Two years ago, a NASA spacecraft gave a small asteroid a big whack. And two years from now, a European craft will study the aftermath of that impact. It should reveal how the asteroid has changed, and why the impact was so effective.

The impact took place in September of 2022. A projectile as big as a van slammed into Dimorphos, the smaller member of a binary asteroid. It’s about 500 feet across, compared to half a mile for the larger member, Didymos.

The original mission was a test of a way to deflect an asteroid on a collision course with Earth. And the test worked – it changed the smaller asteroid’s orbit by much more than expected.

But to fully evaluate the results, scientists need to know more about the asteroid, and about what happened to it after the test. And that’s the job for Hera, the European mission. It’ll study the asteroid’s composition, and see how the impact changed its shape. Early studies of the impact say Dimorphos is a “rubble pile” – chunks of rock barely held together by gravity. It could have formed when material spun off the surface of Didymos, then stuck together.

Hera is scheduled for launch this month. It’ll fly close to Mars in March, using the planet’s gravity to get a “kick” toward its target. Hera should enter orbit around the asteroids in two years. And it will deploy two small sub-satellites – one to study each member of the binary asteroid.

Script by Damond Benningfield