Scientists have dubbed the region a "magnetic highway" where charged particles where our sun's magnetic field lines are connected to interstellar magnetic field lines, the space agency said.
The Voyager science team said it consider this region as still being inside our solar system because the direction of the magnetic field lines has not changed.
When Voyager breaks through to interstellar space, they said, these magnetic field lines are predicted to change.
"Although Voyager 1 still is inside the sun's environment, we now can taste what it's like on the outside because the particles are zipping in and out on this magnetic highway," said Edward Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. "We believe this is the last leg of our journey to interstellar space."
Voyager 1, launched in 1977, is now the most distant human-made object, about 11 billion miles away from the sun.