Hera closes in on the asteroid DART impacted

The European Space Agency's Hera spacecraft has captured its first close-up image of the Didymos asteroid system, revealing previously unseen terrain on the 780-metre-wide parent asteroid Didymos. The monochromatic Asteroid Framing Camera acquired the image from 60 kilometres away, showing boulders, craters, and possible grooves or ridges across Didymos's surface. The smaller moon Dimorphos, which measures 151 metres wide, appears mostly in shadow in this view.

Hera is conducting a detailed examination of what NASA's Double Asteroid Redirection Test (DART) accomplished when it struck Dimorphos in 2022. That impact shortened Dimorphos's orbit around Didymos by approximately 33 minutes, exceeding predictions and marking the first time humanity measurably altered another Solar System body's orbit.

Key questions remain unanswered. Scientists do not yet know whether DART simply excavated a crater or fundamentally reshaped Dimorphos. The asteroid is believed to be a weakly bound rubble pile, meaning the impact could have rearranged its internal rocks rather than creating a simple impact hole. Material ejected during the collision may have provided additional recoil force, and some researchers suggest Dimorphos could now be tumbling rather than rotating in synchronisation with Didymos.

Michael Küppers, ESA's Hera Project Scientist, said determining Dimorphos's mass is essential. "With this we will know how efficient the impact was," Küppers stated. "The secondary effect may even have been stronger than the direct impact effect. But to really know this, we need to know the mass."

ESA will release detailed images of both asteroids on 25 November. After its initial survey, Hera will deploy two CubeSats named Milani and Juventas. Milani will study Dimorphos's surface, composition and dust environment, while Juventas will use radar to investigate subsurface structure and search for large internal blocks, voids, or debris. Together, these measurements will reveal how loosely packed the asteroid is and how it responded to DART's impact. Those findings will inform humanity's approach to planetary defence if an asteroid ever poses a threat to Earth.