PASADENA, Calif. (AP) -- Thirty-five years after leaving Earth, Voyager 1 is reaching for the stars.
Sooner or later, the workhorse spacecraft will bid adieu to the solar system and enter a new realm of space -- the first time a manmade object will have escaped to the other side.
When NASA's Voyager 1 and Voyager 2 first rocketed out of Earth's grip in 1977, no one knew how long they would live.
Now, they are the longest-operating spacecraft in history and the most distant, at billions of miles from Earth but in different directions.
Wednesday marks the 35th anniversary of Voyager 1's launch to Jupiter and Saturn. It is now flitting around the fringes of the solar system, which is enveloped in a giant plasma bubble.
Outside the bubble is a new frontier in the Milky Way -- the space between stars. Once it plows through, scientists expect a calmer environment by comparison.
When that would happen is anyone's guess. Voyager 1 is in uncharted celestial territory.
Voyager 1 is currently more than 11 billion miles from the sun. Twin Voyager 2, which celebrated its launch anniversary two weeks ago, trails behind at 9 billion miles from the sun.
They're still ticking despite being relics of the early Space Age.
The Voyagers' original goal was to tour Jupiter and Saturn, and they sent back postcards of Jupiter's big red spot and Saturn's glittery rings.
They also beamed home a torrent of discoveries: erupting volcanoes on the Jupiter moon Io; hints of an ocean below the icy surface of Europa, another Jupiter moon; signs of methane rain on the Saturn moon Titan.
Since 2004, Voyager 1 has been exploring a region in the bubble at the solar system's edge where the solar wind dramatically slows and heats up. Over the last several months, scientists have seen changes that suggest Voyager 1 is on the verge of crossing over.
When it does, it will be the first spacecraft to explore between the stars.
Space observatories such as the Hubble and Spitzer space telescopes have long peered past the solar system, but they tend to focus on far-away galaxies.