Dimorphos is a small asteroid satellite that was discovered in 2003. It is the minor-planet moon of a synchronous binary system with 65803 Didymos as the primary asteroid. After being provisionally designated as S/2003 1 with informal nicknames such as "Didymos B" and "Didymoon", the Working Group Small Body Nomenclature of the International Astronomical Union gave the satellite its official name on 23 June 2020. At a diameter of 170 metres, it is one of the smallest astronomical objects that has been given a permanent name. Dimorphos is the target of NASA's Double Asteroid Redirection Test, a mission spacecraft which was launched on 24 November 2021 with a planned impact between 26 September and 1 October 2022. The DART mission is a test of planetary defence against asteroids. A flyby mini-satellite named LICIACube, provided by the Italian Space Agency, will photograph the collision. The European Space Agency's Hera mission will observe the asteroid after the impact.