Voyager 1 and 2
Voyager 1 and Voyager 2 are NASA's two most distant working spacecraft, launched within weeks of each other in 1977. Originally meant to do a four-year tour of the outer planets, both probes are still operating almost 50 years later, sending faint signals back from beyond the edge of the Solar System. Voyager 1 is now in interstellar space, the first human-made object to leave the protective bubble of the Sun. Each carries a Golden Record: a message from humanity to anyone (or anything) that might find it in the far future.
- LaunchedAugust/September 1977Two weeks apart
- Distance Voyager 1approx. 24 billion kmFurthest man-made object
- Distance Voyager 2approx. 20 billion kmGoing in a different direction
- Speed Voyager 1approx. 17 km/sRelative to the Sun
- Planets visitedJupiter, Saturn, Uranus, NeptuneVoyager 2 saw all 4; Voyager 1 only the first 2
- Time for signal to reach Earthapprox. 22 hoursOne way, from Voyager 1
The Grand Tour
In the early 1970s, NASA noticed that the four outer planets (Jupiter, Saturn, Uranus and Neptune) were lining up in a way that happens only once every 175 years. With careful timing, a single spacecraft could use the gravity of each planet to swing on to the next one (a technique called gravity assist), allowing one mission to visit all four giants. NASA approved two probes for this Grand Tour: Voyager 1 (launched 5 September 1977) and Voyager 2 (launched 20 August 1977, two weeks earlier despite the higher number).
Voyager 1: Jupiter and Saturn
Voyager 1 reached Jupiter in March 1979. Its photos revolutionised our knowledge of the planet, showing storms in the Great Red Spot in detail, discovering thin rings of dust around Jupiter, and capturing the first close-up images of Jupiter's four largest moons. The probe found active volcanoes on Io (the most volcanically active body in the Solar System) and hinted at a possible underground ocean on Europa.
Voyager 1 reached Saturn in November 1980. It studied Saturn's rings in unprecedented detail, found new moons, and made a close pass of the huge moon Titan to study its thick atmosphere. Studying Titan was important enough that Voyager 1 sacrificed its onward trip; the gravity assist needed to fly close past Titan threw the probe out of the plane of the Solar System, ending any chance of reaching Uranus or Neptune. From there, Voyager 1 headed straight outwards into interstellar space.
Voyager 2: the full Grand Tour
Voyager 2 also visited Jupiter (July 1979) and Saturn (August 1981), but unlike Voyager 1 it kept going to the outer two giants. It reached Uranus in January 1986: the first (and so far only) spacecraft ever to visit Uranus, finding 10 new moons and 2 new rings, and discovering that the planet's magnetic field is wildly tilted compared to its rotation axis.
Three and a half years later, in August 1989, Voyager 2 reached Neptune. It revealed huge storms in Neptune's atmosphere, including a Great Dark Spot the size of Earth, found ring arcs and discovered six new moons. Voyager 2's pass over Neptune's big moon Triton revealed an icy world with active geysers spewing nitrogen into space, one of the few geologically active bodies in the outer Solar System.
After Neptune, Voyager 2 also headed out of the Solar System, just in a different direction from its twin.
Into interstellar space
The Solar System ends not at the orbit of Neptune but much further out, where the solar wind (the stream of charged particles flowing out from the Sun) finally fades into the wider gas of the Milky Way. The boundary is called the heliopause.
Voyager 1 crossed the heliopause in August 2012, becoming the first human-made object to enter interstellar space. Voyager 2 followed in November 2018. Both probes are now travelling through the gas between the stars and still phoning home, with their faint signals taking about 22 hours to reach Earth (one way) from Voyager 1.
The Golden Record
Each Voyager probe carries a 12-inch gold-plated copper phonograph record, fixed to the side of the spacecraft. The Golden Record contains a message to anyone (or anything) that might find it in the future: 115 images of Earth and humans, greetings in 55 languages (including "Hello from the children of planet Earth!"), sounds of Earth (waves, wind, animals, a kiss), and 90 minutes of music from across our species, including Bach, Beethoven, Chuck Berry, classical Indian raga and Aboriginal songs.
The record was put together by a team led by Carl Sagan. It also includes instructions for how to play it (etched into the metal cover), our home address (a pulsar map showing the position of the Sun in the Milky Way), and a sample of Earth radioactive uranium to allow anyone playing it to work out when it was made. The record is good for several billion years.
The end of the mission
The two Voyagers are running out of power. Their nuclear batteries lose a few watts every year, and NASA has been switching off non-essential systems one by one to extend the mission. By the early 2030s, both spacecraft will probably be unable to transmit any signal back. After that, both will continue drifting through interstellar space for billions of years, eventually passing within a few light years of various distant stars in the next 40,000 years.
The two Voyagers may be the longest-lasting things humans have ever made. Long after the Earth is gone, the Voyagers should still be drifting silently between the stars, carrying their Golden Records into the deep future.
Deeper dive: the Pale Blue Dot
On 14 February 1990, with Voyager 1 about 6 billion km from the Sun and on its way out of the Solar System, NASA pointed the probe back towards Earth and took a series of 60 photographs of all the planets. Most of them showed each planet as no more than a few pixels of light. The Earth photo, in particular, showed our entire planet as a single faint blue dot less than a pixel wide, almost lost in a beam of scattered sunlight that happened to hit Voyager's camera at the right angle.
The image was the idea of Carl Sagan, the famous astronomer and science communicator. Sagan thought such a photograph would force humanity to think about its place in the universe. In his 1994 book Pale Blue Dot, he wrote: "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, lived out their lives... Our posturings, our imagined self-importance, the delusion that we have some privileged position in the universe, are challenged by this point of pale light."
The Pale Blue Dot is one of the most reproduced images in the history of science. Voyager 1 took it nearly 35 years ago. Today the probe is more than four times further away, but still trying to send signals home. The photo remains a reminder that our entire world, all of human history, all of human conflict and love and art and science, fits inside a single faint dot of light from far enough away.
For other deep space missions, see Hubble and JWST. For Mars exploration see Mars rovers.