A hitchhiker’s guide to Hera’s target asteroids

What happened

Currently speeding through deep space at 12 km/s relative to Earth, ESA’s Hera spacecraft is due to reach its target Dimorphos asteroid this November. Size guide to Hera and its target asteroids To start with, Hera is actually headed for two asteroids rather than one.

Dimorphos – at 151 m across about the size of the Great Pyramid of Giza – is actually orbiting around the mountain-sized 780-m diameter Didymos asteroid. Both asteroids are made from relatively dark silicon-rich rock.

Didymos and Dimorphos seen by DART The two asteroids are extremely different, as observed by NASA’s DART spacecraft just before it impacted the smaller of the two on 26 September 2022 . The challenge is that the gravitational pull of the larger Didymos body is much stronger than Dimorphos’s: the former has gravity about 40 000 times weaker than Earth's, while Dimorphos has about 200 000 times weaker gravity than Earth’s.