Light blue Mars and very small dark Deimos viewed by Hera's Hyperscout H
Mars and Deimos viewed by Hera's Hyperscout H ESA / ESA Standard Licence
On March 12, the European Space Agency’s (ESA) Hera spacecraft captured rare images of Deimos, one of Mars’ two moons, from 621 miles away while en route to the asteroid moonlet Dimorphos.
Like our moon, Deimos is tidally locked to Mars, meaning the same side always faces the planet—the only side visible to rovers on the Martian surface. The only way to see Deimos’ far side up close is for a probe like Hera to fly behind it, making such images more of a rarity.
“It’s one of the very few images we have of the far side of Deimos,” says Stephan Ulamec, a geophysicist at the German Aerospace Center and a member of the Hera team, as reported by the New York Times.
In the image below, Deimos, which is around 7.7 miles wide, appears as a dark object in front of the cratered Martian surface. Hera took this image with its black and white Asteroid Framing Camera, which photographs visible light. The Asteroid Framing Camera serves as both a navigation and scientific investigation tool.
black and white Mars and Deimos viewed by Hera's Asteroid Framing Camera
Mars and Deimos viewed by Hera's Asteroid Framing Camera
Hera captured the images while conducting a flyby, also known as a gravity assist: a maneuver that harnesses a planet’s gravity to accelerate and redirect a spacecraft, reducing the need for fuel and saving time and resources.
“It’s a series of breathtaking moments,” Paolo Martino, Hera’s lead engineer and deputy project manager, said of the spacecraft’s journey shortly before its launch in 2024, per the Guardian’s Ian Sample.
Six months later, the team “did a great job of planning the gravity assist,” ESA’s Hera spacecraft operations manager Caglayan Guerbuez says in a statement. “Especially as they were asked to fine-tune the maneuver to take Hera close to Deimos—which created quite some extra work for them.”
Hera also captured hyperspectral imaging using its Hyperscout H, which detects light across multiple wavelengths—including those beyond human vision—to help analyze the asteroid's mineral composition.
Though Dimorphos and the asteroid Didymos pose no threat to Earth, in 2022 NASA smacked a spacecraft into Dimorphos as part of its Double Asteroid Redirection Test (DART) mission testing the technique’s potential to redirect a future Earth-threatening asteroid. The mission was successful, making Dimorphos the first (and currently only) asteroid whose orbit was changed by humans. Hera’s aim is to further investigate the results of the DART mission in order to turn the approach into a repeatable technique.
“The more detail we can glean the better as it may be important for planning a future deflection mission should one be needed,” University of Maryland astronomer Derek Richardson told Associated Press’ Marcia Dunn in October.
The gif below is a sequence of images captured by Hera’s Thermal Infrared Imager, a Japan Aerospace Exploration Agency instrument that documents surface temperatures.
black and white gif, Deimos appears to cross Mars
Deimos appears to cross Mars ESA / JAXA / ESA Standard Licence
Hera is scheduled to reach the Didymos system in December 2026. It remains to be seen what further information the mission will glean from our crash site.