A US spacecraft launched in 1977 has reached the final frontier at the edge of the solar system.
Scientists say Voyager 1 has entered a "new region" which could be its gateway to interstellar space.
The border area is described as a "magnetic highway" for outgoing charged particles from the sun and incoming particles from the stars.
"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 project scientist Dr Edward Stone from the California Institute of Technology in Pasadena.
"We believe this is the last leg of our journey to interstellar space. Our best guess is it's likely just a few months to a couple of years away."