Voyager 1 and 2, Humanity’s Interstellar Envoys, Soldier On at 45

The two probes made flybys of Jupiter and Saturn in the 1970s. Today they’re still doing science way out beyond our solar system.

Today is the 45th anniversary of the launch of Voyager 1, one of humanity’s iconic twin emissaries to the cosmos. (Its sibling, Voyager 2, launched a couple of weeks earlier.) Now in the dark, far reaches of interstellar space—more than 10 billion miles from home, where our sun looks like any other bright star—the pair are still doing science. They carry with them the Golden Records, bearing the sounds and symbols of Earth, should some extraterrestrial ever rendezvous with one of the spacecraft and become curious about its distant sender.

“I’ve been following the arc of Voyager over my career,” says Linda Spilker, Voyager’s deputy project scientist at NASA’s Jet Propulsion Laboratory, who started at the agency in 1977, the year the probes launched. “I’m amazed at how long both of these spacecraft, Voyager 1 and Voyager 2, have been able to keep going and return unique science about new places that no spacecraft has visited before. And now they’ve become interstellar travelers. How cool is that?”

The two car-sized probes, each with a 12-foot antenna mounted on top, had one primary task: to visit the gas giants in our own solar system. After their launches, the Voyagers’ paths diverged, but they both took advantage of a rare planetary lineup, snapping groundbreaking photos as they flew by Jupiter, Saturn, Uranus, and Neptune and revealed tantalizing details about the planets’ moons. By the end of 1989, they’d completed that mission. In 1990, Voyager 1 capped it by turning around and taking a poignant image of our own world, which astronomer and science communicator Carl Sagan dubbed the Pale Blue Dot.  

“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, has lived out their lives,” Sagan wrote. The image of the Earth from a cosmic perspective—a mere “mote of dust suspended in a moonbeam,” as he put it—became nearly as memorable as the Earthrise photo taken by an Apollo 8 astronaut showing the planet as seen from the moon.

The two probes, which run on nuclear-powered systems called radioisotope thermoelectric generators (RTGs), kept flying. Our solar system has no clear boundary, but in the 2000s they crossed the “termination shock,” where solar wind particles abruptly slow below the speed of sound due to pressure from the gas and magnetic fields in interstellar space. Then in the 2010s, they breached the heliopause, the boundary between the solar wind and the interstellar wind. 

With four instruments operating on Voyager 1 and five aboard Voyager 2, they now have a new job: measuring the magnetic field strength, the density of the plasma, and the energy and direction of charged particles in the environment they’re traveling through. “The purpose of the interstellar mission is to measure the sun’s effects as we go further and further from Earth. We’re trying to find out how the sun’s heliosphere interacts with interstellar space,” says Suzanne Dodd, project manager of the Voyager interstellar mission at JPL. Voyager 1 is currently 14.6 billion miles from home, and Voyager 2 is 12.1 billion miles away, but for perspective, the nearest star is some 25 trillion miles away. (NASA maintains a tracker of their journeys.) It’s a remarkable coda for their mission, decades after the probes completed their main goals. 

But they’ve always had a secondary task: conveying a message to any aliens from beyond the solar system who might one day peek inside a craft. Each one carries a Golden Record, which looks like vinyl but is made of metal. A team of scientists and artists, including Sagan and Frank Drake, who died last Friday, packed music, nature sounds, messages, photos, and more on each record—and they included players and instructions, should anyone find them. The ambitious project seeks to tell a story about humanity, what humans aspire to, and our world. It includes the music of Bach and Chuck Berry, and images of families, homes, and scientific advances. “The purpose of the record was to try to answer questions that we would have,” says Jon Lomberg, a scientific artist and the designer for the Golden Records team. “What were the beings like who sent it? What do they look like? What do they act like? What was their world like? So it’s really a self-portrait.”

