Hera

Key facts

Mission & specifications

Mission

Hera is Europe's half of the first real test of planetary defence — the idea that humanity could, if it ever had to, nudge a dangerous asteroid off a collision course with Earth. It is the second act of a two-mission experiment. In 2022 NASA's DART spacecraft deliberately slammed into Dimorphos, the small moon of the asteroid Didymos, and measurably changed its orbit — the first time people had altered the motion of a celestial body. But DART was destroyed on impact, leaving key questions open: exactly how much momentum was transferred, what the crater looks like, and what Dimorphos is really made of. Hera, launched in October 2024, is flying out to answer them. When it reaches the Didymos system in late 2026 it will spend months studying both asteroids in detail — weighing Dimorphos, examining DART's crater, and probing the internal structure. Knowing the mass and the crater precisely turns DART's one-off success into a calibrated, repeatable technique that engineers could trust in a genuine emergency. Hera also carries two shoebox-sized CubeSats it will release for even closer approaches, including the first radar sounding of an asteroid's interior. Together, DART and Hera are meant to move planetary defence from a thought experiment to a tested capability — the first careful steps toward a world that can, in principle, protect itself from the kind of impact that ended the age of the dinosaurs.

1. 2024Launch toward DidymosLaunch

   ESA's planetary-defence mission sets out to follow up the DART impact.

2. 2025Mars gravity assistFlyby

   A swing past Mars bends Hera's path toward the asteroids, with a bonus look at Deimos.

3. 2026Arrival at Didymos (planned)Arrival

   Hera is due to reach the Didymos–Dimorphos system to survey DART's crater up close.

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