PASADENA, Calif. — The spacecraft's technology is laughable by today's standards: It carries an 8-track tape recorder and computers with 240,000 times less memory than a low-end iPhone. When it left Earth 36 years ago, it was designed as a four-year mission to Saturn, and everything after that was gravy.
But Voyager 1 has become — unexpectedly — the Little Spacecraft That Could. On Thursday, scientists declared that it had become the first man-made object to exit the solar system, a breathtaking achievement that NASA could only fantasize about back when it was launched in 1977, the same year that Star Wars was released.
"I don't know if it's in the same league as landing on the moon, but it's right up there — Star Trek stuff, for sure," said Donald A. Gurnett, a professor of physics at the University of Iowa and the co-author of a paper published Thursday in the journal Science about Voyager's feat. "I mean, consider the distance. It's hard even for scientists to comprehend."
Even among planetary scientists, who tend to dream large, the idea that something they built could travel so far for so long and pierce the sun's reach is an impressive one. Plenty of telescopes gaze at the far parts of the Milky Way, but the plutonium-powered Voyager 1 can now touch and feel this unexplored region and send back detailed dispatches.
The lonely probe, which is 11.7 billion miles from Earth and hurtling away at 38,000 mph, has long been on the verge of bursting through the heliopause, the boundary between our solar system and interstellar space.
After much scientific debate, it is official that Voyager 1 passed into the cold, dark, unknown vastness of interstellar space, a place full of dust, plasma and other matter from exploded stars. The article in Science pinpointed a date: Aug. 25, 2012.
Coincidentally, the same month that Voyager 1 left the solar system, NASA's state-of-the-art rover Curiosity landed on Mars and started sending home gorgeous snapshots. Soon afterward, Curiosity's exploration team, some 400 strong, dazzled the world by driving the $2.5 billion robot across a patch of Martian terrain.
Voyager, meanwhile, stopped sending home pictures in 1990, to conserve energy. (Among its last photos was the famous "Pale Blue Dot," an image taken of Earth from nearly 4 billion miles away.) In its heyday, it pumped out never-before-seen images of Jupiter and Saturn, but lately there has not been much to see.
And the aging spacecraft's instruments have been breaking down for decades. An instrument that measures the energy of particles in plasma stopped working in 1980. But scientists still have access to a related sensor, a spindly antenna that records electron oscillations in plasma. The catch is that these oscillations don't occur all the time; they typically happen when stirred up by a solar eruption.
Voyager 1's plasma wave antenna picked up audible vibrations in April and May that allowed Gurnett and his colleagues to calculate the density of the plasma around the spacecraft, which would help them determine whether the craft was still in the solar system.
"It was exactly what we expected for interstellar plasma," Gurnett said.
Moreover, by combing through older oscillation data collected by Voyager 1, the team discovered that the edge of the solar system was roughly where Gurnett predicted it would be back in 1993 by using different solar storm calculations.
"Am I bragging here? No," he said. "All right. I admit it. It's bragging a little."