NASA's Voyager Missions Are Equipped With Maps That Could Lead Extraterrestrial Life to Earth

The 40th anniversary of the launch of two of NASA's most remarkable spacecraft is fast approaching.

The Voyager 2 mission launched into space on August 20, 1977, followed by Voyager 1 on September 5, 1977. And since their departure from Earth, both spacecraft have accumulated various accolades.

Voyager 1 is the first spacecraft to enter interstellar space—the region outside the heliosphere, a giant electromagnetic bubble created by the sun—and is the most distant human-made object ever. And Voyager 2 is the only spacecraft to fly by all four planets of the outer solar system: Jupiter, Saturn, Uranus and Neptune.

But the lasting legacy of the missions may be yet to come. Ahead of the anniversary, the daughter of a key figure in the missions has recalled a treasure that was sent on board the spacecraft: a map designed to guide any forms of intelligent extraterrestrial life they encountered back to Earth.

Frank Drake, a prominent astronomer, was one of two people who designed a map that uses pulsars—a type of neutron star, the collapsed core of a dying star—to locate the solar system in a way intelligible to life forms outside it. Copies of the map are etched into both of the Voyager spacecraft.

Drake said the map was designed to be potentially intelligible to any potential forms of alien life. "We needed to put something on the Voyager that said where it came from and how long it was traveling," Drake told his daughter, Nadia Drake, in a piece for National Geographic.

The map is stamped onto the cover of the Voyager Golden Record, a phonograph record that contains a series of sounds, images and music that are supposed to represent the diversity of life on Earth. It shows the location of the solar system relative to 14 pulsars, with the length of lines connecting the pulsars to a central point—symbolizing the sun—representing how far away they are from Earth.

Pulsars appear from Earth as blinking celestial objects. These stars, first discovered in 1967 and still not well understood by astrophysicists, emit two beams of light in opposite directions and constantly spin, giving the impression of a flickering light.

Different pulsars spin at different rates, the slowest at one spin per second, the fastest at more than 700 times per second. The rate at which the light they emit appears to blink can be used to determine the rate at which the pulsar is spinning. The spin rate of a pulsar slows down as it ages.

Drake said that he chose to use pulsars as reference points for the map because they remain active for up to billions of years. Also inscribed on the map, in binary code, was the pulsar's spin rate at the time the map was drawn in 1971. Should an intelligent being find the map, it could theoretically calculate the difference between the pulsar's spin rate at the time the map was found and the spin rate inscribed on the map, thereby determining exactly when the map was made.

"There was a magic about pulsars.... No other things in the sky had such labels on them," he said.

Nadia Drake has previously shared an image of the draft version of the pulsar map:

Frank Drake has been a prominent figure in the search for extraterrestrial life. He was on the original board of trustees of the SETI Institute (an acronym for search for extraterrestrial intelligence) and also wrote the Arecibo message, an interstellar radio message containing basic information regarding humanity and Earth. The message was broadcast into a spherical cluster of stars, known as Messier 13, in the hope that some form of intelligent life would receive it.

But others have been more skeptical about whether humans should be so forthright in reaching out to possible extraterrestrial life forms. Among them are Stephen Hawking, the University of Cambridge physicist, who has said that humans should listen for signals from aliens rather than broadcasting our own. Hawking has raised concerns that any forms of alien life may be "vastly more powerful [than humans] and may not see us as any more valuable than we see bacteria."

The Voyager missions have now been exploring space for almost 40 years; both are expected to run until around 2025, by which time Voyager 2 should have joined its companion in interstellar space. But should the spacecraft ever be found by distant intelligent life, they could cement their reputation as NASA's most important missions ever.