Europe's Hera Spacecraft Begins Close Investigation of NASA-Impacted Asteroid

The collision was anything but tidy. Dart sent rubble and even boulders flying off the moonlet's surface, and that escaping debris provided an extra kick of momentum beyond the spacecraft's own impact — a recoil effect, working much like the thrust from a rocket exhaust. The debris trail stretched more than 10,000 kilometers into space and persisted for months.

Scientists say some of that debris could still linger in the vicinity, which adds a note of caution to Hera's increasingly close approach.

What happens next month?

Hera is not finished closing in. Next month, the spacecraft will venture to just 12 miles (20 kilometers) from the asteroid pair, an approach that ESA officials describe as worthy of the agency's finest robotic detective.

To conduct the survey, Hera carries 25 science instruments. It also transports a pair of shoebox-sized satellites known as Cubesats (miniature spacecraft built from standardized modular units), which will survey Dimorphos even more closely than the mother craft can and attempt to land on its surface.

A successful landing would give researchers their first direct contact with a human-made crater on another world's small body — the definitive physical evidence of how the asteroid responded to a high-speed impact.

Why does a four-year-old crash site still matter?

The Dart test proved the principle: hit an asteroid, and it moves. But principle is not precision. Hera's measurements will tell scientists how large a crater the impact excavated, how the asteroid's interior is structured, and how much of the orbital change came from the momentum of the collision itself versus the recoil from ejected debris.

Those numbers matter because any future real-world deflection would have to be calculated before the fact. A mission launched to divert a genuinely hazardous asteroid would need to know, in advance, how much a given impact would shift its target. Hera's findings will convert a successful demonstration into usable engineering.

The preliminary nature of the work cuts both ways. Hera has only now begun its close observations, and the detailed results — including the Cubesats' attempted landings — lie weeks and months ahead. What the spacecraft has established so far is position and readiness: it has arrived, it holds its station at 25 to 30 kilometers, and its instruments are trained on the crater NASA left behind in 2022.

Four years after the impact, the detective has reached the scene.