On March 12, 2025, Hera — ESA’s first Space Safety mission — came to within 5,000 km of the surface of Mars and 1,000 km of Deimos. While performing the flyby, the spacecraft made the first use of its payload for scientific purposes beyond Earth and the Moon. Activating a trio of instruments, Hera imaged the Martian surface as well as the face of Deimos.
Mars appears light blue in this near-infrared image from Hera’s Hyperscout H hyperspectral imager, acquired during the mission’s March 12 gravity-assist flyby of Mars, with Deimos seen ahead of it. The spacecraft was approximately 1,000 km from the 12.4-km-diameter Deimos when this image was acquired. In the background a variety of Martian features can be observed. At the top of the image is the bright Terra Sabaea region, close to the Martian equator, outlined by darker regions about it, with the 450 km-diameter Huygen crater to the bottom right of Terra Sabaea and the 460-km-diameter Schiaparelli crater to its left. To the bottom right of the Martian disk is Hellas Basin, among the largest known impact craters in the Solar System with a diameter of 2,300 km and a depth of more than 7 km. Image credit: ESA.
Launched on October 7, 2024, Hera is on its way to visit Dimorphos, the first asteroid to have had its orbit altered by human action.
By gathering close-up data about this asteroid, which was impacted by NASA’s DART spacecraft in 2022, Hera will help turn asteroid deflection into a well understood and potentially repeatable technique.
Hera’s flyby of Mars was an integral part of its cruise phase through deep space, carefully designed by ESA’s Flight Dynamics team.
By coming as close as 5,000 km away from Mars, the planet’s gravity shifted the spacecraft’s trajectory towards its target.
Moving at 9 km/s relative to Mars, Hera was able to image Deimos from as close as 1,000 km away, surveying the less-seen opposite side of the tidally locked moon from the red planet.
“Our Mission Analysis and Flight Dynamics team at ESOC in Germany did a great job of planning the gravity assist,” said ESA’s Hera spacecraft operations manager Caglayan Guerbuez.
“Especially as they were asked to fine-tune the maneuver to take Hera close to Deimos — which created quite some extra work for them!”
Three Hera instruments were used during the flyby:
– Hera’s Asteroid Framing Camera, used for both navigation and scientific investigation, acquires images in visible light;
– Hera’s Hyperscout H hyperspectral imager observes in a range of colors beyond the limits of the human eye, in 25 visible and near-infrared spectral bands, to help characterize mineral makeup;
– Hera’s Thermal Infrared Imager, supplied by the Japan Aerospace Exploration Agency (JAXA), images at mid-infrared wavelengths to chart surface temperature, in the process revealing physical properties such as roughness, particle size distribution and porosity.
“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 — demonstrating their excellent performance in the process,” said ESA’s Hera mission scientist Michael Kueppers.
“Other Hera instruments we will utilize 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 hosted aboard Hera’s pair of CubeSats which will only be deployed at the asteroids,” said Hera principal investigator Patrick Michel, director of research at Observatoire de la Côte d’Azur, CNRS.
