ESA Hera Arrival at Didymos Binary Asteroid

What this countdown tracks

ESA's Hera spacecraft arrival at the binary asteroid system 65803 Didymos and its moonlet Dimorphos, beginning in late November 2026 with the early-characterisation phase and continuing into formal orbital insertion in early 2027. Hera is the European follow-up to NASA's DART mission — the Double Asteroid Redirection Test that deliberately impacted Dimorphos on 26 September 2022 — and will conduct the most detailed survey ever made of an asteroid following a kinetic-impact deflection.

About this mission

Hera was conceived as the European partner mission in the AIDA (Asteroid Impact and Deflection Assessment) collaboration, led by ESA's Space Safety programme and built by an OHB-led industrial consortium with Avio, Thales Alenia Space, GMV, Spaceopal and dozens of European subcontractors. The spacecraft launched on 7 October 2024 from Cape Canaveral on a Falcon 9 rocket and used a March 2025 Mars flyby with a deflection encounter of Mars's tiny moon Deimos for trajectory shaping and bonus science. Hera carries two CubeSats — the Italian-led Milani and the Luxembourg-led Juventas — that will be deployed at Didymos to perform close-range mineralogy and the first asteroid-surface radar tomography respectively.

The science target is the binary asteroid 65803 Didymos and its small moonlet Dimorphos. Didymos is roughly 780 metres across; Dimorphos was approximately 160 metres before the DART impact. DART's 14,000 mph kinetic strike on 26 September 2022 reduced Dimorphos's orbital period around Didymos by approximately 33 minutes, far in excess of pre-impact predictions, and ejected an enormous comet-like dust trail observable for months from Earth. Hera's mission is to follow up on the impact crater, the resulting shape change, the regolith and porosity properties, the binary's mass and density, and the precise orbital evolution post-impact — converting DART's qualitative deflection result into a quantitative model that planetary-defence programmes can scale to other asteroid scenarios.

Mission objectives

Watch for the late-2026 early-characterisation phase as Hera approaches Didymos at low relative velocity, the initial high-resolution imaging of the DART crater on Dimorphos, the deployment of the Milani and Juventas CubeSats in the binary's chaotic orbital environment, the first ever asteroid-surface radar sounding of Dimorphos's interior structure (Juventas), thermal infrared and visible-and-near-infrared mineralogy from Hera and Milani, and a planned slow descent to the binary's L1 region. ESA has stated that the prime mission concludes after roughly six months at the binary; an extended-mission landing on Dimorphos's surface at the end of operations is under consideration. The data set will inform planetary-defence playbooks and also tell us a great deal about the formation and structure of small near-Earth asteroids.

Past missions

• DART — 24 November 2021 launch; 26 September 2022 impact at Dimorphos. First-ever planetary-defence kinetic-impact demonstration.
• Hayabusa2 (JAXA) — sample return from asteroid Ryugu, capsule recovered 6 December 2020.
• OSIRIS-REx (NASA) — sample return from asteroid Bennu, capsule recovered 24 September 2023; the spacecraft continued to Apophis as OSIRIS-APEX.
• Rosetta (ESA) — landed Philae on comet 67P/Churyumov-Gerasimenko on 12 November 2014.
• NEAR Shoemaker (NASA) — first asteroid orbit and landing, on 433 Eros in 2000–2001.

How to follow

ESA's Operations Centre in Darmstadt, Germany (esoc.esa.int), and the Hera mission page at esa.int publish flight events, images and trajectory updates. The European Space Operations Centre operates Hera through the ESTRACK 35-metre antennas at New Norcia (Australia), Cebreros (Spain) and Malargüe (Argentina). Independent space-media coverage runs through Spaceflight Now, the Planetary Society, BBC Science, Andrew Parsonson at European Spaceflight, the SpaceQ podcast, and ESA's own ESA Web TV. The DART mission anniversary (26 September 2026) typically gets parallel coverage from the Johns Hopkins Applied Physics Laboratory.

Related countdowns

The Hera arrival sits alongside Chandrayaan-4 launch, Artemis III launch, and Chang'e 7 launch on the active 2026–2027 deep-space mission calendar. Other planetary-defence and small-body missions to track include the NASA Dragonfly launch (Saturn's moon Titan) and the NASA Roman Space Telescope launch.

FAQ

When does Hera arrive at Didymos? Late November 2026 for the early-characterisation phase, with formal orbital insertion in early 2027. Where is the target? The binary asteroid 65803 Didymos and its moonlet Dimorphos, currently around 0.21 AU from Earth at arrival. Why does the Hera arrival matter? It is ESA's lead planetary-defence mission and the first detailed scientific survey of an asteroid that has been deliberately deflected by a kinetic impact (NASA's DART, 2022). Who runs the mission? ESA's Space Safety programme leads, with an OHB-headed European industrial consortium and Italian and Luxembourg-led CubeSats Milani and Juventas.