Dimorphos has a diameter of 177 meters (581 ft) across its longest extent and it was the target of the Double Asteroid Redirection Test (DART), a NASA space mission that deliberately collided a spacecraft with the moon on 26 September 2022 to alter its orbit around Didymos.

[23][15][24] Post-impact observations of brightness fluctuations within the Didymos system suggest that the impact may have either significantly deformed Dimorphos into an ellipsoidal shape or may have sent it into a chaotically tumbling rotation.

[1] The satellite Dimorphos was discovered on 20 November 2003, in photometric observations by Petr Pravec and colleagues at the Ondřejov Observatory in the Czech Republic.

[28][13] The Working Group for Small Bodies Nomenclature of the International Astronomical Union (IAU) gave the satellite its official name on 23 June 2020.

[2] The name was suggested by Kleomenis Tsiganis, a planetary scientist at the Aristotle University of Thessaloniki and a member of both the DART and Hera teams.

[32] On 24 November 2021, NASA and the Applied Physics Laboratory launched an impactor spacecraft towards Dimorphos as part of their Double Asteroid Redirection Test (DART).

[37][29][38][39] Fifteen days prior to its collision, the impactor released LICIACube, an Italian Space Agency CubeSat that photographed the impact and the resulting dust plume as it performed a close flyby of the Didymos system.

[33][40][41][42] Spacecraft and observatories such as Hubble, James Webb, Lucy, SAAO and ATLAS also captured the dust plume trailing the Didymos system in the days following the impact.

Researchers found the impact caused an instantaneous slowing in Dimorphos' speed along its orbit of about 2.7 millimeters per second — again indicating the recoil from ejecta played a major role in amplifying the momentum change directly imparted to the asteroid by the spacecraft.

[2] The final few minutes of pictures from the DART mission revealed an egg-shaped body covered with boulders, suggesting it has a rubble pile structure.

They are approximately 10 meters across or smaller:[58] The primary body of the binary system, Didymos, orbits the Sun at a distance of 1.0 to 2.3 AU once every 770 days (2 years and 1 month).