Hera Probe Zips Past Mars, Snaps Photos of Deimos on Asteroid-Bound Journey

The European Space Agency’s (ESA) Hera spacecraft, en route to its asteroid rendezvous, executed a crucial maneuver around Mars, leveraging the Red Planet’s gravitational field to slingshot itself toward its ultimate destination. During this brief but significant interaction with Mars, Hera had the opportunity to test its scientific instruments, capturing images of the lesser-seen side of Deimos, one of Mars’ two moons. Deimos, tidally locked to Mars, always presents the same face to the planet, making Hera’s glimpse particularly valuable.

Launched on October 7, 2024, Hera is on a mission to meticulously analyze the aftermath of NASA’s Double Asteroid Redirection Test (DART) mission. DART intentionally impacted an asteroid to alter its orbit, a pioneering experiment in planetary defense. Hera’s role is to provide a comprehensive post-impact assessment, gathering data that ground-based telescopes alone cannot provide. While its primary objective lies in the asteroid belt, the Mars flyby served as a valuable opportunity to calibrate instruments and gather preliminary scientific data. Hera is slated to arrive at its asteroid target in 2026.

The spacecraft approached within 3,106 miles (5,000 kilometers) of Mars, close enough for the planet’s gravitational pull to effectively bend Hera’s trajectory towards its target binary asteroid system. During the flyby, Hera activated a suite of three scientific instruments, including imaging systems, to observe the Martian surface and, more importantly, its diminutive moon, Deimos. This was a crucial shakedown cruise for these instruments in deep space.

“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!” exclaimed Michael Kueppers, ESA’s Hera mission scientist, emphasizing the success of the instrument testing.

Mars is accompanied by two moons, Phobos and Deimos. Deimos, the smaller of the two, is a mere 7.7 miles (12.4 km) in diameter. Its origins remain somewhat mysterious; it could be a fragment that broke off from Mars following a massive impact, or it could be a captured asteroid ensnared by Mars’ gravity. Deimos completes one orbit around Mars in approximately 30 hours.

In addition to obtaining images of the irregularly shaped moon, Hera conducted joint observations of Deimos in coordination with ESA’s Mars Express orbiter. Mars Express has been orbiting Mars for over two decades, providing invaluable data on the planet and its environment, and this collaborative observation further enhanced the scientific return of the Hera flyby.

Hera’s ultimate destination is a binary asteroid system consisting of two asteroids: Dimorphos and Didymos. Dimorphos, the target of NASA’s DART mission, is a relatively small space rock measuring approximately 558 feet (170 meters) in width. It orbits Didymos, a much larger asteroid with a diameter of about 2,625 feet (800 meters).

In September 2022, NASA’s DART spacecraft, weighing 1,340 pounds, intentionally collided with Dimorphos in a groundbreaking test of planetary defense strategies. The impact was designed to slightly alter Dimorphos’ orbit around Didymos, demonstrating the feasibility of using kinetic impactors to deflect potentially hazardous asteroids away from Earth. The DART mission was deemed a resounding success.

Data collected by ground-based optical and radio telescopes revealed that the collision successfully altered Dimorphos’ orbital period. Prior to the impact, Dimorphos took 11 hours and 55 minutes to orbit Didymos. Following the collision, this orbital period decreased to 11 hours and 23 minutes, a measurable change demonstrating the effectiveness of the kinetic impactor technique.

However, ground-based observations alone provide only a partial picture of the impact’s consequences. Detailed measurements of the impact crater, the asteroid’s internal structure, and the overall dynamics of the binary system require a closer inspection from space. That is where Hera enters the picture.

Hera is tasked with performing a detailed, post-impact survey of the Dimorphos-Didymos system from orbit. The spacecraft will meticulously map the impact crater, analyze the asteroid’s surface composition, and measure its mass and internal structure. These data will provide valuable insights into the physics of asteroid impacts and the effectiveness of the DART mission.

The Hera mission is scheduled to perform a follow-up maneuver in February 2026. Subsequently, a series of thruster firings will commence in October 2026 to precisely adjust its trajectory for arrival at the Didymos system in December 2026. This careful navigation ensures that Hera arrives at the asteroid system at the optimal time and location for its scientific investigations.

“This has been the Hera team’s first exciting experience of exploration, but not our last,” stated Ian Carnelli, ESA Hera mission manager. “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.” This emphasizes the unique and historic nature of the Hera mission and its contribution to our understanding of planetary defense and the dynamics of the solar system. The detailed analysis Hera will provide is crucial for validating our models of asteroid impacts and improving our ability to protect Earth from future asteroid threats. The Hera mission represents a significant step forward in our efforts to understand and mitigate the risks posed by near-Earth objects.