In one month, the European Space Agency’s Hera mission will rendezvous with the binary Dimorphos-Didymos asteroid pair, providing the first close-up views of an asteroid after NASA’s Double Asteroid Redirection Test (DART) deliberately struck it in 2022.
Launched on a SpaceX Falcon 9 rocket from Cape Canaveral on October 7, 2024, Hera took just over two years to reach its destination. The spacecraft is moving at 12 kilometers per second relative to Earth as it approaches the asteroids, which currently appear as only a few pixels in Hera’s view. According to the IEEE Spectrum report, Hera imaged Didymos in July 2026.
Didymos, discovered by the Kitt Peak Spacewatch survey on April 11, 1996, is 780 meters in diameter and orbits the Sun once every 2.1 years. The asteroid has a small moonlet named Dimorphos, a 151-meter rock discovered in 2003. Both asteroids are dark and silicon-rich, similar to other rubble pile asteroids previously visited by space missions.
DART’s impact on Dimorphos in 2022 was significant: the 6.6 km/s collision shortened the moon’s original 11 hour, 55 minute orbit by about 32 minutes, and a debris stream was observed in the weeks following impact. Didymos itself is a fast rotator, spinning once every 2.2 hours.
Hera, classified as ESA’s first Space Safety Programme-class mission, will deploy two CubeSats shortly after rendezvous. Milani will analyze the dust field around both asteroids and study their spectral composition, while Juventas will examine the internal structure and may even attempt to land on Dimorphos. The rendezvous occurs 1.5 astronomical units from the Sun, providing enough sunlight for Hera’s two 5-meter solar panels to function.
After completing its nominal mission in 2027, controllers may extend Hera’s operational life to test autonomous spacecraft control techniques. The mission represents a significant step in planetary defense research, demonstrating how humanity might redirect an Earth-bound asteroid if one ever posed a threat.
Key facts
- Hera will rendezvous with the Dimorphos-Didymos asteroid pair in one month, about four years after DART struck Dimorphos in 2022
- Didymos is 780 meters in diameter; its moonlet Dimorphos measures 151 meters
- DART’s impact shortened Dimorphos’s orbit by approximately 32 minutes
- Two CubeSats, Milani and Juventas, will separate from Hera to conduct detailed scientific analysis of the asteroid pair