If an incoming asteroid were to threaten Earth, what could people do about it? On 26 September 2022 NASA’s DART mission performed humankind’s first test of asteroid deflection by crashing into the Great-Pyramid-sized Dimorphos moonlet. The result was a shift in its orbit around the mountain-sized Didymos main asteroid.

Next comes ESA’s own contribution to this international collaboration: the Hera mission will revisit Dimorphos to gather vital close-up data about the deflected body, to turn DART’s grand-scale experiment into a well-understood and potentially repeatable planetary defence technique.

The mission will also perform the most detailed exploration yet of a binary asteroid system – although binaries make up 15% of all known asteroids, they have never been surveyed in detail. Hera will also perform technology demonstration experiments, including the deployment ESA’s first deep space ‘CubeSats’ – shoebox-sized spacecraft to venture closer than the main mission then eventually land – and an ambitious test of 'self-driving' for the main spacecraft, based on vision-based navigation.