Beyond the Solar System — The Voyager Probes and the Golden Record
Launched in 1977, two small probes swept past the giant planets one by one on their way out of the Solar System. Here's the story of the Golden Record carrying humanity's greeting, and the journey that continues to this day.
Summer 1977, two probes depart
In the summer of 1977, NASA launched two robotic probes, Voyager 1 and Voyager 2, in quick succession. The launch took advantage of a rare alignment of the Solar System's four giant planets — Jupiter, Saturn, Uranus, and Neptune — that occurs only once about every 176 years. That alignment let the probes ride a "gravity assist," using each planet's gravity to slingshot toward the next on what became known as the "Grand Tour."
Both probes' missions originally targeted only Jupiter and Saturn, but they held up far better than expected — well enough that Voyager 2's mission was extended, making it the first spacecraft in history to fly past both Uranus and Neptune up close.
Sweeping past the giant planets
The Voyagers left remarkable discoveries wherever they passed. Flying by Jupiter, they captured the Solar System's first confirmed active volcanic eruption, on the moon Io, and raised the possibility of a hidden ocean beneath the icy surface of the moon Europa. At Saturn, they revealed that its famous rings weren't a few broad bands but thousands of thin, individual ringlets.
The images Voyager 2 brought back of Uranus and Neptune remain, to this day, the only close-up photographs ever taken of either planet. At Neptune in particular, it discovered an Earth-sized storm (the Great Dark Spot) and the ice-volcano moon Triton, bringing its planetary tour to a close.
The Golden Record — humanity's greeting to the stars
Each Voyager carries a gold-plated copper disc, the "Golden Record." Produced by a committee led by astronomer Carl Sagan, it holds greetings in 55 languages, sounds of nature and people from around Earth, music ranging from Bach and Beethoven to traditional pieces from many cultures, and pictorial instructions explaining how to play it.
The odds that another intelligent civilization will ever find either probe after it leaves the Solar System are vanishingly small — but the very act of sending humanity's sounds into space regardless made the Golden Record a symbolic work of art and a record of its era in its own right.
Beyond the heliosphere, into interstellar space
In 2012, Voyager 1 crossed the boundary where the solar wind's influence ends (the heliopause), becoming the first human-made object to enter "interstellar space." Its plutonium power source is expected to run out sometime around 2025, ending communication — but for now it still sends back faint signals from more than 24 billion kilometers away.
Even after its power fails, Voyager will keep drifting through our galaxy without stopping, carrying humanity's greeting on the Golden Record for hundreds of millions of years to come. This small probe that left Earth half a century ago remains the farthest handwritten letter our species has ever sent.