You would want to use a particle emitter/system. Probably 1 layer would be the snowball, and as it hits the lens, it explodes into particles. Trapcode Particular or the CC Particle systems probably could create the explosion. You might also experiment with the Simulation > Shatter effect to create this type of effect.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.