Huge impacts and explosions take place in space all the time. Why do we not hear them?

The reason is that the production and movement of light requires a substance that can vibrate. 

In space, these substances are few and far between. As a result, no vibrations or sound waves can be formed. 

On Earth, the situation is different. Here, the air can act as a medium through which the vibration can reach the listener's ears. 

Sound travels well through the atmosphere. However, it moves even better through water and iron. In empty space, it cannot move at all.