The ESA Hera Mission: Investigating binary asteroid (65803) Didymos and the DART crater

One week ahead of the impact by NASA’s Double Asteroid Redirection Test (DART) spacecraft with Dimorphos, the moon of binary asteroid (65803) Didymos, representatives of the European Space Agency’s Hera mission, the Italian LICIACube mission and DART have presented an update on the missions at the Europlanet Science Congress (EPSC) 2022.

Planetary defense is the preparation of humankind to avoid a catastrophic collision between Earth and asteroids, like the Chicxulub event that led to the extinction of the dinosaurs 65 million years ago, or the impact of an asteroid that created the 1km-size meteor crater in Arizona about 50 000 years ago. Humanity’s first ever demonstration of asteroid deflection is happening right now: On 26 September 2022, NASA’s Double Asteroid Redirection Test (DART) spacecraft will impact the asteroid Dimorphos—which poses no threat to Earth—to change its orbit in a measurable way. The Johns Hopkins Applied Physics Laboratory (APL) manages the DART mission for NASA’s Planetary Defense Coordination Office as a project of the agency’s Planetary Missions Program Office. Using the same technique, humankind could in the future attempt to deviate an asteroid on collision course with Earth if a threat were ever discovered.

Dimorphos is part of an asteroid pair, like the Earth-Moon system, and orbits around a larger asteroid called Didymos. Following DART’s impact, the change in Dimorphos’ orbit can be detected by telescopic observations from Earth, and during a few minutes following the impact, observations of the ejecta from the impact will be attempted by LICIACube, a small briefcase-sized satellite travelling along with DART and contributed by the Italian Space Agency (ASI). Therefore, shortly after the impact, we should know whether DART hit successfully Dimorphos as well as the geological properties of the impact site, whether ejecta have been produced by the impact and we will have a quantification of the resulting orbital change of the target around its central body Didymos. 

However, to further understanding of the impact process and the scaling of the outcome to other asteroids, a follow on investigation of the target asteroid and the crater resulting from DART’s kinetic impact are planned. This detailed investigation will be performed by ESA’s Hera mission. To be launched in 2024, Hera will rendezvous with the Didymos system in late 2026. Together with its two companion “cubesats”, called Juventas and Milani, the mission will perform a full characterization of the deflection measuring the mass of Dimorphos to help further understand the efficiency of the DART impact, as well as studying the impact crater in detail. Additionally, Hera aims to further improve understanding of the kinetic spacecraft impactor process and investigate the physical properties of the target asteroid. This will help enable scaling the impact outcome to other targets.

Integration of the Hera spacecraft and its scientific instruments are ongoing. Together with DART, this pair of missions will not only validate the kinetic impactor asteroid deflection technique but also provide unique clues on the formation processes of binary asteroids and ultimately of the Solar System.