Rosetta became the first spacecraft to orbit a comet when it reached comet 67P/Churyumov–Gerasimenko in 2014.
The European Space Agency launched Rosetta in 2004. After a decade-long journey that included gravity assists and a long hibernation, it entered orbit around 67P on 6 August 2014. The spacecraft mapped the comet’s nucleus, studied its coma and jets, and observed how activity increased as sunlight warmed the surface.
Rosetta also carried the Philae lander, which made the first landing on a comet nucleus in November 2014. Philae bounced after its initial touchdown because its anchoring system failed, but it still returned important measurements from the surface.
Rosetta is distinct from earlier comet missions such as Giotto, which performed a flyby of Halley’s Comet. Rosetta’s defining achievement was sustained orbital study rather than a brief encounter.