Voyager 1 became the first spacecraft to leave the heliosphere

NASA launched Voyager 1 on September 5, 1977, expecting a grand tour of the outer planets. It delivered close-ups of Jupiter and Saturn, then aimed for the edge of everything.

On August 25, 2012, it became the first human-made object to cross the heliopause — the boundary where the Sun’s outward gust of charged particles surrenders to the thin gas between the stars. The crossing was confirmed not by a sign in space but by the instruments: the surrounding plasma density jumped sharply, exactly what you’d expect on leaving the Sun’s sparse bubble for the denser interstellar medium. Beyond that line, Voyager 1 was sampling an environment no probe had touched.

It had already claimed another title in 1998, overtaking Pioneer 10 as the most distant human-made object, and has never given it back. The craft now sits well over 160 times farther from the Sun than Earth, its signals taking many hours to arrive.

It carries the Golden Record, a gold-plated greeting holding spoken hellos in 55 languages, music, and the sounds of Earth; its cover is etched with a pulsar map pinpointing our location for any finder. In 1990, at Carl Sagan’s urging, Voyager 1 turned its camera back home and caught the Pale Blue Dot — Earth as a single faint pixel in a sunbeam.

Its plutonium radioisotope generators fade by about 4 watts a year, so engineers switch off instruments one by one to ration the dwindling supply. Even with that careful husbandry, the spacecraft is expected to fall silent sometime in the 2030s, ending the longest conversation humanity has ever held.