After a 35-year, 13-billion mile journey, NASA's Voyager 1 spacecraft has become the first human-made object to reach interstellar space, new evidence from a team of scientists shows.
"It's kind of like landing on the moon. It's a milestone in history. Like all science, it's exploration. It's new knowledge," long-time Voyager scientist Donald Gurnett, with the University of Iowa, told Discovery News.
PHOTOS: Voyager 2's Outer Solar System Odyssey
In the end, it was the sun itself that in essence "rang Voyager's bell," providing the definitive proof that had eluded scientists for the past year or so about whether or not the spacecraft had reached the space between the stars.
On Aug. 25, 2012, Voyager, which was launched in 1977 to study the outer planets, detected a sudden drop in the number of particles trapped in the bubble of space under the sun's influence, the so-called heliosphere, and a corresponding spike in the number of galactic cosmic rays from outside the solar system.
That evidence alone, however, was not enough to convince scientists Voyager had finally reached interstellar space. What they really wanted to know was how much plasma -- ionized molecules and atoms -- was around Voyager, but that measurement was not possible since the spacecraft's plasma detector stopped working more than 30 years ago.