The Current's audience just picked 893 essential songs released since 2000. That resulted in a 61-hour playlist, and based on social media, everyone found plenty of room for debate. Okay, now let's make it really hard.

You have 105 minutes to represent all of human history. Music, speech, sounds...everything. Once you include a message from the U.N. Secretary-General, greetings in 55 languages, a sound collage, an international selection of folk music, a jazz number, and several pieces of classical music, that leaves room for exactly one song from the remaining popular music canon. One single song. It's 1977, so that makes your job a little easier; you can ignore the last four decades of rock, pop, and rap. Okay, one song. Go.

If it were up to the listeners of The Current, it would be Queen's "Bohemian Rhapsody," voted the single most essential song released prior to 1977. If it were up to Carl Sagan, it would be something by Bob Dylan. The latter is more relevant, since it was Sagan who led the team selecting the contents of Voyager's Golden Record — the literal gold-plated record album sent into the stars in an edition of two.

One copy of the record was attached to each of the Voyager space probes launched in 1977. Voyager 1 swung by Jupiter, Saturn, and Saturn's moon Titan, and it's now on its way to a star in the Ursa Minor constellation, where it will arrive in about 40,000 years. Voyager 2 passed Jupiter, Saturn, Uranus, and Neptune; its next stop is a star in the Andromeda constellation.

For the rest of the lifetimes of anyone currently reading this, the Voyager Golden Records will almost certainly be the most distantly distributed musical recordings. In addition to Azerbaijan bagpipes and an aria from The Magic Flute, each record also contains 115 images encoded into soundwaves.

The album cover, taking the frequency of a hydrogen atom's energy emission as a universal frame of reference, explains how to play the record (a cartridge and needle are helpfully included) and decode the images. As various space fans have demonstrated, it's entirely possible to use the instructions to program a computer to decode images illustrating human anatomy (NASA censored a nude couple), nature scenes, and various functions of civilization.

Though not yet the household name he'd become with the 1980 PBS series Cosmos (which drew on data returned by the Voyager craft), Carl Sagan was already America's preeminent celebrity astronomer. The Golden Record project was conceived as a sort of sequel to the Pioneer plaque, a purely visual record sent on earlier space probes. Sagan was on the team that designed that plaque, so naturally he got the call for Voyager. Frank Drake, an astronomer who also worked on Pioneer, hit on the idea of a record. To program its contents, Sagan assembled a team that also included former Rolling Stone science writer Tim Ferris (sample column title: "How Do We Know Where We Are If We've Never Been Anywhere Else?") and Ferris's fiancée, the writer Ann Druyan.

Here's where the rock and roll comes in. Jonathan Scott, author of a new history of the Voyager Golden Record called The Vinyl Frontier, is a music writer who's edited books on Prince and Cher. His description of the music selection process alone is worth the book's price, but it was clear from the beginning that music couldn't be the only audio on the record.

As Scott chronicles, Sagan thought to approach the United Nations, a process that turned predictably political. In the end, he did record a sample of greetings from various delegates, which were mixed with whale song (yes, really) for maximum species inclusiveness. Students and scholars from the language programs at Cornell, where Sagan taught, recorded a multilingual assortment of greetings; that segment of the record ends with Sagan's own six-year-old son saying, "Hello from the children of planet Earth."

Druyan helped curate a collage of Earth sounds including her own brain waves, electronic sounds derived from planetary orbits, various animals, a baby being comforted by its mother, and a human laugh (likely Sagan's). President Jimmy Carter was invited to record a message, but embarrassed by his southern accent, he chose instead to have a written greeting encoded as an image. A list of sitting members of Congress was also included, for purposes of interstellar oversight.

Then, the music. A cranky Alan Lomax was tapped to help Druyan assemble a range of international folk music, and bluesman Blind Willie Johnson's near-instrumental "Dark Was the Night, Cold Was the Ground" also made the cut, as did Louis Armstrong's rendition of "Melancholy Blues." Sagan and team member Jon Lomberg were both fans of classical music, which meant that a generous amount of it would end up on the record.

Despite his accessible mien, Sagan favored the weightiest composers. How weighty? When Lomberg suggested some music by Mozart, he remembers, Sagan replied, "It's kind of lightweight, isn't it?" Lomberg (and Druyan) prevailed, and Mozart made the record — along with Beethoven, Bach, and Stravinsky. While German composers predominated (to the chagrin of Italians), Wagner was ruled out due to his association with anti-Semitism.

That left rock and roll. What was the one pure example of rock music to include on this record sent to the stars? Sagan suggested Dylan, or maybe the Beatles. The Golden Record team went so far as to approach the Beatles (then all still living) about "Here Comes the Sun"; they were reportedly amenable, but their publisher Northern Songs said it would cost $50,000 per copy, totaling $100,000, to license the song. That was prohibitive, so the Beatles were out.

Amusingly, as Scott notes, there was also some concern about the song potentially being taken literally. "We're not sending you the sun," explained Ferris, "we're sending you this record." What if it was taken as a threat?

Other artists were thrown around: Elvis Presley, Bob Marley, Billie Holiday, Jimi Hendrix, Aretha Franklin, Miles Davis, the Rolling Stones. Desperate to be included, Jefferson Starship offered their music for free. (Although the Beatles weren't shot into space, a track recorded at Abbey Road Studios was: a British folk song called "The Fairie Round.")

In a you-can't-make-these-things-up moment, Sagan actually posed the musical million dollar question to one of his classes at Cornell. Among the students was Bill Nye, the future Science Guy, who argued in favor of the song that was ultimately selected.

In the end, Druyan's argument won the day. "It had to be Chuck Berry," she said. "He was the progenitor, you know that crossover between African, European, and American music. And those guitar riffs and those lyrics that went like the lyrics of a novel...I mean, Chuck Berry wrote novels that you could experience in under three minutes."

So "Johnny B. Goode" it was. Druyan won Sagan's heart, too: two days after the launch of Voyager 2, at a moment as carefully coordinated as a rocket launch, both told their respective partners they were ending their current relationships to marry one another.

You can listen to the whole record online, as well as in a deluxe reissue that finally put the record on actual vinyl — despite the book's title, the real records were made of gold-plated copper.

Perfection was never a possibility, but history has generally looked kindly on the decisions the Golden Record programmers made. After all, as Scott notes, when the Golden Record team sat down for one of their key discussions about what music to include,

"When I Need You" by Leo Sayer had just replaced the Eagles' "Hotel California" at the top of the Billboard Hot 100. Annie Hall was doing well at the flicks. The world was about a week away from the premiere of the first Star Wars film. And the 7" of "God Save the Queen" by the Sex Pistols would go on sale in 13 days.

"Think about how bad this record could have been."