Giotto was the first solar system exploration mission carried out by the European Space Agency. Its objective was to image and analyze the nucleus of Halley's Comet and to study other characteristics of the comet during its next periodic swing through the inner solar system in 1986. The spacecraft was launched by an Ariane rocket on July 2, 1985. Data from the Soviet Vega spacecraft, which also investigated Halley's Comet, enabled Giotto's controllers to home in on the comet's nucleus. In its approach to the nucleus, Giotto returned a wealth of scientifically valuable data, including vivid images. It determined that the comet was 80 percent water, with a dust-covered, uneven surface darker than coal, and that the comet was composed of primitive material dating from the formation of the solar system.

Fourteen seconds before closest approach, Giotto was hit by a large particle ejected from the comet nucleus; this caused loss of data from the spacecraft and damaged some of its instruments, but others survived with little or no damage. The surviving instruments allowed Giotto, after "hibernating" for more than six years, to carry out a July 10, 1992, close encounter with the nucleus of Comet Grigg-Skjellerup. Giotto, no longer returning data, remained in orbit around the Sun.