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Voyager 1: Earth's farthest spacecraft

An artist's illustration of NASA's Voyager 1 spacecraft, the farthest human-built object from Earth, which launched in 1977 and reached interstellar space in 2012.
An artist's illustration of NASA's Voyager 1 spacecraft, the farthest human-built object from Earth, which launched in 1977 and reached interstellar space in 2012. (Image credit: NASA)

Voyager 1 is the first spacecraft to reach interstellar space. It originally launched (along with its twin, Voyager 2) in 1977 to explore the outer planets in our solar system. However, it has remained operational long past expectations and continues to send information about its journeys back to Earth. 

The spacecraft entered interstellar space in August 2012, almost 35 years after its voyage began. The discovery wasn't made official until 2013, however, when scientists had time to review the data sent back from Voyager 1.

Voyager 1 was actually the second of the twin spacecraft to launch, but it was the first to race by Jupiter and Saturn. The images Voyager 1 sent back have been used in schoolbooks and by many media outlets for a generation. The spacecraft also carries a special record that's designed to take voices and music from Earth out into the cosmos. 

Voyager 2 launched on Aug. 20, 1977, and Voyager 1 launched about two weeks later, on Sept. 5. Since then, the two spacecraft have been traveling along different flight paths and at different speeds. The Voyager missions took advantage of a special alignment of the outer planets that happens just once every 176 years. This alignment allows spacecraft to gravitationally "slingshot" from one planet to the next, making the most efficient use of their limited fuel.

Voyager 1's next big encounter will take place in 40,000 years, when the probe comes within 1.7 light-years of the star AC +79 3888. (The star is roughly 17.5 light-years from Earth.) However, Voyager 1's falling power supply means it will probably stop collecting scientific data around 2025.

Voyager at 40: 40 photos from NASA's epic 'Grand Tour' mission

Voyager 1 facts at a glance

— Voyager 1's body is about the size of a subcompact car, though the boom for its magnetometer instrument extends 42.7 feet (13 meters).
— At launch, the probe weighed 1,797 pounds (815 kilograms). Its mass has decreased a bit over time as the probe has burned its fuel.
— It launched on Sept. 5, 1977, to study the Jupiter and Saturn systems in depth. Voyager 1 flew by Jupiter on March 5, 1979 and cruised past Saturn on Nov. 12, 1980.
— Voyager 1 entered interstellar space on Aug. 25, 2012, becoming the first human-made object ever to do so.
— As of January 2022, Voyager 1 is about 14.5 billion miles (23.3 billion kilometers) from Earth. That's roughly 156 times the distance from our planet to the sun. 

The Grand Tour

NASA originally planned to send two spacecraft past Jupiter, Saturn and Pluto and two other probes past Jupiter, Uranus and Neptune. Budgetary reasons forced the agency to scale back its plans, but NASA still got a lot out of the two Voyagers it launched.

Voyager 2 flew past Jupiter, Saturn, Uranus and Neptune, while Voyager 1 focused on Jupiter and Saturn.

NASA's twin Voyager spacecraft launched in August and September 1977. Aboard each spacecraft is a golden record, a collection of sights, sounds and greetings from Earth. There are 117 images and greetings in 54 languages on each record, with a variety of natural and human-made sounds like storms, volcanoes, rocket launches, airplanes and animals. (Image credit: NASA)

Recognizing that the Voyagers would eventually fly all the way to interstellar space, NASA authorized the production of two Golden Records to be placed on board the spacecraft. Sounds ranging from whale calls to the music of Chuck Berry were placed on board, as well as spoken greetings in 55 languages.

The 12-inch-wide (30 centimeters), gold-plated copper disks also included pictorials showing how to operate them and the position of the sun among nearby pulsars (a type of fast-spinning stellar corpse known as a neutron star), in case extraterrestrials someday stumbled onto the spacecraft and wondered where they came from.

Both spacecraft are powered by three radioisotope thermoelectric generators, devices that convert the heat released by the radioactive decay of plutonium to electricity. Both probes were outfitted with 10 scientific instruments, including a two-camera imaging system, multiple spectrometers, a magnetometer and gear that detects low-energy charged particles and high-energy cosmic rays. Mission team members have also used the Voyagers' communications system to help them study planets and moons, bringing the total number of scientific investigations on each craft to 11.

