When NASA's DART spacecraft hit the asteroid moon Dimorphos in September 2022, it proved that a collision can change an asteroid's path. But a test is only as useful as the measurements that follow it. Europe is now building on that result with two missions: Hera, already on its way to the impact site, and Ramses, a planned spacecraft meant to meet Apophis before its 2029 flyby.
DART was a one-way mission. Earth-based telescopes showed that the orbit of Dimorphos around its larger partner Didymos became about 32 minutes shorter, but they could only see two faint points of light. Nobody has yet measured the moon's mass, studied the crater up close or looked inside either body. Without those numbers, scientists cannot say exactly how much of the push came from the spacecraft itself and how much from rock thrown out of the surface. Our article on the DART mission covers the impact; Hera is the detailed "crime scene investigation".
Hera is a European Space Agency (ESA) mission that launched on 7 October 2024. Its target is the Didymos system: the main asteroid is roughly 780 meters across, while Dimorphos is a little over 150 meters wide (ESA quotes about 151 meters). Hera is expected to measure the mass of Dimorphos precisely, map the crater DART left and check how the surface and interior respond to an impact.
The route is not a straight line. In March 2025 Hera flew past Mars, using the planet's gravity to adjust its trajectory, and took the chance to image the small moon Deimos on the way. According to ESA, the spacecraft is on track to reach Didymos in late 2026, about a month earlier than first planned. Exact dates can shift, so check ESA's mission page for the latest.
Hera carries two shoebox-sized CubeSats, Milani and Juventas, that will be released near the asteroids after arrival. Milani studies the surface and any dust with a camera that sees beyond visible light. Juventas carries a low-frequency radar intended to probe the interior of Dimorphos, something no spacecraft has done for an asteroid before. If the moon turns out to be a loose pile of rubble, that matters a great deal: rubble absorbs and redistributes an impact differently from solid rock.
Hera also tests a practical idea: a spacecraft that can fly close to a small, weakly gravitating body and navigate on its own. Its cameras and a laser altimeter help it find its way around the two asteroids, because radio commands from Earth take many minutes to arrive. Those autonomy lessons will matter for any future mission that must act quickly near an unknown rock.
Ramses is ESA's planned mission to Apophis, the asteroid at the heart of this site. The idea is simple and ambitious: launch in 2028, reach Apophis before April 13, 2029, and stay with it while Earth's gravity passes by. Apophis will come within about 32,000 kilometers of Earth's surface (see our Apophis 2029 guide). That is closer than many satellites, and the tidal pull could squeeze and stretch an asteroid roughly 340 meters wide, possibly shifting loose material and changing how it spins.
Observing the "before and after" from nearby would show how a real asteroid behaves during a close encounter, which Earth-based telescopes cannot do in detail. ESA has described plans for CubeSats to accompany the main spacecraft, including one to study dust and probe the interior and another to study shape and geology, with an attempted landing. Reports also say the agency signed a contract with the Italian company OHB Italia for the spacecraft, and that Japan's space agency JAXA has joined as a partner. The mission is still in development, so details may change.
Apophis is not a threat, as we explain in Is Apophis Dangerous?. That is exactly why it is valuable: it is a safe, full-size practice target. Hera and Ramses together would give two different lessons. Hera tells us how an asteroid reacts to being hit. Ramses would show how a natural asteroid reacts to the gravity of a planet. Both feed the models used when planning how to deflect a real hazardous object, a topic we cover in Planetary Defense.
Facts in this article are drawn from public scientific sources. For primary information, see: