As much of the space community’s attention remains focused on the delayed Artemis rocket launch and the return to the moon, two relics of the Space Age continue to make their way across the void between the stars, sending back valuable information to scientists on Earth.
The Voyager 1 and Voyager 2 space probes launched 45 years ago, the first on Aug. 20, 1977 and the second on Sept. 5, and they are now the farthest human-made objects from Earth, at about three times the distance of Pluto from the Sun.
Measurements indicate both probes left the interstellar bubble of our solar system a few years ago. But they’re getting old, and so engineers have been progressively shutting down their systems in the hope that their fading batteries can provide enough power for just a few more years. After that, the probes will shut down completely, and could coast through space forever.
“The two Voyagers have become our first interstellar travelers, sending back information about a place that we’ve never visited before,” said Linda Spilker, NASA’s deputy project scientist on the Voyager missions at the Jet Propulsion Laboratory in Pasadena, California.
It now takes about 22 hours for radio signals from Earth to cover the more than 15 billion miles to Voyager 1, the farthest probe, and another 22 hours to receive its reply. Spilker, who’s worked on the probes since the first launch in 1977, said that keeping contact with them has been a monumental effort using the largest radio telescopes of the Deep Space Network, which NASA uses to relay commands to its spacecraft.
The Voyagers were a big deal when they launched at the height of the Space Age. Their main purpose was to make the first explorations of the solar system’s gas giants and their moons — Jupiter and Saturn by both Voyager 1 and Voyager 2 in 1979 and 1981, and Uranus and Neptune by Voyager 2 in 1986 and 1989, respectively.
The high-resolution color photographs they took and the data they recorded are still crucial to scientific studies today. Their final photo was the Pale Blue Dot, a portrait of the solar system taken by Voyager 1 in 1990, at about 6 billion miles away from Earth.
After their dramatic planetary fly-bys, however, the Voyager probes began a quieter phase of their journey, heading for the very edges of our solar system and beyond. Onboard instruments that measure charged particles in space indicate Voyager 1 left the protective bubble of particles emitted by the sun in 2012, while Voyager 2 left it in 2018. That means that both probes are now technically in interstellar space — between stars — and yet they are still sending back vital data from their onboard instruments, Spilker said.
Where the Voyager probes have led, others will follow. A panel to set the nation’s scientific priorities for the next 10 years is considering a proposal for a $3.1 billion Interstellar Probe (IP) that could reach the Voyagers’ current location in as little as 15 years. If it’s approved in 2024, the probe could be launched by 2036.
Ralph McNutt, who heads space science at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, has worked on the Voyager missions for his entire career. He witnessed the Voyager 1 launch in September 1977, and he’s now a leader of the IP project.
“We can get to a speed of about twice that of Voyager 1, and get about twice as far before the Interstellar Probe runs out of power,” he said.
The newer probe would be much more capable than the Voyagers, which were built with 45-year-old technology, and the project’s planners now have a much better idea of what’s possible and what to expect on the journey.
The key transmitter on the new probe and its instruments, including magnetometers and spectrometers, would be many times more powerful than their 1977 equivalents. And the IP could also visit some of the mysterious Kuiper Belt objects in the outer reaches of the solar system, which are thought to be the origins of some comets, McNutt said.
Until the Interstellar Probe gets the green light, however, the Voyagers will be humanity’s foremost representatives in interstellar space. In about 40,000 years, Voyager 1 will get relatively close to another star in the constellation Camelopardalis, while Voyager 2 will near a star in the constellation of Andromeda on its way to the giant star Sirius, which it will reach in roughly 300,000 years.
Long before then, however — in as little as 10 years — both Voyager probes will completely run out of power, Spilker said. Each probe is powered by plutonium batteries, but they’ve already started to weaken, and every few months NASA engineers order the probes to shut down a few more of their onboard systems. Their hope is that they can eke enough power out of the batteries so some of the instruments can keep working, at least until the 50th anniversary of the twin launches in 2027.
After that, who knows?
“Fingers crossed, if everything goes as planned, we could get to the 2030s,” she said.
Whenever their power does finally run out, the Voyager probes will serve as “silent ambassadors” to the stars, Spilker said. Each probe is carrying a record, imprinted on gold, of sounds on Earth, including a baby’s cry, a whale’s song, music by Mozart and Chuck Berry, and greetings in 55 different languages.
“Maybe some other civilization will find them, and will want to know more about the Earth,” Spilker said.