NASA’s Double Asteroid Redirection Test (DART) spacecraft, which collided with the moonlet Dimorphos in September 2022, changed the orbital period of the Didymos-Dimorphos binary system around the Sun by 0.15 seconds. The 770-day solar orbit shifted due to the impact’s momentum and ejected debris, marking the first measurable alteration of a celestial body’s path around the Sun by a human-made object.
Didymos, approximately 805 meters wide, hosts Dimorphos, a 170-meter moonlet that orbits it every 11 hours and 55 minutes pre-impact. DART struck Dimorphos at 22,500 km/h, shortening its orbital period around Didymos by 33 minutes—exceeding the 73-second success threshold. The collision deformed Dimorphos, creating a crater and altering its shape from a likely prolate form, potentially inducing chaotic tumbling as it seeks gravitational equilibrium with Didymos.
Debris ejection provided a momentum enhancement factor of about two, doubling the spacecraft’s deflection effect as material escaped the system. This recoil slowed the binary pair’s solar orbit by over 10 micrometers per second. Researchers confirmed the changes using ground-based radar, stellar occultations—where the asteroids briefly eclipsed stars—and observations from October 2022 to March 2025.
The non-threatening binary system served as a testbed for kinetic impactors in planetary defense. Didymos’ rigid structure remained unchanged despite mass loss to form Dimorphos. European Space Agency’s Hera mission will provide further data later in 2026.