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Happy Halloween! This has nothing to do with Halloween.

In 1977, in response to a fortuitous alignment of the outer planets of our solar system, NASA launched space probes Voyager 1 and 2 to tour the outer planets and transmit photographs back to Earth. In that capacity the Voyagers were spectacularly successful, sending tens of thousands of images of planets and moons back to Earth via radio. Both probes passed beyond the orbit of Pluto in the late 1980s, and they continue on toward interstellar space traveling at approximately 37,000 mph (almost 60,000 kph). They continue to transmit data back to Earth, and are expected to do so until around 2025, when their radioisotope thermoelectric generators will be exhausted, and unable to power any instruments.

In 40,000 years or so, Voyager 1 will pass within 1.6 light-years of the star Gliese 445, and at around the same time Voyager 2 will be within 1.7 light-years of the star Ross 248. If either of these systems happen to be home to an advanced alien civilization, there’s a chance they will detect and retrieve one of our plucky nuclear space robots.

In anticipation of the possibility of such proxy contact, NASA mission designers affixed a message from humanity to the side of each probe in the form of a phonograph record. These gold-plated copper records each contain an identical compilation of sounds and music from all over the Earth, as well as analog-encoded images. In the event that one of the probes is ever discovered by an intelligent alien species, the included instructions will hopefully allow them to decode the sounds and sights of our civilization.

We at Damn Interesting have put together an online simulation of what an alien civilization might see and hear upon decoding one of the records, assuming that their seeing and hearing abilities are similar to our own. For the best experience, a laptop or desktop screen size is recommended. We share these sounds and images under the “fair use” exception to copyright law due to the historical significance of the media. You can launch the interactive now, or read on for more background and technical detail.

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Mounting a record to a Voyager probe

The eclectic contents of the golden records were curated by a committee chaired by Dr. Carl Sagan. The records were designed to be played at 16.67 rpm⁠—half the usual speed of a typical phonograph record⁠—trading audio fidelity for extended length. For the approximately two hours of sounds, the committee selected vocal greetings in 55 Earth languages; sounds such as thunder and machinery; and music from around the world. Unfortunately, Sagan’s committee failed to credit many of indigenous performers whose music was featured on the record, instead crediting the anthropologists and musicologists who recorded the songs. As much as possible we have attempted to properly credit the artists in our interactive, but there are still some we have been unable to identify. The records also include the song of the humpback whale, and an hour’s worth of brainwaves recorded from Sagan’s fiancée Ann Druyan, sped up to condense them into ten seconds of audio.

The images on the record are analog-encoded, each composed of 512 lines. The first image is a “calibration circle,” intended to verify to the decoders that they have succeeded in translating the analog data into an image. Following this are 121 images featuring mathematical definitions; diagrams and photos of our solar system; human anatomy; scenes from Earth; and written messages from humans associated with the project. Some of these photos are in color, using an image of the solar spectrum to provide a 12-bit color key, permitting a total of 4,096 colors.

Each record is enclosed in a protective, gold-plated aluminum jacket, together with a cartridge and a needle. Symbols etched into the protective cover attempt to convey where the spacecraft came from, and and how to decode the contents of the record. This cover also contains an ultra-pure source of Uranium-238 that an alien civilization could use as a radioactive clock to deduce the age of the craft, by measuring the remaining Uranium-238 and calculating based on its half-life.

Sagan and his team chronicled the effort to design the golden records in the 1978 book Murmurs of Earth. A later edition included two CD-ROM discs reproducing the contents of the golden records. Unfortunately the book and CDs have been out of print for years.

A Voyager photograph of Jupiter

Given the vast, huge, mind-boggling bigness of outer space, it is unlikely that any alien civilization will ever discover our small, cold probes floating past their stellar neighborhoods, nor our gilded greetings thereon. But on a long timeline, in a large universe, “unlikely” isn’t as hopeless as it might sound. Furthermore, having made the effort to send the message is in some ways its own reward. As Dr. Sagan himself observed:

“The spacecraft will be encountered and the record played only if there are advanced spacefaring civilizations in interstellar space. But the launching of this bottle into the cosmic ocean says something very hopeful about life on this planet.”

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