Hera: investigating the 'crime scene'

On 26 September 2022, NASA’s DART (Double Asteroid Redirection Test) collided with the 160-metre asteroid moon Dimorphos with a speed of 6.6 km per second. It was a test to see how effectively such a collision could change an asteroid’s orbit, should such a space rock approach Earth in the future.

Using terrestrial telescopes, we saw that a huge amount of material was flying out of the moon, and further observations showed that the 12-hour orbital period in which the moon orbits the larger asteroid Didymos was reduced by over half an hour. Test passed!

DART was obviously destroyed in this test, and the Italian nanosatellite that flew with DART had only a brief view of the impact as it skimmed past the asteroid at tremendous speed. From Earth, telescopes and radar systems cannot accurately map all the effects of the impact, and so many questions remain unanswered about the mass, composition, and internal structure of Dimorphos, as well as the shape of the crater caused. Therefore, ESA will send the Hera probe to the Didymos system in 2024. By the end of 2026, it should begin a more detailed investigation of the ‘crime scene’. Two CubeSat nanosatellites will also accompany Hera for additional observations: Milani will make spectral surface observations, while Juventas will carry out the first-ever radar probes inside an asteroid.

Hera is being built by OHB in Germany while other elements of the mission are taking shape across Europe. Hera’s precision guidance, navigation and control system, for example, essential to fly the spacecraft to and around its twin asteroid destination, is being developed by GMV in Spain.

Michel van Pelt from ESA ESTEC is involved in the Hera project and in his presentation will discuss the (long) history of the project, the importance of “planetary defence” against dangerous asteroids, the results of the DART impact, and Hera itself.