Unlike the search for extraterrestrial intelligence, or SETI, the records are not designed to be a prelude to first contact. In fact, the Golden Records might be found millions of years from now, perhaps when human civilizations no longer exist. “It’s more like finding a fossil,” says Lomberg. “You can’t talk to the dinosaurs. This is a relic—our obituary in a way, the memento that we were once here.”

The Voyager probes were preceded by the Pioneer missions, which carried small metal plaques with symbolic messages. (The pair of Pioneers left the solar system in the 1980s and ’90s, but they’re no longer functioning.) But no space mission since has incorporated a similar record of humanity—though NASA’s New Horizons, for example, which flew by Pluto in 2015, offered another chance. That was a missed opportunity, Lomberg says, although it might still be possible to send a digital message to the spacecraft’s computer. That would be durable, but it would not last as long as the Golden Records.

The Voyagers have had a tangible influence on space exploration ever since. Their success inspired NASA and other agencies to revisit the outer planets, especially Jupiter and Saturn, and their myriad moons. These subsequent missions include Galileo, Juno, Cassini, and the European Space Agency’s Huygens lander, plus new probes in the works, such as the Europa Clipper, Dragonfly, ESA’s JUICE, and potential voyages to Uranus and Saturn’s moon Enceladus.

The Voyagers influenced pop culture too. The first Star Trek movie in 1979 included an alien spacecraft called “V’ger,” which was actually an altered fictional “Voyager 6.” Voyager and the Golden Records have turned up in TV shows like Saturday Night Live, The West Wing, and—of course—The X-Files. The composer Dario Marianelli even wrote a Voyager-inspired violin concerto.

The pair of spacecraft have lasted far longer than anyone imagined—and, Dodd says, the instruments are working and the data is still great. But they’re showing signs of age. In May, she and her team encountered a glitch in Voyager 1’s telemetry data, which would normally provide information to scientists back home about what the probe’s instruments are doing and whether they’re working properly. The data had been coming back garbled. Addressing the issue was complicated by the vast distance involved, since messages to and from Voyager 1 now take nearly 22 hours. 

Then last week, the team figured out what was wrong. Apparently, the attitude control system had suddenly started sending the telemetry data through the wrong computer, which was no longer working properly. They resolved the problem by routing the data back to the correct computer. “The spacecraft is healthy, it’s happy. It’s returning science data just beautifully,” Spilker says.

Even if Dodd, Spilker, and their colleagues can keep resolving these kinds of technical issues, however, the spacecraft have a more enduring problem: their power supplies. Their RTG systems provide power by converting heat from the radioactive decay of plutonium-238 into electricity. But after 45 years, the fuel is now generating 4 watts less per year. Dodd and her team have turned off any systems and instruments not involved in the interstellar mission—and in 2019, they started turning off heaters in some of the instruments that are still running. That added a couple of years to the spacecrafts’ lifespans.

Nevertheless, the Voyager probes might only have a few years, or perhaps a decade, left in them. Eventually, their dwindling power won’t be sufficient to run their instruments. “At that point, the Voyagers will become our silent ambassadors,” Spilker says.

As they hurtle at 35,000 miles per hour into the unknown with their powered-down machines, they will still carry humanity’s message in a bottle. “The Golden Record, a piece of human civilization, a piece of technology with a 1970s stamp on it—that is going to persevere. It’s not degrading. It’s going to last for billions of years. It’s going to outlast the planet that it came from. That’s mind-blowing kind of stuff,” says Jim Bell, a planetary scientist at Arizona State University and the author of a book on the Voyager mission’s 40th anniversary.

Bell speculates that it might not be aliens, but our own descendants, who ultimately spot the far-flung spacecraft. “My prediction is that the message really is going to be for us. We’re going to be the ones who go find it—in the far future, when it becomes easy to travel and be tourists and see the Voyagers,” he says. “We’ll be thinking: Wasn’t that one of the most amazing things we did as a species in the 20th century?”

Voyager 1 and 2, Humanity’s Interstellar Envoys, Soldier On at 45

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