Which spacecraft was first to enter interstellar space?

Which spacecraft was first to enter interstellar space? Voyager 1. NASA’s Voyager 1 became the first human-made spacecraft to enter interstellar space, crossing the heliopause on August 25, 2012.

Voyager 1 launched on September 5, 1977, shortly after Voyager 2. A faster trajectory carried it past Jupiter in 1979 and Saturn in 1980, after which it headed outward on a path away from the planets. Its instruments detected changes in charged particles and plasma that showed it had left the Sun’s heliosphere.

Interstellar space begins beyond the heliopause, where the solar wind no longer dominates. Voyager 1 crossed that boundary roughly 122 astronomical units from the Sun, although it remains gravitationally associated with the Milky Way rather than leaving the galaxy.

Voyager 2 also entered interstellar space, but later, in November 2018. New Horizons has traveled far beyond Pluto, yet it has not been the first spacecraft to cross the heliopause. Pioneer 10 was an earlier deep-space pioneer but did not reach interstellar space first.