NASA’s Galileo spacecraft made the first flyby of an asteroid, passing Gaspra in 1991.
Galileo flew past asteroid 951 Gaspra on October 29, 1991, while traveling toward Jupiter. The encounter produced the first close-up images of an asteroid, revealing an irregular, heavily cratered rocky body about 19 kilometers long. Galileo later flew past asteroid 243 Ida in 1993 and discovered Dactyl, the first confirmed moon of an asteroid.
The spacecraft launched in 1989 and reached Jupiter in December 1995. Its route used gravity assists at Venus and Earth to gain the energy needed for the outer Solar System, so Gaspra was an intermediate milestone rather than Galileo’s primary destination.
Galileo then studied Jupiter, its atmosphere, magnetosphere, and major moons for years. It was deliberately sent into Jupiter’s atmosphere in 2003 to avoid any chance of contaminating Europa, which may possess conditions favorable to life.