitted. The ebook I purchased has no page numbers so the cited pages (based on page count) could be slightly off from other editions.

This page contains a schedule and some basic information about the 2013 space camp at Usuda.

This and the three references directly below are tweets about the 2013 and 2014 transmissions by Shin-ya Narusawa.