Which spacecraft was the first to orbit Jupiter?

Galileo was the first spacecraft to orbit Jupiter.

NASA launched Galileo on 18 October 1989 aboard Space Shuttle Atlantis. Instead of traveling directly to Jupiter, it used gravity-assist flybys of Venus and Earth to gain speed and conserve propellant. Galileo reached Jupiter in December 1995 and entered orbit around the giant planet.

The spacecraft released an atmospheric probe that descended into Jupiter’s clouds, measuring temperature, pressure, composition, and winds before its signal ended. Galileo also studied Jupiter’s major moons, producing especially important evidence that Europa may contain a liquid ocean beneath its icy surface.

Pioneer 10 was the first spacecraft to fly past Jupiter, while Voyager 1 and Voyager 2 later performed celebrated flybys. Those missions did not enter orbit, which is why Galileo holds the orbital milestone. NASA deliberately sent Galileo into Jupiter in 2003 to avoid an accidental impact with Europa.