Hera
What is Hera?
Probes & telescopes· Launched 2024-10-07 – arrives 2026-12 (under way). ESA's probe returning to the asteroid that NASA's DART spacecraft deliberately struck in 2022. Arriving in December 2026, it will measure the results of the impact in detail to test this way of deflecting an asteroid.
Mission timeline
Spacecraft specs
| Launch | 2024-10-07 |
|---|---|
| Mars flyby | 2025-03-12 |
| Arrival | December 2026, Didymos system |
| CubeSats | Milani and Juventas |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
How Hera finds its own way around an asteroid
Hera will test how to operate near an asteroid without waiting for commands from Earth. Radio signals take tens of minutes to travel between Earth and the asteroid and back. When circling a 160 m moonlet only a few kilometres away, waiting that long for instructions would make it hard to avoid trouble in time.
So Hera's computer recognises the asteroid's outline and surface features in its camera images, works out where the spacecraft is, and chooses its own course. It is much the same idea as a self-driving car watching the road through its cameras. Once the method is proven, future probes could start their surveys much sooner after arriving at an asteroid.
Hera's two small companion satellites will talk to Earth through Hera. This link between spacecraft is the first test of such a network in deep space, beside an asteroid. The small satellites will fly closer to the asteroids than Hera itself, and at the end of its mission Juventas is planned to attempt a landing on Dimorphos.
The mission in depth
Protecting Earth from asteroids that might hit it is called planetary defence. One method is to crash a spacecraft into an asteroid to nudge its orbit. In September 2022 NASA's DART spacecraft tried this for real for the first time. Hera, the European Space Agency's first planetary-defence mission, is going to check the result on the spot.
DART hit Dimorphos, a 160 m moonlet circling the 780 m asteroid Didymos. It struck at about 22,000 km/h, and the time Dimorphos takes to go around Didymos became 33 minutes shorter. It was the first time people had deliberately changed the motion of a natural body in space.
Telescopes on Earth, though, could only measure the change in the orbit's timing. How big a crater formed, and whether the asteroid is solid rock or a loose pile of rubble, can only be learned up close. Hera was launched on 7 October 2024, passed Mars in March 2025, and arrives at Didymos in December 2026.
After arrival Hera releases two small satellites. Milani will study the surface composition, and Juventas will use radar to look inside Dimorphos. Measurements of mass and internal structure are what engineers need to work out how hard to hit a genuinely dangerous asteroid. Didymos itself poses no threat to Earth.
Frequently asked
- When did Hera launch?
- Hera was launched on 2024-10-07.
- What is the next milestone for Hera?
- Next for Hera, on 15 Nov 2026: Hera arrives at Dimorphos.
- In one line, what is Hera?
- Probes & telescopes — ESA's probe returning to the asteroid that NASA's DART spacecraft deliberately struck in 2022.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.