Hera scans DART’s impact crater

Hera is a candidate 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 Didymoon secondary body has a diameter of around 160 m and rotates around the main asteroid at a distance of around 1.2 km. Didymoon will be impacted by the NASA DART spacecraft in October 2022. Its orbital velocity is expected to be shifted by around half a millimetre per second, changing its rotation period enough to be measured roughly with Earth-based telescopes. At the same time DART’s collision will also leave a 20-metre-wide crater on Didymoon’s surface. Hera will map the shape of this crater to gather unique information to design asteroid deflection missions in future. In addition, the mission will shed light on the asteroid’s surface properties and internal structure. Is the asteroid a monolithic mass or a rubble pile? Is it composed of large or tiny grains? Is the subsurface composition identical to the surface one?