Hera glides past Didymos. © ESA

Why are DART and Hera playing billiards in space?

Well over 900,000 asteroids have already been discovered in our solar system. Of these, a good 1,000 are on the European Space Agency's (ESA) risk list due to their trajectory and size and are under special observation. However, ESA and other space agencies do not only observe these asteroids: they also develop models and missions that could prevent serious or even fatal asteroid impacts on Earth in the future.

AIDA: The first asteroid deflection demonstrator collaboration

One asteroid defence collaboration that ESA and NASA are currently working on together is AIDA (Asteroid Impact and Deflection Assessment). The collaboration consists of two parts: Part 1 is the NASA-contributed impact probe DART (Double Asteroid Redirection Test), Part 2 is the ESA observation probe Hera. Like in a game of billiards, DART is supposed to fly to an asteroid, collide with it and thereby change its path. The task of the Hera probe is then to analyse the effects of DART's impact.

DART is currently already on its way to the near-Earth double asteroid Didymos and will collide with Dimorphos, the smaller of the two bodies, in October 2022. The Hera probe is currently being built at OHB and will follow in 2024. Hera is scheduled to arrive at the Didymos system in 2026. Then it will become clear whether the impact of DART has had any effect on the orbit of Dimorphos. If so, this will lay the foundation for a practically applicable planetary defence strategy.