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Hera close flyby of Mars – The ROB took part in data analysis

14 Mar 25

Hera close flyby of Mars – The ROB took part in data analysis


On Mars 12 2025, at 13:51 (Belgian local time), the ESA Hera mission for planetary defence made a close flyby of the planet Mars and its moons Deimos and Phobos. Scientists took the opportunity to study Deimos, photograph Mars and Phobos and calibrate Hera instruments. Scientists from Royal Observatory of Belgium (ROB) take part in the data analysis of the Thermal Infrared Imager (TIRI) onboard Hera in collaboration with VITO Remote Sensing from Belgium and the Japanese Space Agency (JAXA).

A collage of four images of a red planet with a bright dot in the foreground.

Series of images of Deimos and the surface of Mars in the background taken by the TIRI camera on board Hera. False-colour image (composite colours), as the infrared is not visible to the naked eye. Credits: JAXA/TIRI, ESA/HERA, ROB.

Gravitational assist is a technique in which a spacecraft, during a close approach of a celestial body, uses its gravity to modify its velocity and accelerate. Such technique reduces fuel consumption and shortens the travel time of a spacecraft to its destination.

On March 12 2025, Hera passed over Mars from around 5000 km and over its moon Deimos as close as 300 km. Such close approach was an opportunity for scientists to study those celestial bodies, especially Deimos and its far side, which is rarely imaged. At the same time, instruments onboard Hera could be calibrated during this event to optimise their observation conditions for its mission at the asteroid Didymos system.

Image of a red planet with a bright dot in the foreground. Next to the image is a temperature scale with hot temperatures in yellow, cold temperatures in violet and red colours for mid temperatures.

Image of Deimos and the surface of Mars in the background with a scale showing the relative brightness temperature of the image zones. False-colour image (composite colours), as the infrared is not visible to the naked eye. Credits: JAXA/TIRI, ESA/HERA, ROB.

TIRI is the thermal infrared imager on-board the Hera spacecraft. The camera operates between 8 and 14 µm wavelengths which covers the peak of thermal emission from the expected range of temperatures of the targets of the mission. The flyby of Mars is an opportunity to calibrate the thermal camera with real flight measurements.

To receive and process TIRI data, Özgür Karatekin and Grégoire Henry came to the European Space Operations Centre (ESOC) in Darmstadt, Germany, while Luca Ruiz Lozano carried out radiometric calibration and analysis in Brussels. A selection of the best images was then presented during a press conference at ESOC on March 13 2025.

View of Deimos and the surface of Mars in the background taken by the TIRI camera on board Hera. Image with composite colours added. Images in false colour (composite colours), infrared not being visible to the naked eye.Credits: JAXA/TIRI, ESA/HERA, ROB.

Hera continues its journey to the Didymos system. It will then carry out a second deep space manoeuvre in February 2026 before a sequence of rendezvous manoeuvres from October to December 2026 brings it into proximity of the asteroids. There, Hera will begin to study the asteroids and the consequence of the DART impact on Dimorphos.  With the TIRI imager, we will have the opportunity to have new insights on the surface of Dimorphos and its properties and, ultimately, manage better the strategy to protect Earth from asteroids.

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