The ESA Hera mission: European contribution to the first asteroid deflection test

The Hera mission has been approved for development and launch in the new ESA Space Safety Programme by the ESA Council at Ministerial Level, Space19+, in November 2019. Hera will contribute to the first deflection test of an asteroid, in the framework of the international NASA- and ESA supported Asteroid Impact and Deflection Assessment (AIDA) collaboration. The impact of the NASA DART (Double Asteroid Redirection Test) spacecraft on the natural satellite of the binary asteroid Didymos in late September 2022 will change its orbital period around Didymos. As Didymos is an eclipsing binary, and close to the Earth on this date, the change can be detected by Earth-based observers. ESA's Hera spacecraft will rendezvous Didymos four years after the impact. While performing the measurements necessary to understand the effect of the DART impact on Didymos' secondary, in particular its mass, its internal structure, the direct determination of the momentum transfer and the detailed characterization of the crater left by DART, Hera will provide unique information on many current issues in asteroid science. From small asteroid internal and surface structures, through rubble-pile evolution, impact cratering physics, to the long-term effects of space weathering in the inner Solar System, Hera will have a major impact on many fields. Additionally, those studies using Hera data will in turn affect our understanding of the asteroid population as a whole. The scientific legacy of the Hera mission will extend far beyond the core aims of planetary defense. Acknowledgement: The authors acknowledge funding support from ESA and from the European Union's Horizon 2020 research and innovation programme under grant agreement No 870377 (project NEO-MAPP).