[Pitch]

Now it's time to populate the area with smaller rocks to give the illusion of it breaking up.

Select the asteroid using the same method described earlier and copy it (Ctrl + C). Now paste it using Ctrl + V. This will be put automatically into a new layer.

Use the transform tool (Crtl + T) and shrink, stretch and spin the new asteroid. Basically go nuts. Once happy with the new rock, hit Enter and begin over with another one

Do this until you have the desired concentraion of asteroids.

Here's what mine looks like.