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by Spektrum der Wissenschaft
Asteroid probe Hera on course for its destination
25.3.2026
Translation: machine translated
With the completion of its last major thrust manoeuvre, the European space probe Hera is now on a direct route to the double asteroid Didymos/Dimorphos. It will arrive there in November 2026 and explore it up close for an extended period of time.
In mid-March, the European Space Agency ESA carried out the last major thrust manoeuvre for its asteroid mission Hera. A total of 123 kilograms of hydrazine was used, a highly reactive fuel that is only used in special areas such as space travel due to its toxicity. Hera's speed thus changed by a whole 367 metres per second (1320 kilometres per hour). The probe is now on a direct course to its destination, the double asteroid Didymos/Dimorphos, which it is due to reach in November 2026. With the thrust manoeuvre, Hera also finally entered the plane of the asteroid pair's orbit around the sun, which is inclined 3.4 degrees to the Earth's orbit. In the coming weeks and months until its arrival, Hera will make several minor corrections to finalise its approach.
On arrival at the target area, a three-week approach phase will begin, during which the double asteroid will be detected using remote sensing instruments. Hera will then enter orbit in November - although this is more of a formation flight. The main body of Dimorphos is only around 780 metres in size, meaning that its gravitational field is practically negligible. Hera must therefore be actively steered in order to remain in the immediate vicinity. Both celestial bodies are rather loose accumulations of boulders and finer material. They are therefore also referred to as rubble piles.
Dimorphos, or Didymos, was already the target of the NASA space probe DART, which collided with the approximately 170-metre asteroid moon in September 2022. It orbits the main body at a distance of 1200 metres and takes around twelve hours to complete one orbit. The impact of DART left behind a crater, which Hera is now to investigate more closely. The collision also reduced Didymos' orbital period around Dimorphos by around 33 minutes. ESA wants to use Hera to find out how much Didymos was changed by the impact of the space probe. Two daughter probes, each about the size of a shoebox, are also to be deployed for this purpose, which can explore both celestial bodies simultaneously together with their mother probe. At a later date, it is planned that both will touch down gently on the surface of Didymos. Hera is scheduled to explore the double asteroid until at least June 2027, and an extension of the mission is entirely conceivable.
Didymos and Dimorphos orbit the sun in 2.11 years on a highly elliptical orbit with an eccentricity of e = 0.38. The average distance to the sun is 1.64 astronomical units, which is 1.64 times the distance from the Earth to the sun. The asteroid pair can approach us to a distance of around six million kilometres - this corresponds to around 16 times the distance between the Earth and the moon. Despite this comparatively small distance from a cosmic perspective, the two asteroids pose no danger to Earth for the next few centuries.
Spectrum of Science
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Header image: © NASA/Johns Hopkins APL / Dimorphos: High-Resolution Mosaic (detail)
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