Hera flies over Deimos on its way to Dimorphos : a major step forward for planetary protection
On 12 March 2025, the European Space Agency's (ESA) Hera probe flew past Mars and its natural satellite Deimos. The aim of this crucial manoeuvre was to exploit the gravitational attraction of the Red Planet to adjust the probe's trajectory towards its main target: the Didymos-Dimorphos asteroid binary system, which it will reach in December 2026.
Mars and Deimos viewed by Hera / @ESA
Publication date: 13/03/2025
Events, General public, Press, Research
An unprecedented scientific opportunity: exploring Deimos
This flyby is a unique opportunity to study Deimos, whose origin is unknown. Thanks to the instruments on board Hera, valuable data on the composition and structure of the planet will be collected during the flyby. By observing Deimos up close, Hera could help determine whether this Martian moon is a captured asteroid or the remnant of an ancient impact. This stage of the mission could enrich our understanding of the formation of Martian moons and the evolution of the solar system.
In addition, these observations will provide essential information for future missions to Mars and its moons, in particular for the Japanese MMX mission (Mars Moon eXploration, JAXA), which will explore Phobos in 2028. All this research will help to clarify the interactions between small celestial bodies and their planetary environment.
The HERA mission will then continue its journey towards the Didymos-Dimorphos pair, which it will reach in 2026.
A key European mission for planetary defence
Hera aims to analyse in detail the consequences of the impact of NASA’s DART (Double Asteroid Redirection Test) mission, which collided with Dimorphos in 2022 to test asteroid deflection as a planetary defence strategy. The European mission will assess the changes brought about by this collision, refining our ability to protect the Earth against possible threats from space.
Unlike DART, which was a technological demonstration, Hera will provide a detailed analysis of Dimorphos’ post-impact properties. It will precisely measure its internal structure, composition and the effects of the collision, providing essential information for the future design of planetary defence strategies. This mission marks a major step forward for ESA, establishing Europe as a key player in protecting our planet from potentially dangerous asteroids. It will be the first European mission entirely dedicated to protecting the Earth from these cosmic threats, underlining ESA’s commitment to developing planetary defence strategies.
The in-depth study of Dimorphos will improve our understanding of the dynamics of small celestial bodies and their physical properties. By determining precisely how an impact can modify the trajectory and structure of an asteroid, Hera will lay the foundations for a rigorous scientific approach to anticipating and countering any asteroids that threaten the Earth. The impact of an asteroid around 70 million years ago is widely considered to be the main cause of the extinction of the dinosaurs.
The IPGP at the heart of the Hera mission
The Institut de Physique du Globe de Paris (IPGP) is playing a key role in the Hera mission through the work of Professor Sébastien Charnoz, a member of the CAGE (Cosmochemistry, Astrophysics and Experimental Geophysics) team. As a scientific member of the mission and head of the ‘Dynamics’ working group, he is contributing to the analysis of gravitational interactions and the dynamics of the Didymos-Dimorphos system. He is also involved in the Japanese MMX (Martian Moons eXploration) mission, scheduled for 2028, which will aim to explore Phobos, Mars’ other moon, in detail.
