An illustration of the Voyager spacecraft doing what it does best: voyaging.

NASA’s Voyager 1 spacecraft has reached the edge of the solar system. It took 33 years to get there, but it is now the farthest man-made object from Earth. It’s currently hurtling through the doldrums at the outskirts of the solar system where the speed of the solar wind emanating from the Sun slows to zero as it crashes into an opposing wall of interstellar wind. NASA estimates that Voyager 1 may break out of this dead zone, known as the heliosheath, and exit the solar system into true interstellar space within four years.

Voyager 2, an identical spacecraft launched in 1977 a few weeks before Voyager 1, is moving on a longer trajectory but will also eventually leave the solar system. During their 33 year journey the Voyager spacecraft have provided us with up-close views of Jupiter, Saturn, Uranus, and Neptune. And despite their advanced age, NASA expects the instruments aboard each spacecraft will continue to relay new information to us for another 25 years before the spacecrafts’ power supplies fail. As the Voyagers prepare to move into interstellar space, it seems like a good time to take a look back at what they’ve seen during their journey so far. [images: NASA/JPL]

Voyager 1 took this image of a crescent Earth and Moon as it sped away from the Earth, 7.25 million miles out.

Jupiter was the Voyagers’ first stop. Taking advantage of a special alignment of the planets, both spacecraft were able to reach Jupiter by 1979, less than two years after their launch. Two moons can be seen in this image of Jupiter, taken as Voyager 1 approached the planet.

Saturn gets a lot of attention for its large, flashy rings, but Voyager 1 discovered that Jupiter has a ring of its own, albeit a more modest one, shown here in a false-color image taken by Voyager 1. The ring is composed mainly of dust that has been kicked off of Jupiter’s numerous moons by meteor impacts.

The Voyagers also took a look at some of Jupiter’s moons as they flew past. NASA scientists were surprised to learn that Jupiter’s moon Io is volcanically active when Voyager 1 captured this image of an erupting volcano on Io’s surface. The massive greenish-white volcanic plume seen here is 100 miles high. We now know that Io is the most volcanically active object in the solar system. Its volcanoes are the result of tides, but not the sort of tides we’re used to. As Io orbits Jupiter the intense gravitational pull of the planet and its other massive moons creates bulges in Io’s crust up to 100 meters high. The pressure created by these tides is released in massive volcanic explosions. Although the volcanic vents themselves are very hot, the rest of Io is very cold, so scientists suspect that the volcanic plumes observed by the Voyagers are made of sulfur dioxide snow, which exits the volcanoes as a gas but quickly freezes.

Voyager 2 recorded this shot of Saturn as it approached the planet in 1981. Two of Saturn’s moons are visible in the foreground.

Voyager 2 took this false-color image of a segment of Saturn’s rings. The rings are mainly composed of chunks of water ice, and, to a lesser extent, dust.

As Voyager 2 flew past Uranus in 1986, it provided us with a closer look at some of the planet’s moons and even detected 10 previously unknown Uranian moons. The Uranian moon Miranda, shown here, was found to have surprisingly rugged and varied terrain, indicating a complicated geological past.

Voyager 2 took this farewell shot of a crescent Uranus as it sped away from the planet in 1986.

Voyager 2 flew past Neptune in 1989, recording this image as it approached the planet. The dark spots on the surface of the planet are massive storms with winds reaching 1500 miles per hour, the most intense winds in the solar system. The storms come and go and change position every few years. The white spots are clouds in Neptune’s upper atmosphere.

In 1990 Voyager  1 turned its cameras around and took this humbling picture of Earth from 3.7 billion miles away. The bands of color in the photograph are the result of sunlight scattering through the camera lens. Earth appears as a blue dot within the red light band in the upper right corner of the image. Reflecting on this image Carl Sagan wrote:

“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. Our planet is a lonely speck in the great enveloping cosmic dark.”

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