Facebook
Twitter
Pocket
Reddit
Email
When the two Voyager probes launched into space in 1977, they were headed to uncharted territory. It was the first time humanity had sent robot spacecraft to study up close the four giant outer planets of our solar system: Jupiter, Saturn, Uranus, and Neptune. Stunning images and scientific data captured by the probes over the next few decades altered our understanding of the cosmos.
Through the Voyagers, we learned of Jupiter’s turbulent atmosphere, the tilted magnetic field of Uranus, a rotating storm on Neptune called the Great Dark Spot, and Saturn’s dynamic rings. We also discovered 23 new moons of the outer planets and found that these moons were not the dead, frozen worlds scientists had suspected. Saturn’s moons appeared to be composed mostly of water ice, while active volcanoes on Jupiter’s moon Io spewed lava dozens of miles high. Eventually, the two spacecraft would explore not just the four giant planets, but 48 of their moons, as well as the rings, atmospheres, and magnetic fields those planets possess.
Once the Voyagers’ tour of the four planets was complete in 1990, the world’s attention faded; but the probes continued to provide remarkable insights into the dynamics of the solar system, including ultraviolet sources among the stars and the boundary between the sun’s influence and interstellar space. Even today, both probes continue sending back data about the interstellar medium, the space between the stars, says Linda Spilker, NASA’s project scientist for the Voyager missions—including precise measurements of the density and temperature of the thin ionized gases it contains and the incidence of high-energy cosmic rays.
Some experts give the Voyagers only about five years before we lose contact.
More than 45 years after they first launched, the Voyagers are now NASA’s longest-lived mission and the most distant human-made objects from the Earth—but they will one day soon go offline and drift silently into the final frontier, perhaps for eternity. NASA has been progressively shutting down the instruments and cameras on the spacecraft for decades, to extend their working lives to the limit by using as little electricity as possible. One of Voyager 1’s last photographs, for example, was the famous “Pale Blue Dot” taken in 1990, shortly before its cameras were powered off forever. And since the late 1990s, engineers have commanded both Voyagers to shut down instruments related to plasma science, the strength of electromagnetic fields, and the analysis of starlight.
Some experts give the Voyagers only about five years before we lose contact. “There’s been a big push to try to keep the mission going until the 50th anniversary of their launches,” in 2027, says Johns Hopkins space scientist Ralph McNutt, who witnessed the Voyager 1 launch from Florida’s Cape Canaveral in 1977 and has been involved with the Voyager missions throughout his career. “We’ll see.”
According to NASA, Voyager 1 is now more than 15 billion miles from Earth, about three times the average orbit of Pluto, where radio signals take about 23 hours to reach it; while its twin Voyager 2 is almost 13 billion miles away. The probes are still in fragile radio contact with Earth, and their instruments show both have passed the “heliopause”—the theoretical outer edge of the solar system, where the wind of charged particles from the sun finally comes to an end. They are now drifting through interstellar space.
But the probes are running critically short of electricity from what are called their “nuclear batteries”—actually radioisotope thermoelectric generators that make electricity from the radioactive decay of plutonium. The fading power of the probes and the difficulties of making contact over more than 10 billion miles means that, one day soon, one or other of the Voyagers won’t answer NASA’s daily attempts to communicate via the Deep Space Network of radio dishes. Both probes use heaters to keep key instruments warm and keep the hydrazine in the fuel lines liquid: When the fuel freezes up, the probes won’t be able to use their thrusters to keep their main radio antennae pointed at the Earth, and their communications will come to an end.
Newer space probes are now exploring the outer reaches of the solar system, including the New Horizons mission to Pluto. McNutt is overseeing an instrument on that probe, which is now heading for the “termination shock” where the solar wind first impacts the interstellar medium, about 5.5 billion miles from the Earth—almost twice the distance from Earth to Pluto. He’s also one of the principal scientists behind the Interstellar Probe proposal, which could launch as soon as 2036. Its technology will be 50 years more advanced than the Voyagers, and it could reach the same distance in half the time.
For McNutt, it’s a “pleasant surprise” that the Voyagers are still working after all these years: “I joke with people: If you go back and look at the original papers, the Voyagers were designed to work for four and a half years,” he says. “We’ve outlived the warranty by a factor of 10.”
Even when the Voyagers can no longer communicate with Earth, it will not be the end of their mission. Both probes bear the famous 12-inch “golden record” of the sounds of Earth, greetings in more than 50 languages, music by Mozart and Chuck Berry, and a star map showing how to get here. The designers of the probe hoped that one day these records might be played by alien spacefarers far from Earth.
And their hopes may someday come true: Voyager 1 will get relatively near a star in the constellation Camelopardalis in about 40,000 years, while Voyager 2 will near a star in the constellation Andromeda at about the same time. It’s possible that the Voyagers may one day be overtaken by newer probes from Earth, but for now they are humanity’s ambassadors to the stars; when their communications to the Earth cease, that will become their final mission. 
Lead image: Dotted Yeti / Shutterstock
Get the Nautilus newsletter
Cutting-edge science, unraveled by the very brightest living thinkers.
