Voyager 1 became the first human-made object to enter interstellar space, crossing the heliopause in 2012.
NASA launched Voyager 1 on 5 September 1977 to study Jupiter and Saturn. It flew past Jupiter in 1979 and Saturn in 1980, using planetary gravity to alter its trajectory and gain speed. Its route then carried it outward from the Solar System.
The spacecraft crossed the heliopause, the boundary where the solar wind is overtaken by interstellar plasma, on 25 August 2012. Scientists identified the crossing from changes in plasma density and magnetic-field-related measurements. Voyager 2 crossed the same broad boundary in 2018 on a different trajectory.
Interstellar space does not mean Voyager 1 has left the Solar System completely; the distant Oort Cloud extends much farther. Voyager 1 remains a functioning spacecraft, though its available power and instruments have gradually declined.