ESA’s Hera mission, launched in October 2024, is now en route to the Didymos binary asteroid system to complete the first full-scale test of planetary defense begun by NASA’s DART impact in 2022. By arriving in 2026, Hera will transform a headline-grabbing collision into quantified science, measuring how the kinetic strike altered Dimorphos and its orbit. The mission aims to turn a successful demonstration into an engineering blueprint for future asteroid deflection strategies. It is a tightly coordinated international effort designed to answer how, and how well, humanity can nudge a hazardous object off course.
Hera is a follow-up investigation to NASA’s Double Asteroid Redirection Test, which intentionally struck the moonlet Dimorphos and shortened its orbital period around Didymos. DART proved deflection by impact can work, but many crucial parameters—such as the efficiency of momentum transfer and the detailed surface response—remain uncertain. Hera’s close-up survey will provide the missing physical context by mapping Dimorphos, characterizing the impact site, and precisely tracking the system’s dynamics. Together, DART and Hera form a two-mission experiment that bridges demonstration and diagnosis.
A central goal is to quantify how asteroid material properties shaped the outcome. Hera will determine the mass and density of Dimorphos, refine its shape model, and measure the crater formed by DART. Radio tracking and navigation data will be used to derive the gravity field, constraining internal structure and porosity. These measurements will feed directly into improved impact simulations and risk assessments for future deflection attempts.
The spacecraft carries optical cameras, a laser altimeter, and thermal sensing to build high-resolution maps of both Dimorphos and Didymos. Two small companion CubeSats—Milani and Juventas—will be deployed during operations for close-range investigations. Juventas will probe the interior using low-frequency radar to reveal the moonlet’s internal architecture. Milani will perform hyperspectral and dust studies, helping link surface composition, regolith behavior, and the plume dynamics triggered by the impact.
Hera is scheduled to arrive at the system in 2026 for a months-long survey, gradually tightening its approach as navigation confidence grows. Early approach imaging will refine asteroid properties and ensure safe deployment of the CubeSats. By the end of the campaign, scientists expect a definitive assessment of the DART crater, the momentum enhancement factor, and the binary’s post-impact state. The results will anchor planetary defense planning with real-world data, advancing international readiness for any future asteroid threat.
