Surface feature tracing

The tracing of asteroid surface features is the technique ESA's Hera mission will use to navigate around the Didymos system. The mass of Didymoon will also be measured by observing the so-called ‘wobble’ of its parent ‘Didymain’ asteroid. Hera will achieve this by selecting a key landmarks, such as boulders, on the larger asteroid surface then tracking their motion around the centre of mass of the overall asteroid system.