The European Space Agency’s Hera spacecraft is arriving at the binary asteroid system of Didymos and Dimorphos to conduct a detailed post-impact survey following NASA’s DART mission, which collided with the smaller space rock.
Ground-based measurements still carry an estimated 10% residual uncertainty, and existing models have been unable to calculate the exact mass and makeup of Dimorphos, according to the European Space Agency. Hera aims to measure the asteroid’s mass and shifted orbit with higher accuracy while conducting the survey of a binary asteroid system, which accounts for roughly 15% of all known asteroids.
The spacecraft performed a braking maneuver on October 15, firing its thrusters to match the velocity of the asteroid pair after launching on October 7, 2024. The mission follows the September 26, 2022, DART test, which intentionally slammed a 1,340-pound spacecraft into the 558-foot-wide Dimorphos to alter its orbit around the 2,625-foot-wide Didymos.
Launched on October 7, 2024, by a Falcon 9 rocket from Florida, Hera performed a Mars flyby in March 2025 and passed approximately 300 kilometers from Mars’s small moon Deimos. Earlier in October, the spacecraft captured its first view of the Didymos binary asteroid system from an approximate distance of 146,954 miles (236,500 kilometers) away.
Following this initial observation, Hera executed a braking maneuver on October 15, operating its engines for 93 minutes to fine-tune its trajectory and nearly match the velocity of the two space rocks. The spacecraft is designed to come within 20 miles (30 kilometers) of the asteroids to begin gathering data.
🚨🚨🚨On its second birthday in space, ESA's Hera mission for planetary defence has spotted its asteroid destination for the first time, from an approximate distance of 236 500 km away! The Didymos system is actually two asteroids, seen as a single pixel for now… pic.twitter.com/jYl1eHdDtI
Measuring The DART Impact on Dimorphos
While ground-based observations confirmed that the collision shortened Dimorphos’s orbital period from 11 hours and 55 minutes to 11 hours and 23 minutes—a reduction of about 33 minutes—scientists require closer measurements to determine the physical consequences of the strike.
Patrick Michel, the scientific lead for the mission, outlined the objectives of the survey:
Did the impact produce a crater? And if so, what are its size and depth? Or did it entirely deform the asteroid?
Patrick Michel, scientific lead for the Hera mission
Hera Deploys Cubesats to Map and Land on Asteroids
After entering the system and coming within 20 miles of the asteroids, Hera will spend at least six months surveying the binary system. Hera will deploy a pair of shoebox-sized cubesats named Milani and Juventas. Milani is scheduled to map the composition of materials on and around Dimorphos, while Juventas will use radar to investigate the asteroid’s interior structure.
Juventas will attempt a landing on Dimorphos in what constitutes a major technological challenge, with Milani potentially attempting a landing as well. Hera itself carries a specialized camera, a laser altimeter, and a thermal infrared camera provided by the Japanese space agency. The combined fleet will operate together through early 2027, with the primary spacecraft continuing its survey operations through at least September 2027.