Step by Step
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Launch and the Grand Tour
Voyager 1 and 2 launched in 1977, taking advantage of a rare planetary alignment that occurs only once every 175 years. Both visited Jupiter and Saturn; Voyager 2 alone continued on to Uranus and Neptune, making it the only spacecraft ever to visit those two planets.
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Key discoveries
The Voyager missions discovered Io's active volcanoes, hints of a subsurface ocean on Europa, one of Jupiter's rings, and the ring systems around Uranus.
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Interstellar space and the Golden Record
Voyager 1 crossed the heliopause into interstellar space in 2012, and is now roughly 23 billion km from Earth — the farthest human-made object ever. Both spacecraft carry a Golden Record, containing greetings, music, and images intended for any intelligent life that might one day encounter them.
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Power source and the mission's eventual end
Both Voyagers are powered by a plutonium RTG (radioisotope thermoelectric generator), which converts heat from radioactive decay into electricity — and remarkably, this power source is still functioning today. Their signals are expected to weaken beyond detectability sometime between 2025 and 2030.
Applied Walkthrough
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Launched in 1977 during a rare planetary alignment occurring only once every 175 years, Voyager 1 and 2 embarked on a "Grand Tour" of the outer solar system, both visiting Jupiter and Saturn.
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Voyager 2 alone continued onward, becoming the only spacecraft ever to visit both Uranus and Neptune — along the way, the two spacecraft together discovered Io's active volcanoes, hints of Europa's subsurface ocean, and previously unknown rings around Jupiter and Uranus.
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In 2012, Voyager 1 crossed the heliopause, officially entering interstellar space — now roughly 23 billion km from Earth, it remains the farthest human-made object in existence, still carrying its Golden Record of greetings, music, and images for any intelligent life that might one day find it.
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Powered by a plutonium RTG that converts radioactive decay heat into electricity, both Voyagers remarkably continue transmitting data back to Earth even today, nearly five decades after launch — though their signals are expected to finally weaken beyond detectability sometime between 2025 and 2030.
Exam Application
Exams test whether you know the Voyager missions' launch year and the rare planetary alignment that made the Grand Tour possible, whether you know which spacecraft visited which outer planets (specifically that only Voyager 2 visited Uranus and Neptune), and whether you know the significance of the 2012 interstellar space crossing.
⚠ Common Trap
The most common trap is assuming both Voyager 1 and Voyager 2 visited all four outer planets — only Voyager 2 continued on to visit Uranus and Neptune, making it the only spacecraft to have visited those two planets; Voyager 1 visited only Jupiter and Saturn before heading toward interstellar space.
✓ Quick Self-Check
1. When did Voyager 1 and 2 launch, and what rare event made their trajectory possible?
1977, taking advantage of a rare planetary alignment occurring once every 175 years.
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2. Which spacecraft visited Uranus and Neptune, and is it the only one to have done so?
Voyager 2 — yes, it's the only spacecraft to have visited both.
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3. When did Voyager 1 enter interstellar space?
2012, crossing the heliopause.
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4. What is the Golden Record?
A record carried by both Voyager spacecraft containing greetings, music, and images intended for any intelligent life that might encounter them.
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5. What power source do the Voyager spacecraft use, and is it still functioning?
A plutonium RTG (radioisotope thermoelectric generator); yes, it's still functioning today.
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