While performing its flyby of Mars this week, ESA’s Hera mission made the first use of its payload for scientific purposes beyond the Earth and Moon. Activating a trio of instruments, Hera imaged the surface of the red planet as well as the face of Deimos, the smaller and more mysterious of Mars’s two moons.
Launched on October 7, 2024, Hera is on its way to visit the first asteroid to have had its orbit altered by human action. By gathering close-up data about the Dimorphos 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 March 12 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 5000 kilometres away from Mars, the planet’s gravity shifted the spacecraft’s trajectory towards its final destination, the Didymos binary asteroid. This manoeuvre shortened its journey time by many months and saved a substantial amount of fuel.
Moving at nine kilometres per second relative to Mars, Hera was able to image Deimos from as close as 1000 kilometres away, surveying the less-seen opposite side of the tidally locked moon from Mars. Measuring 12.4 kilometres across, dust-covered Deimos might be a leftover of a giant impact on Mars or else a captured asteroid.
“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 Caglavan Guerbuez. “Especially as they were asked to fine-tune the manoeuvre to take Hera close to Deimos, which created quite some extra work for them!”
Hera instruments were used during the flyby included:
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Hera’s black and white 1020 x 1020 Asteroid Framing Camera used for both navigation and scientific investigation acquires images in visible light;
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Hera’s Hyperscout H hyperspectral imager observes in a range of colours beyond the limits of the human eye in 25 visible and near-infrared spectral bands to help characterise mineral makeup;
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Hera’s Thermal Infrared Imager, supplied by the Japan Aerospace Exploration Agency images at the 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, with possibly interesting results,” said Hera Mission Scientist Michael Kueppers.
Hera also performed some joint observations of Deimos with ESA’s own Mars Express, which has been in orbit around the red planet for more than two decades.
Results from the Deimos close encounter should help guide operational planning the next year’s Martian Moons eXploration Mission, MMX, being led by the JAXA in collaboration with NASA, the French space agency CNES, the German Aerospace Center, and ESA. MMX will not only collect detailed measurements of both Martian moons but also land on Phobos to collect a sample and return it to Earth for analysis.
With Didymos being 780 metres across and Dimorphos just 151 metres across, Hera’s twin destinations are many times smaller than the city-sized Deimos moon, but Hera is headed on course towards them. A series of impulsive rendezvous thruster firings starting in October 2026 will fine-tune its heading to reach the Didymos system that December.
“This has been the Hera team’s first exciting experience of exploration, but not our last,” said Hera Mission Manager Ian Carnelli. “In 21 months the spacecraft will reach our target asteroids and start our crash site investigation of the only object in our Solar System to have had its orbit measurably altered by human action.”
