Two 1970s Spacecraft Are Still Phoning Home From Interstellar Space
NASA launched Voyager 1 and 2 in 1977 with computers weaker than a digital watch. Half a century later, both are still operating — over 23 billion kilometers from Earth, beyond the boundary of the solar system.
In 1977, NASA launched two spacecraft on similar trajectories: Voyager 1 and Voyager 2. The mission's goal was a tour of the outer planets. By 1989, they had photographed Jupiter, Saturn, Uranus, and Neptune at close range, sending back the first detailed images of the solar system's giants.
Then they kept going.
Voyager 1 crossed the heliopause in 2012 — the boundary where the Sun's solar wind ends and interstellar space begins. Voyager 2 followed in 2018. Both are now in true interstellar space.
The spacecraft's onboard computers run on a few kilobytes of memory. The signal beamed back to Earth has the strength of about 20 watts — less than a refrigerator bulb — and arrives spread thin across an antenna 22 hours of light travel away. By the time the signal reaches NASA's Deep Space Network, it has weakened by a factor of a quintillion. Massive ground antennas, hundreds of meters across, listen for the whisper.
Each Voyager carries a Golden Record: a 12-inch gold-plated copper disk encoded with greetings in 55 languages, sounds of Earth — surf, thunder, a baby crying — and 90 minutes of music ranging from Beethoven to Chuck Berry. A diagram on the cover shows extraterrestrials how to play it.
Power comes from plutonium. As the plutonium decays, less heat is available, and instruments are switched off one at a time to keep what remains running. NASA expects the last instrument to fall silent around 2036.
After that, the Voyagers will continue drifting outward — silent, alone, possibly forever — carrying our message to anyone who finds them.