In 2022, NASA's Double Asteroid Redirection Test (DART) spacecraft slammed into the pyramid-sized asteroid Dimorphos, which orbits the much larger 65803 Didymos. The collision was part of a project to test ways to protect the Earth against the threat of dangerous asteroid impacts.

One would think that the experiment ended two years ago, but when the impact occurred the asteroid pair were 6.8 million miles (11 million km) from Earth, which made observing the event a bit like target shooting at a rifle range without any binoculars to see where the bullet landed.

A grainy video of the event was captured, and ground-based telescopes have been estimating how the impact changed the orbit of Dimorphos and the collision debris. The best estimate is that the impact altered the period of the orbit of Dimorphos around Didymos by 33 minutes, or by almost 5%, and a debris plume spewed into space. However, the only way to really assess the effects is to go to the asteroid directly.

About the size of a car, Hera is tasked with making a detailed assessment of the impact as well as a complete survey of the asteroids, since the composition and structure can have a serious effect on an attempted deflection. If the asteroid is hard and metallic, it will be elastic and respond accordingly. If it's just a collection of loose rubble, it will respond in a completely different way.

When it arrives at Dimorphos in about two years, Hera will seek to learn the exact size of the impact crater, how the impact deformed the asteroid, as well as the mineralogy, structure and precise mass of Dimorphos. To do this, it will bring to bear a hyperspectral imager, a laser altimeter, a thermal infrared imager, and a radio instrument that measures the Doppler effect to determine the mass of both asteroids and the nature of their gravitational fields.