Back in 2022 on the 26 September, NASA’s DART mission successfully crashed into the asteroid Dimorphos. It was the first ever planetary defence test which demonstrated that a spacecraft could alter an asteroid’s orbit through kinetic impact alone, shortening Dimorphos’ orbit around its parent asteroid Didymos by 32 minutes. Now, the Hera spacecraft is on its way to Dimorphous to understand more about the impact of the DART mission.
Schematic of the DART mission shows the impact on the moonlet of asteroid (65803) Didymos. Post-impact observations from Earth-based optical telescopes and planetary radar would, in turn, measure the change in the moonlet’s orbit about the parent body (Credit : NASA/Johns Hopkins Applied Physics Lab)
Before it got there however, it’s used a gravitational slingshot from Mars to send it on its way. It’s a navigation technique that uses a body’s gravity to alter trajectory and speed and, in essence, when a spacecraft flies past it “borrows” some of the planet’s orbital energy, gaining velocity without using fuel. This technique has enabled missions like Voyager and New Horizons to reach distant targets that would otherwise require vast amounts of propellant, effectively using planets and moons as natural accelerators to efficiently navigate the Solar System.
Artist impression of the Voyager spacecraft heading out into interstellar space (Credit : NASA)
During its recent Mars gravity assist, travelling at 9 km/s, ESA’s Hera spacecraft captured images of the Martian moon Deimos from a distance of just 1000 km. It gave a rare glimpse of the side of the tidally locked moon that faces away from Mars. The origin of Deimos is still a mystery as the 12.4 km wide moon may be either debris from a massive Mars impact or a captured asteroid. ESA’s Mission Analysis and Flight Dynamics team at ESOC saw this as an opportunity to grab some useful scientific data while using Mars to adjust the spacecrafts path.
Hera was able to test three key instruments during the flyby: its 1020×1020 pixel Asteroid Framing Camera (for visible-light imaging and navigation,) the Hyperscout H Hyperspectral Imager (capturing 25 spectral bands beyond human vision to analyse mineral composition,) and JAXA’s Thermal Infrared Imager (to measure surface temperatures to analyse physical properties like roughness and porosity.) ESA’s Hera mission scientist Michael Kueppers noted that while these instruments were previously tested during Earth departure, this was a great opportunity first deployment on a small, distant, and poorly understood moon, successfully demonstrating their capabilities.
Colour version of the image using data from ESA’s Mars Express. A high resolution version can be downloaded here (Credit : Andrea Luck)
After this encounter, Hera is now en-route to its primary targets – the much smaller Didymos (780m) and Dimorphos (151m) asteroids. The spacecraft will undergo a trajectory correction manoeuvre in February 2026, followed by a series of thruster firings beginning in October 2026, to arrive at the Didymos system by December 2026.
Source : Hera asteroid mission spies Mars’ Deimos moon