The European Space Agency’s (ESA) Hera mission, designed for planetary defense, has achieved a major milestone during its journey through deep space. In a historic first, the spacecraft activated its suite of scientific instruments beyond the Earth-Moon system, capturing images of Mars and its lesser-known moon, Deimos, during a close flyby on March 12.
Martian moon Deimos appears dark, framed by the brighter planet Mars behind it, in this visible light monochromatic Asteroid Framing Camera image, acquired by ESA's Hera spacecraft during its gravity-assist flyby on 12 March 2025.
Hera, launched on October 7, 2024, is en route to study Dimorphos—the asteroid whose trajectory was deliberately altered by NASA’s DART mission in 2022. By closely analyzing the asteroid, Hera aims to refine techniques for deflecting hazardous space objects, strengthening planetary defense efforts.
The flyby was a carefully orchestrated maneuver, planned by ESA’s Flight Dynamics team. Passing just 5,000 km from Mars, Hera used the planet’s gravity to adjust its trajectory toward its final destination, Dimorphos, and its larger companion, Didymos. This strategic move significantly reduced travel time and conserved fuel for the remainder of the mission.
During the flyby, Hera reached speeds of 9 km/s relative to Mars and observed Deimos from just 1,000 km away. The spacecraft successfully imaged the far side of the Martian moon—an area rarely seen, even from Mars itself. Deimos, measuring 12.4 km in diameter, is believed to be either a remnant from a massive impact on Mars or a captured asteroid.
ESA’s Hera Spacecraft Operations Manager, Caglayan Guerbuez, praised the precision of the maneuver: “Our Mission Analysis and Flight Dynamics team at ESOC in Germany executed the gravity assist flawlessly. They even fine-tuned Hera’s trajectory to ensure a close pass by Deimos, demonstrating remarkable accuracy.”
Scientific Breakthroughs from Hera’s Instruments
Three of Hera’s onboard instruments were activated during the flyby:
Asteroid Framing Camera – A high-resolution black-and-white imager that captured visible-light images to support navigation and scientific analysis.
Hyperscout H Hyperspectral Imager – A sophisticated sensor that analyzed Deimos in 25 spectral bands, helping scientists determine its mineral composition.
Thermal Infrared Imager – Provided by JAXA, this instrument mapped surface temperatures, offering insights into Deimos’ roughness, particle size, and porosity.
“This was the first real deployment of Hera’s scientific payload on a distant celestial body, and the instruments performed beyond expectations,” said ESA’s Hera mission scientist Michael Kueppers.
Other advanced tools, such as Hera’s PALT laser altimeter, remained inactive due to the spacecraft’s high velocity and distance. Meanwhile, Hera’s CubeSats will only be deployed once the spacecraft reaches Dimorphos.
Hera also collaborated with ESA’s long-operating Mars Express orbiter to conduct joint observations of Deimos. The data gathered will contribute to future missions, particularly JAXA’s upcoming Martian Moons eXploration (MMX) mission, which aims to analyze Mars’ moons and return a sample from Phobos to Earth.
The Road Ahead: Dimorphos Mission in 2026
While Deimos is significantly larger than Hera’s primary targets—Dimorphos (151 m wide) and Didymos (780 m wide)—the successful flyby confirmed the spacecraft’s precise trajectory. A planned course correction in February 2026, followed by a series of carefully timed maneuvers, will ensure Hera reaches the Didymos system in December 2026.
“This marks the first of many thrilling exploration phases for Hera,” said ESA’s Hera mission manager, Ian Carnelli. “In just 21 months, we will arrive at our target asteroids and begin a detailed study of the only celestial body in the Solar System whose orbit has been altered by human intervention.”
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