Eye on Jupiter

Voyager 1 almost didn't get off the ground at its launch, as its rocket came within 3.5 seconds of running out of fuel on Sept. 5, 1977.

But the probe made it safely to space and raced past its twin after launch, getting beyond the main asteroid belt between Mars and Jupiter before Voyager 2 did. Voyager 1's first pictures of Jupiter beamed back to Earth in April 1978, when the probe was 165 million miles (266 million kilometers) from home.

To NASA's surprise, in March 1979 Voyager 1 spotted a thin ring circling the giant planet. It found two new moons as well — Thebe and Metis. Additionally, Voyager 1 sent back detailed pictures of Jupiter's big Galilean moons (Io, Europa, Ganymede and Callisto) as well as Amalthea.

Like the Pioneer spacecraft before it, Voyager's look at Jupiter's moons revealed them to be active worlds of their own. And Voyager 1 made some intriguing discoveries about these natural satellites. For example, Io's many volcanoes and mottled yellow-brown-orange surface showed that, like planets, moons can have active interiors.

Additionally, Voyager 1 sent back photos of Europa showing a relatively smooth surface broken up by lines, hinting at ice and maybe even an ocean underneath. (Subsequent observations and analyses have revealed that Europa likely harbors a huge subsurface ocean of liquid water, which may even be able to support Earth-like life.)

Voyager 1's closest approach to Jupiter was on March 5, 1979, when it came within 174,000 miles (280,000 km) of the turbulent cloud tops. Then it was time for the probe to aim for Saturn.

Saturn's rings and moons

Scientists only had to wait about a year, until 1980, to get close-up pictures of Saturn. Like Jupiter, the ringed planet turned out to be full of surprises.

One of Voyager 1's targets was the F ring, a thin structure discovered only the year previously by NASA's Pioneer 11 probe. Voyager's higher-resolution camera spotted two new moons, Prometheus and Pandora, whose orbits keep the icy material in the F ring in a defined orbit. It also discovered Atlas and a new ring, the G ring, and took images of several other Saturn moons.

One puzzle for astronomers was Titan, the second-largest moon in the solar system (after Jupiter's Ganymede). Close-up pictures of Titan showed nothing but orange haze, leading to years of speculation about what it was like underneath. It wouldn't be until the mid-2000s that humanity would find out, thanks to photos snapped from beneath the haze by the European Space Agency's Huygens atmospheric probe.

The Saturn encounter marked the end of Voyager 1's primary mission. The focus then shifted to tracking the 1,590-pound (720 kg) craft as it sped toward interstellar space.

Two decades before it notched that milestone, however, Voyager 1 took one of the most iconic photos in spaceflight history. On Feb. 14, 1990, the probe turned back toward Earth and snapped an image of its home planet from 3.7 billion miles (6 billion km) away. The photo shows Earth as a tiny dot suspended in a ray of sunlight. 

Voyager 1 took dozens of other photos that day, capturing five other planets and the sun in a multi-image "solar system family portrait." But the Pale Blue Dot picture stands out, reminding us that Earth is a small outpost of life in an incomprehensibly vast universe.

Entering interstellar space

Voyager 1 left the heliosphere — the giant bubble of charged particles that the sun blows around itself — in August 2012, popping free into interstellar space. The discovery was made public in a study published in the journal Science the following year.

The results came to light after a powerful solar eruption was recorded by Voyager 1's plasma wave instrument between April 9 and May 22, 2013. The eruption caused electrons near Voyager 1 to vibrate. From the oscillations, researchers discovered that Voyager 1's surroundings had a higher density than what is found just inside the heliosphere.

It seems contradictory that electron density is higher in interstellar space than it is in the sun's neighborhood. But researchers explained that, at the edge of the heliosphere, electron density is dramatically low compared with locations near Earth. 

Researchers then backtracked through Voyager 1's data and nailed down the official departure date to Aug. 25, 2012. The date was fixed not only by the electron oscillations but also by the spacecraft's measurements of charged solar particles. 

