NASA - Voyager Mission patch.
Sept. 5, 2017
The twin Voyager 1 and 2 spacecraft are still operating and traveling where no spacecraft – or anything touched by humanity – has gone before. As we approach the 40th anniversary of the Voyager 1 launch on Sept. 5, we reflect on the vision that inspired the mission, its greatest achievements, and its enduring legacy.
Image above: This artist's concept depicts NASA's Voyager 1 spacecraft entering interstellar space, or the space between stars. Image Credits: NASA/JPL-Caltech.
In August of 2012, Voyager 1, after travelling more than 12 billion miles, left our solar system and entered interstellar space. Voyager 2, now more than 10 billion miles from Earth, is expected to join its pioneering twin in interstellar space within the next few years. Forty years after their successive launches, the Voyagers visited more planets, discovered more moons, and imaged more unique places than any other spacecraft in NASA history.
As the first spacecraft to fly by all four giant planets in the outer solar system, Voyager produced a bonanza of new science. Among the mission’s many accomplishments:
- Only spacecraft to visit Uranus and Neptune (Voyager 2) and first to image the rings of Jupiter, Uranus and Neptune
- First spacecraft to discover active volcanoes beyond Earth (Io) and multiple moons of the four outer planets: three new moons at Jupiter, four at Saturn, 11 at Uranus and five at Neptune
- First detection of lightning on a planet other than Earth (at Jupiter) and first suggestion of ocean beyond Earth (beneath the icy crust at Europa)
Voyager paved the way for a number of NASA missions. The Galileo and Juno missions to Jupiter and Cassini at Saturn had their origins in Voyager science. Data from the Voyagers revealed Jupiter’s turbulent atmosphere. Today, and as a result of the Voyager’s previews, our Juno spacecraft observes Jupiter’s storms at very close range and has found almost Earth-sized cyclones at both polar caps.
Image above: NASA Director of Planetary Science James L. Green. Image Credit: NASA.
The Europa Clipper mission, now under development, is an orbiter that will build on Voyager’s experience. Clipper is scheduled to launch in the early 2020s, and its potential successor – a Europa lander – would be a logical successor for Europa exploration, seeking evidence of life beyond Earth. Voyager discoveries also inspired a future mission back to Jupiter’s fascinating volcanic moon Io, with an Io Observer listed as one of the key science priorities in NASA’s New Frontiers line of missions in February 2007.
At Saturn, the complexity and variety of the structure in the Saturn ring systems, as revealed by Voyager, came as a complete surprise. Saturn’s bizarre hexagonal-shaped storm at the north pole was observed for the first time. Titan was revealed to be an orange ball with a smoggy atmosphere so dense that the surface could not be imaged.
The ice giants Uranus and Neptune have been unexplored since Voyager 2 flew by Uranus in 1986 and Neptune in 1989, but that could change in the years ahead. The current Planetary Science Decadal Survey, which covers 2013-2022, lists a return to Uranus or Neptune as a future priority.
Image above: This gold aluminum cover was designed to protect the Voyager 1 and 2 "Sounds of Earth" gold-plated records from micrometeorite bombardment. Image Credit: NASA.
Voyager 2 performed a very close flyby about 3,000 miles (5,000 kilometers) above the Neptune’s north polar cloud tops to observe Neptune’s moon Triton. This was the closest trajectory to any of the outer planets and initiated the development of precision trajectories in order to support very close flybys. Today, Cassini has flown through the plumes of Saturn’s icy moon Enceladus just 10 miles (15 kilometers) above the surface. This gutsy approach can be traced back to the success of the very close flyby of Neptune accomplished by Voyager 2 to observe Triton.
Critical to the success of the Voyager outer planet tour was the principle of gravity assist. Voyager 2 nailed the gravity assist to tour Jupiter, Saturn, Uranus and Neptune. Since then, a number of missions have employed gravity assists to save fuel and dramatically reduce the amount of time it takes to get to destinations in the outer solar system. While the Voyagers’ “Grand Tour” didn’t include Pluto, a gravity assist from Jupiter sent our New Horizons spacecraft past Pluto in July of 2015, completing the initial reconnaissance of the solar system. OSIRIS-REx will get a gravity assist from Earth on Sept. 22 to accelerate the spacecraft to the asteroid Bennu. MESSENGER received assists at Earth and Venus, and three separate assists from Mercury itself before being placed into Mercury’s orbit. Cassini received two gravity kicks at Venus and one each at Earth and Jupiter on the way to Saturn.
The Voyager discoveries didn’t stop with planetary flybys. The Voyagers have an impressive list of accomplishments as the spacecraft continue their journey into the unknown:
- First spacecraft to leave the heliosphere and enter interstellar space in 2012 (Voyager 1)
- First measurement of full intensity of cosmic rays in interstellar space, galactic magnetic field in interstellar space, and density of interstellar medium (Voyager 1)
- First measurements of the solar wind termination shock (Voyager 2)
Beyond the transformative science, the Voyagers captured the world’s imagination with a time capsule of sorts on each spacecraft—the Golden Record. The Voyager’s twin phonograph records are filled with images and sounds to provide a snapshot of life and culture on Earth should the spacecraft ever come in contact with future space travelers. As Carl Sagan noted, “The launching of this ‘bottle’ in the cosmic ocean says something very hopeful about life on this planet.”
In my quieter moments, I think about a time – billions of years from now – when our Sun becomes a red giant, Earth is no longer habitable, and humans will have survived long enough to leave the nest for another home, following a path forged by the Voyager missions. It is humbling and inspiring to think that the Voyagers will still be Earth’s ambassadors—each a time capsule of an era when audacious explorers on our Pale Blue Dot left home for the outer reaches of our planetary system and on to the stars.
Related links:
Voyager: https://www.nasa.gov/mission_pages/voyager/index.html
Solar System: https://www.nasa.gov/topics/solarsystem/index.html
Images (mentioned), Animation (mentioned), Text, Credits: NASA/Tricia Talbert/By James L. Green, Director, NASA Planetary Science Division.
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