Happy 35th Birthday, Voyager!

Today, September 5, marks the 35th anniversary of the launch of Voyager 1, which lifted off in 1977 on a Titan III-Centaur launch system just 16 days after its twin, Voyager 2. Now 11 billion and 9 billion miles from the sun, respectively, the spacecraft are the farthest-flung man-made objects, traveling every 100 days a distance equal to that between sun and Earth. "We thought we could do this, but it is, in a certain sense, amazing," says Ed Stone, the mission's project scientist and the David Morrisroe Professor of Physics at Caltech. "After all, when the Voyagers were launched, the space age itself was only 20 years old." Originally commissioned to last just four years, the Voyager mission created two identical spacecraft—with the hope that at least one would reach Jupiter and Saturn. As we now know, both Voyager spacecraft survived launch and the harsh radiation environment around Jupiter to relay close-up images and scientific measurements of the outer solar system's planets and their moons. "There was much more out there to be discovered than we could have possibly imagined," says Andrew Ingersoll, an atmospheric scientist on the Voyager team and professor of planetary science at Caltech. "There were many heroes on the Voyager mission, but I like to say that the planets themselves were among those.