Hera glides past Didymos to Dimorphos

Hera is an ESA mission that will be humankind’s first probe to rendezvous with a binary asteroid system, Didymos.

Didymos is a binary asteroid; the primary body has a diameter of around 780 m, whereas the Dimorphos secondary body has a diameter of around 160 m and rotates around the main asteroid at a distance of around 1.2 km.

Dimorphos was impacted by the NASA DART spacecraft on 26 September 2022, shifting its orbit around its parent. Returning to Dimorphos, Hera will perform a close-up survey of the asteroid moon to measure its mass, makeup and structure.

Hera will map Dimorphos’s entire surface down to a resolution of a few metres, and the surface surrounding the DART crater down to >10 cm resolution, through a series of daring flybys. It will also map much of the surface of the primary Didymos asteroid, providing crucial scientific data from two asteroids in a single mission.

A full picture of DART's kinetic impact and resulting momentum transfer will only become possible once Hera maps the mass of Dimorphos to a high level of certainty, turning DART's grand-scale experiment into a well understood and potentially repeatable planetary defence technique.