Asteroid moonlet Dimorphos as seen by the DART spacecraft 11 seconds before impact. (NASA/Johns Hopkins APL)

On September 26, a NASA spacecraft crashed into an asteroid. This collision was no accident. It was an experiment. Scientists were trying to change the asteroid’s orbit.

Why? To test a way to protect Earth against potentially dangerous asteroids and comets.

An ounce of prevention

Our solar system is full of asteroids, the rocky remnants of its creation 4.6 billion years ago. Earth gets hit with them every day. Most are tiny and harmless, but every once in a while, an asteroid comes along that is big enough to do a lot of damage.