In one month, the European Space Agency’s Hera mission will make history. Moving at 12 kilometers per second relative to Earth, the mission is about to rendezvous with the binary Dimorphos-Didymos asteroid pair. NASA’s Double Asteroid Redirection Test (DART) mission slammed into Dimorphos in 2022, and now Hera will provide a follow-up view of the mission’s resulting handiwork. The European Space Agency (ESA) recently released a thought-provoking look at the perspectives of Hera, and what an astronaut might see from the surface of the asteroids as the mission speeds by.
But what would it be like to hitch a ride aboard Hera? Launched on a SpaceX Falcon-9 rocket from Cape Canaveral, Fla. on 7 October 2024, Hera is ESA’s first Space Safety Programme-class mission. The spacecraft took just over two years to reach its destination. Even now, the pair of asteroids is little more than a few pixels across in Hera’s view. The mission imaged Didymos in July 2026.
Why Hera is chasing Didymos
Discovered by the Kitt Peak Spacewatch survey on 11 April 1996, 65803 Didymos is 780 meters in diameter, and it orbits the Sun once every 2.1 years. In 2003, the asteroid was discovered to have a small moonlet, a 151-m rock named Dimorphos. Scientists are finding that more and more asteroids are in fact binary pairs in their own right.
Like our Moon, the pair are dark and silicon-rich. The meetup with Hera also occurs 1.5 astronomical units from the Sun. This makes for a dimmer view, though it still provides enough juice for Hera’s two 5-m long solar panels.
Didymos is a fast rotator, spinning once every 2.2 hours. DART saw Dimorphos as a ‘rubble pile asteroid’ shortly before impact, similar to 101955 Bennu or 162173 Ryugu, visited by NASA’s Osiris-REX and JAXA’s Hayabusa-2 missions respectively. These rock piles are thought to be at their limits in terms of holding together versus flying apart. DART’s 6.6 km/s impact did shorten the original 11 hour, 55 minute orbit by about 32 minutes, and a debris stream was seen from the binary pair in the weeks after impact.
An arrival preview should provide the first close up views of Dimorphos post-impact. This sort of study could prove handy, if we ever need to move an Earthbound asteroid out of harm’s way.
Certainly, standing on the boulder strewn surface of either asteroid would provide an alien vista of a spinning sky dominated by the other nearby asteroid companion. The feeble gravitational pull of either asteroid would allow a would-be astronaut to fall to the surface of either at a days-long leisurely rate.
Hera’s pair of CubeSats will put that to the test. Juventas and Milani—built by GomSpace, in Luxembourg, and Tyvak International, in Turin, Italy, respectively—will leave Hera shortly after rendezvous next month. Milani will analyze the dust field around both asteroids and study the spectral composition of the pair, while Juventas will make comparisons of the internal structure of the asteroids and may even approach and come to rest on Dimorphos.
After Hera is done with its nominal mission in 2027, controllers may opt to extend its life as a technology demonstrator, testing autonomous spacecraft control techniques.
It’s going to be exciting to get a look at the Didymos-Dimorphos system again. And although we can’t be there in person, we can still get a close look at these alien worlds through Hera’s eyes.
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