ESA’s Hera mission has captured images of asteroids (1126) Otero and (18805) Kellyday. Though distant and faint, the early observations serve as both a successful instrument test and a demonstration of agile spacecraft operations that could prove useful for planetary defence.
Hera is currently travelling through space on its way to a binary asteroid system. In 2022, NASA’s DART spacecraft impacted the asteroid Dimorphos, changing its orbit around the larger asteroid Didymos. Now, Hera is returning to the system to help turn asteroid deflection into a reliable technique for planetary defence.
Hera enters the asteroid belt
Hera launched from Earth on 7 October 2024 and flew past Mars in March 2025, where it used the planet’s gravity to alter its trajectory and align it for arrival at the Didymos binary asteroid system in late 2026.
On 11 May 2025, as Hera cruised through the main asteroid belt beyond the orbit of Mars, the spacecraft turned its attention toward Otero, a rare A-type asteroid discovered almost 100 years ago.
From a distance of approximately three million kilometres, Otero appeared as a moving point of light – easily mistaken for a star if not for its subtle motion across the background sky.
Hera captured images of Otero using its Asteroid Framing Camera – a navigational and scientific instrument that will be used to guide the spacecraft during its approach to Didymos next year. But this wasn’t just a sightseeing exercise.
Giacomo Moresco, Flight Dynamics Engineer at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, explains that the goal of the observations was to test the camera in conditions similar to those expected during Hera’s first sighting of Didymos.
“Didymos will also be a tiny, faint point of light among the stars when it first appears,” says Moresco. “The spacecraft will need to identify Didymos as soon as possible and keep the asteroid in the centre of the camera’s field of view as it approaches.”
An operational challenge
“The Hera spacecraft is performing very well,” notes Moresco. “So, we can use the cruise phase to test procedures and carry out other activities that will help us prepare for arrival, such as attempting to observe nearby asteroids.”
To carry out the observations, ESOC’s Flight Dynamics and Mission Analysis teams first compared Hera’s trajectory against those of hundreds of thousands of known asteroids. They found that Otero, thanks to its well-known orbit and relative brightness, was the best candidate.
It then took Hera’s Flight Dynamics and Flight Control teams just a couple of weeks to prepare and execute the necessary spacecraft slews and observation sequences – a feat of flexibility and technical execution for a deep space mission.
Hera tracked Otero for three hours, capturing one image every six minutes. By aligning the star fields across frames, the team was able to create a time-lapse that highlighted the asteroid’s relative motion.
