ESA’s Hera is set to provide some spectacular new views of a familiar binary asteroid.
In just one more month, the European Space Agency’s Hera mission will make history. Moving at 12 kilometers per second versus 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.
Didymos (lower left) and Dimorphos, imaged by the DART spacecraft, shortly before impact. Credit: NASA
But what would it be like to ‘hitch a ride’ aboard Hera? Launched on a SpaceX Falcon-9 rocket from Cape Canaveral on October 7th, 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 is little more than a few pixels across in Hera’s view. The mission just imaged Didymos in July 2026.
Hera catches first sight of its binary asteroid destination. Credit: ESA.
Discovered by the Kitt Peak Spacewatch survey on April 11th, 1996, 65803 Didymos is 780-meters in diameter, and orbits the Sun once every 2.1 years. The asteroid was discovered to have a small moonlet in 2003, a 151-meter rock named Dimorphos. We’re 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-meter 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 must be at their limits in terms of holding together versus flying apart. DART’s 6.6 kilometer per second impact did change the original 11 hour 55 minute orbit down by about 32 minutes, and a debris stream was seen from the binary pair in the weeks after impact.
Hubble spies a debris stream from the asteroid pair, post-DART impact. Credit: NASA/HST/STScI.
An arrival preview should give us our 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.
DART's impact footprint across the surface of Dimorphos. Credit: NASA.
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 CubeSats will put that to the test. The pair, named Juventas and Milani were built by GomSpace Luxembourg and Tyvak International based in Turin, Italy respectively, and 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.
The Future of the Mission
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.
Hera images Deimos during the mission's March 2025 Mars flyby. Credit: ESA/Andrea Luck/CC BY 2.0
It’s going to be exciting getting 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.