European spacecraft got rare close-up of Mars’ lesser-known moon

A European spacecraft on a journey to study NASA‘s asteroid crash site did a quick pop-in of Mars on its way, capturing unprecedented images of Mars‘ lesser-known moon, Deimos. 

Mars has two moons, Phobos and Deimos, but scientists know relatively little about them, especially the smaller one, Deimos. Nearly all of the images they have of it were taken from the Martian surface by rovers, and because the moon is tidally locked — meaning one full spin matches the amount of time it takes to complete its orbit of Mars — only one side has been seen on the Red Planet. 

The Hera mission spacecraft captured views of the moon’s far side, swinging within 625 miles of Deimos in space. 

While the car-sized spacecraft flew around the Mars system, flight controllers on Earth temporarily lost communication with Hera because the signal was blocked. Though the blackout was planned for the maneuver, Ian Carnelli, the European Space Agency’s Hera mission manager, said it was deeply emotional. 

“I was almost in tears. I mean, I know probably this is normal for a flight for spacecraft operators, but every time we lose contact with a spacecraft, I’m super nervous,” he said during a webcast following the flyby. “Then I was running to the room where the scientists were [watching for images], and as soon as I opened the door, they were screaming — really screaming.”

Among those scientists was one of the co-founders of Queen. When Brian May isn’t playing guitar riffs, he is an astrophysicist. As part of Hera’s science team, May brings his expertise in stereoscopic imaging. That means he helps decipher complex scientific data into 3D pictures. 

During a webcast on Thursday, May described some of the topographical details of the moon already brought to life through the raw data. A depression in the city-sized moon was visible, a feature May described as a “saddle” on the left side and some little craters at the bottom. 

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“You feel like you’re there, and you see the whole scene in front of you,” he said. “The science that we get from this is colossal, and I think we’re all like children.”

Hera launched in October 2024 and will rendezvous with Dimorphos, an asteroid previously slammed by a NASA spacecraft, in 2026. Back in 2022, NASA deliberately crashed a spacecraft into a harmless asteroid to practice thwarting a space rock, should a hazardous one ever be on a collision course with Earth. The European Space Agency is providing a follow-up to that test.

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The flyby of Mars and Deimos wasn’t a detour but a necessary maneuver to put the spacecraft on the right trajectory toward its ultimate destination. Swinging within 3,100 miles of Mars, Hera used its gravity to adjust its course. 

Scientists would like to understand where Deimos and its partner Phobos came from — whether they were once asteroids captured in orbit around Mars or are chunks of the planet itself, blown out by a giant impact. 

The new data may help them figure out the moon’s origin. During the flyby, three instruments were used: a black-and-white navigation camera that takes pictures in visible light; a hyperspectral imager that can help discern an object’s mineral composition; and a thermal infrared imager supplied by the Japanese space agency, JAXA, which can help characterize the texture and density of the material. Overall, thousands of images were collected, and the Hera team is still processing them. 

At the top of this story is an infrared photo of Deimos, backdropped by Mars. The Red Planet appears pale blue because the sun is shining on it. Its contribution to this scene would need to be removed for the colors to appear closer to how they would really look to our eyes.

Near the top of the image is the bright Terra Sabaea region, close to the Martian equator. At the bottom right of the region is the Huygen crater, and to its left is the Schiaparelli crater. At the bottom right of the planet is Hellas Basin, one of the largest known craters in the solar system. 

In a little less than two years, Hera will reach the target asteroids from NASA’s DART mission to begin a crash investigation.