Overview
This lecture explores the origins, achievements, and eventual fate of the Voyager 1 and 2 probes, highlighting their journey from launch to their interstellar mission and the legacy they represent for humanity.
The Voyager Probes: Launch and Mission
- Voyager 2 launched August 20, 1977, followed by Voyager 1 on September 5, 1977, exploiting a rare planetary alignment.
- Gravitational slingshot maneuvers with Jupiter, Saturn, Uranus (Voyager 2), and Neptune maximized speed and minimized fuel use.
- Primary missions included flybys of outer planets and their moons; Voyager 2 uniquely visited Uranus and Neptune.
Achievements and Interstellar Travel
- After completing planetary missions, both probes entered the "interstellar mission" phase, leaving the solar system.
- Voyager 1 crossed the heliopause in 2012, officially entering interstellar space; Voyager 2 followed in 2018.
- At the end of June 2025, Voyager 1 was 167.75 AU from the Sun, Voyager 2 at 140 AU, both traveling thousands of miles per hour.
The Golden Record: Humanity’s Message
- Both Voyagers carry a Golden Record with sounds, music, images, and greetings from Earth in 55 languages.
- The record's creation faced controversy over human nudity and musical selections, omitting many cultural symbols and genres.
- The disc also features a map to Earth's location using pulsars and hidden Morse code messages.
Longevity, Hazards, and Technical Challenges
- Nuclear generators power the probes, but decay reduces output by 4 watts/year.
- Cosmic rays and interstellar dust threaten probe functionality and physical integrity, causing occasional technical failures.
- Engineers have extended probe operations through creative workarounds despite aging hardware.
The Probes' Future Trajectories
- Probes will physically persist for millions or billions of years, but functionality will end by the 2030s.
- Mathematical predictions chart stellar flybys: Voyager 1 will pass close to Gliese 445 in 44,000 years; Voyager 2 near Ross 248 in 42,000 years.
- Both will eventually orbit the Milky Way multiple times as silent relics.
The Probability of Discovery by Aliens
- Latest estimates suggest only 36 technologically advanced civilizations exist in the galaxy, separated by ~17,000 light-years.
- Probability of the Voyager probes being found and interpreted by aliens is effectively zero due to immense interstellar distances and probe speed limits.
Symbolism and Legacy
- The Voyager probes symbolize humanity’s enduring desire to explore and leave a legacy, continuing their journey long after human civilization may end.
- They carry our message into the cosmos, likely never received, but still representing our will to reach beyond.
Key Terms & Definitions
- Heliopause — the boundary where the Sun’s solar wind stops affecting space, marking entry into interstellar space.
- Gravitational slingshot — using a planet’s gravity to accelerate a spacecraft and change its trajectory.
- Golden Record — a gold-plated copper disc aboard each Voyager, containing sounds and images to represent Earth.
- Cosmic rays — high-energy charged particles from space that can damage spacecraft electronics.
- Astronomical Unit (AU) — average distance between Earth and the Sun, about 93 million miles (150 million km).
Action Items / Next Steps
- Review diagrams of the Voyager trajectories and their planned stellar encounters.
- Read more about the Golden Record’s contents and controversies.
- Study the physics of interstellar space and cosmic rays for further understanding.