The European Space Agency's Hera mission has captured brand new images of Mars's moon Deimos while performing a close fly-by.
Hera, whose main mission is gathering information to help defend Earth from potentially dangerous space rocks, also captured images of the surface of Mars during the close pass.
And because Deimos is tidally locked to Mars – meaning the same side always faces the planet, just like Earth and its moon – Hera's images show the side of the moon not seen by rovers on the surface of the Red Planet.
The Hera spacecraft launched on 7 October 2024 and is making its way to visit asteroid Dimorphos, which was purposely impacted by NASA's DART spacecraft in 2022.
DART – the Double Asteroid Redirection Test – was a test to see whether humanity had the technological ability to knock off-course an asteroid heading for Earth.
This is something that recently came to be relevant given the initial worries surrounding asteroid 2024 YR4.
The DART mission was a success, the spacecraft smashing into the small moon of asteroid 65803 Didymos, as planned.
Telescopes on Earth measured the change in the moonlet’s orbit, and the Hera mission will study the damaged target up close in 2026.
Hera is tasked with gathering extra information on the aftermath of the DART mission to help scientists learn more about deflecting future, potentially dangerous asteroids.
Hera's Deimos flyby
Hera flew by Deimos on 12 March 2025, coming as close as 5,000 km to Mars.
This was a chance for Hera's science team on the ground to use the spacecraft's scientific instruments at a target beyond Earth and the Moon for the first time.
Hera's three instruments photographed the surface of Mars and Deimos, the smaller of the Red Planet's two moons.
The flyby was also a 'gravity assist', using Mars's gravitational pull to change the spacecraft’s trajectory towards its final destination, the Didymos binary asteroid.
Soaring past Mars at 9 km/s relative to the planet, Hera captured an image of Deimos as close as 1,000 km away.
It was able to survey the far side of the Martian moon, which is tidally locked to Mars.
This means that the same side of Deimos always faces the planet, and so this side is less-commonly seen.
Deimos measures 12.4 km wide and scientists think it could be a captured asteroid, or else a chunk taken out of Mars by a past impact on the planet.
"Our Mission Analysis and Flight Dynamics team at ESOC in Germany did a great job of planning the gravity assist," says ESA’s Hera Spacecraft Operations Manager Caglayan Guerbuez.
"Especially as they were asked to fine-tune the manoeuvre to take Hera close to Deimos – which created quite some extra work for them!"
Hera's science instruments
During the flyby, Hera used:
The black and white 1020x1020 Asteroid Framing Camera designed for navigation and science
The Hyperscout H hyperspectral imager that observes in a range of wavelengths beyond the limits of the human eye
The Thermal Infrared Imager that captures images at mid-infrared wavelengths
"These instruments have been tried out before, during Hera’s departure from Earth, but this is the first time that we have employed them on a small distant moon for which we still lack knowledge, with possibly interesting results," says ESA’s Hera mission scientist Michael Kueppers.
"Other Hera instruments we will utilise once we reach the Deimos and Dimorphos asteroids were not activated either because they are not usable at such long range and rapid speed from a target – such as our PALT laser altimeter, possessing a maximum range of 20 km – or because they are aboard Hera’s pair of CubeSats which will only be deployed at the asteroids," says Hera Principal Investigator Patrick Michel, Director of Research at CNRS / Observatoire de la Côte d'Azur.
Scientists say the results from Hera's Deimos flyby will also help plan the Martian Moons eXploration Mission, MMX, which will study both Mars moons, Phobos and Deimos, and land on Phobos to return a sample of it for study back on Earth.
