End of an era
Voyager also closed a contentious chapter in astronomy history by revising Neptune’s mass downward by around half a percent — or roughly the mass of Mars. This miscalculation had sent astronomers on a wild goose chase through the years as they tried to make sense of Uranus’ and Neptune’s orbits, usually by invoking the existence of a mysterious Planet X tugging on both of them. (Pluto was found as a direct result of this hunt, but its small size was never enough to resolve the initial problem.) Voyager settled the issue, as Neptune’s smaller mass means it and Uranus orbit just as they should.
To mark the final flyby, NASA’s Jet Propulsion Laboratory hosted a special event celebrating Voyager’s journey and accomplishments. Scientists shared images with the public, and rock-’n’-roll legend Chuck Berry, whose music lives on as part of Voyager’s Golden Record, played in a special concert.
At the edge of our planetary system, 2.75 billion miles (4.43 billion km) from Earth, Voyager turned its cameras back for a last look, imaging farewell shots of a crescent Neptune. Dodd recalls her reaction to the images: “Wow. The planetary mission is done. We’re going off into the deep dark and cold realms of space. Who knows how long the mission will last?”
Epilogue
When she left her position with the Neptune team, Dodd says, no one then imagined Voyager would continue as long as it has. She returned to Voyager’s interstellar mission in 2010, 21 years after she left the project. In many ways, she admits that the spacecraft is an artifact — memory and power limited, with many of its specialists long since retired or passed on. Since Voyager’s departure from Neptune, many of its instruments have gone quiet. There is no need for imaging cameras in the dark void of space. But that does not mean the project is defunct.
Voyager continues to measure magnetic fields, charged particles, plasma density, and more as it cruises the solar system’s hinterlands, teaching scientists about the subtle edges of the solar system’s boundaries. Voyager 1 has passed beyond the reach of the solar wind, and thus is sampling aspects of interstellar space, though it still lies well within the Sun’s gravitational influence. Voyager 2, following a slower trajectory from its two-planet detour, tags behind, still sampling the solar wind. From their distance, it takes more than 15 hours for their signals to reach Earth.
Sometime in the next decade, the spacecraft will lose power and begin to shut down. Dodd’s team will turn the Voyagers’ heaters off first, and one by one, the science instruments will succumb to the cold of space. But the spacecraft themselves and their Golden Records will journey on, carrying humanity’s imprint into the cosmos.
It will be years before any spacecraft retreads Voyager’s path to Uranus or Neptune. With at least half a century of technological advances behind it, any future craft will undoubtedly revolutionize our understanding of the ice giants all over again. But it’s safe to say that nothing will match Voyager for sheer adventure and scope. Decades after its primary mission, Voyager continues to teach, to inspire, and to explore.