On that fateful day — which was the same day that Apollo 11 astronaut Neal Armstrong died — the probe saw a 1,000-fold drop in these particles and a 9% increase in galactic cosmic rays that come from outside the solar system. At that point, Voyager 1 was 11.25 billion miles (18.11 billion km) from the sun, or about 121  astronomical units (AU).

One AU is the average Earth-sun distance — about 93 million miles (150 million km).

Voyager 1's interstellar adventures

As of January 2022, Voyager 1 is roughly 156 AU from Earth — approximately 14.5 billion miles (23.3 billion km). You can keep tabs on the probe's current distance on this NASA website (opens in new tab).

Since flying into interstellar space, Voyager 1 has sent back a variety of valuable information about conditions in this zone of the universe. Its discoveries include showing that cosmic radiation out there is very intense, and demonstrating how charged particles from the sun interact with those emitted by other stars, mission project scientist Ed Stone, of the California Institute of Technology in Pasadena, told Space.com in September 2017.

The spacecraft's capabilities continue to astound engineers. In December 2017, for example, NASA announced that Voyager 1 successfully used its backup thrusters to orient itself to "talk" with Earth. These trajectory correction maneuver (TCM) thrusters hadn't been used since November 1980, during Voyager 1's flyby of Saturn. Since then, the spacecraft had primarily used its standard attitude-control thrusters to swing the spacecraft in the right orientation to communicate with Earth. 

As the performance of the attitude-control thrusters began to deteriorate, however, NASA decided to test the TCM thrusters — an idea that could extend Voyager 1's operational life. That test ultimately succeeded. 

"With these thrusters that are still functional after 37 years without use, we will be able to extend the life of the Voyager 1 spacecraft by two to three years," Voyager project manager Suzanne Dodd, of NASA's Jet Propulsion , Laboratory (JPL) in Southern California, said in a statement in December 2017 (opens in new tab).

Mission team members have taken other measures to extend Voyager 1's life as well. For example,  they turned off the spacecraft's cameras shortly after the Pale Blue Dot photo was taken to help conserve Voyager 1's limited power supply. (The cameras wouldn't pick up much in the darkness of deep space anyway.) Over the years, the mission team has turned off five other scientific instruments as well, leaving Voyager 1 with four that are still functioning — the Cosmic Ray Subsystem, the Low-Energy Charged Particles instrument, the Magnetometer and the Plasma Wave Subsystem. (Similar measures have been taken with Voyager 2, which currently has five operational instruments (opens in new tab).)

The Voyager spacecraft each celebrated 40 years in space in 2017, prompting celebrations from NASA and celebrities such as "Star Trek" star William Shatner. In September 2017, Shatner read out a message to the spacecraft originally crafted on Twitter by Oliver Jenkins: "We offer friendship across the stars. You are not alone." JPL engineer Annabel Kennedy then transmitted the message to Voyager 1; it was projected to reach the spacecraft in about 19 hours.

"None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey," Stone said in a NASA statement from August 2017 (opens in new tab). "The most exciting thing they find in the next five years is likely to be something that we didn't know was out there to be discovered."

Additional resources

You can learn much more about both Voyagers' design, scientific instruments and mission goals at JPL's Voyager site (opens in new tab). NASA has lots of an-depth information about the Pale Blue Dot photo, including Carl Sagan's large role in making it happen, here (opens in new tab). And if you're interested in the Golden Record, check out this detailed New Yorker piece (opens in new tab) by Timothy Ferris, who produced the historic artifact.

Bibliography

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Elizabeth Howell
Elizabeth Howell

Elizabeth Howell, Ph.D., is a staff writer in the spaceflight channel since 2022. She was contributing writer for Space.com (opens in new tab) for 10 years before that, since 2012. As a proud Trekkie and Canadian, she also tackles topics like diversity, science fiction, astronomy and gaming to help others explore the universe. Elizabeth's on-site reporting includes two human spaceflight launches from Kazakhstan, three space shuttle missions in Florida, and embedded reporting from a simulated Mars mission in Utah. She holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, and a Bachelor of Journalism from Canada's Carleton University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Her latest book, Leadership Moments from NASA, is co-written with astronaut Dave Williams. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.