The Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, a satellite of the binary near-Earth asteroid (65803) Didymos, on 26 September 2022. Numerical simulations of the impact helped determine the physical properties of Dimorphos, including its low bulk density (less than 2,400 kg/m³), low boulder volume fraction (less than 40 vol%), and weak cohesive strength (less than a few pascals). These properties are similar to those of asteroids Ryugu and Bennu. The simulations suggest that Dimorphos is a rubble pile formed through rotational mass shedding and reaccumulation from Didymos. The DART impact caused global deformation and resurfacing of Dimorphos, and the ESA Hera mission may find a reshaped asteroid rather than a well-defined crater. The DART impact reduced Dimorphos's orbital period around Didymos by 33 minutes, indicating a momentum transfer to Dimorphos that exceeded the incident momentum of the DART spacecraft by a factor β ranging from 2.2 to 4.9. β is defined as the ratio of the target momentum increment after the impact to the impactor momentum, and is related to the additional thrust from the production of impact ejecta. β strongly depends on impact conditions and target material properties, such as strength, porosity, bulk density, and surface structure. The simulations showed that the DART impact caused a large amount of ejecta to be released, with the ejected material forming a wide ejecta cone. The observed ejecta cone opening angle and morphology suggest that Dimorphos has a low cohesion, consistent with a rubble pile structure. The results also indicate that the surface and shallow subsurface of Dimorphos have a low volume fraction of boulders larger than 2.5 m, which is consistent with data measured by the DART experiment. The study provides insights into the formation and characteristics of binary asteroid systems, suggesting that Dimorphos may have formed through rotational mass shedding and reaccumulation from Didymos. The findings also highlight the importance of understanding the physical properties of asteroids for planetary defense and future exploration missions. The results of this study will inform future exploration and asteroid deflection efforts.The Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, a satellite of the binary near-Earth asteroid (65803) Didymos, on 26 September 2022. Numerical simulations of the impact helped determine the physical properties of Dimorphos, including its low bulk density (less than 2,400 kg/m³), low boulder volume fraction (less than 40 vol%), and weak cohesive strength (less than a few pascals). These properties are similar to those of asteroids Ryugu and Bennu. The simulations suggest that Dimorphos is a rubble pile formed through rotational mass shedding and reaccumulation from Didymos. The DART impact caused global deformation and resurfacing of Dimorphos, and the ESA Hera mission may find a reshaped asteroid rather than a well-defined crater. The DART impact reduced Dimorphos's orbital period around Didymos by 33 minutes, indicating a momentum transfer to Dimorphos that exceeded the incident momentum of the DART spacecraft by a factor β ranging from 2.2 to 4.9. β is defined as the ratio of the target momentum increment after the impact to the impactor momentum, and is related to the additional thrust from the production of impact ejecta. β strongly depends on impact conditions and target material properties, such as strength, porosity, bulk density, and surface structure. The simulations showed that the DART impact caused a large amount of ejecta to be released, with the ejected material forming a wide ejecta cone. The observed ejecta cone opening angle and morphology suggest that Dimorphos has a low cohesion, consistent with a rubble pile structure. The results also indicate that the surface and shallow subsurface of Dimorphos have a low volume fraction of boulders larger than 2.5 m, which is consistent with data measured by the DART experiment. The study provides insights into the formation and characteristics of binary asteroid systems, suggesting that Dimorphos may have formed through rotational mass shedding and reaccumulation from Didymos. The findings also highlight the importance of understanding the physical properties of asteroids for planetary defense and future exploration missions. The results of this study will inform future exploration and asteroid deflection efforts.