Hera Arrives at the Didymos Binary Asteroid System to Inspect DART Wreckage
Four years after NASA’s DART spacecraft intentionally collided with the asteroid Dimorphos in history’s first planetary defense test, the European Space Agency’s Hera probe arrives this month to inspect the wreckage, as reported by Space. Launched on October 7, 2024, the small-car-sized spacecraft is executing precise braking maneuvers to rendezvous with the binary system and evaluate the structural consequences of the high-speed impact.
Executing Deep Space Braking Maneuvers Near Didymos
The journey to the binary system required a two-year transit, punctuated by deep space maneuvers and a Mars flyby in the spring of 2025 to adjust trajectory and velocity. Moving at a relative speed exceeding 12 kilometers per second, the mission faces its most critical operational phase yet. According to the European Space Agency, mission controllers initiated a sustained 93-minute triple-thruster burn using hydrazine-based propulsion to reduce the spacecraft’s velocity.
🛰️I'm currently speeding my way thru deep space to the Dimorphos🪨asteroid, the only Solar System body whose orbit has been shifted by human action – when NASA's DART spacecraft💥impacted it – to check what happened to it next! See where I am right now: https://t.co/FWLbLzMAU0 pic.twitter.com/A3j2kIQRkE
A second braking maneuver, designated BRM-2, is scheduled for implementation on October 22, compensating for minor performance variances and matching the velocity of the Didymos system. Three smaller transition maneuvers later in the month will drive the relative velocity down near zero, setting the stage for close-range observations.
By early November, Hera will position itself within 20 miles of the two space rocks to begin early science operations, moving even closer by December.
Unresolved Questions Surrounding the Dimorphos Impact
While ground-based and space telescopes calculated that the 2022 collision shortened Dimorphos’s orbit around the larger asteroid Didymos by roughly 33 minutes, significant mysteries remain. Researchers note that the orbital period continued shifting for six months after impact in ways that defy simple models. Scientists do not yet know the exact dimensions of the crater left behind, whether the impact completely rearranged surface boulders, or if material migrated between Dimorphos and Didymos. Furthermore, observations suggest Dimorphos may now be tumbling.
Discovered by the Kitt Peak Spacewatch survey on April 11, 1996, the primary asteroid Didymos spans 780 meters in diameter, while its smaller moonlet Dimorphos measures 151 meters. Both bodies are dark, silicon-rich rubble piles similar to asteroids Bennu and Ryugu. Universe Today notes that DART struck Dimorphos at 6.6 kilometers per second, creating a debris stream visible to space telescopes for weeks following the event.
Deploying Companion Probes for Subsurface Radar Analysis
Once Hera stabilizes its position in early 2027, the primary spacecraft will release two piggybacked companion probes to examine the binary system up close. The Milani companion will map surface mineral compositions, while the Juventas probe will deploy low-frequency radar to peer directly inside Dimorphos—marking the first time humanity has studied the interior of an asteroid. Both miniature craft will conclude their mission segments by attempting landings on the asteroid.
The primary Hera spacecraft will continue operations through at least September 2027, gathering unprecedented data on the first binary asteroid ever visited in detail.
