On 12 March 2025 ESA’s Hera mission for planetary defence performs a flyby of Mars. Mars’s gravity will shift the spacecraft’s trajectory towards the Didymos binary asteroid system, shortening its trip by months and saving substantial fuel. This manoeuvre also marks the first time scientific use of Hera’s instruments, to image Deimos – the smaller and more enigmatic of Mars’s two moons.

1. Hera starts to see Mars about 10 days before closest approach, when the planet is 10 pixels across.
2. Hera comes to around 5000 km from the surface of Mars and 300 km from Deimos.
3. As Hera departs Mars it will also have a chance to image Mars’s other moon, Phobos.
4. Hera’s speed relative to Mars will be unchanged, but the spacecraft will swing around on course towards Didymos on a fuel-efficient basis.

Watch the star-studded webcast image release from Hera’s flyby by the mission’s science team on Thursday 13 March, starting at 11:50 CET!

Almost all ESA interplanetary missions make some use of the gravity fields of passing planets to gain velocity or change trajectory. These gravity assists are planned by ESA’s Flight Dynamics Team at ESOC in Germany and carried out by the Flight Control team. They are also visualised using SPICE (Spacecraft, Planet, Instrument, C-matrix, Events) software by a dedicated team at ESAC in Spain, to help plan image acquisitions.