Epiphrons

SO I've been playing the demo for the last few hours while the steam beta downloads, this game will obviously be amazing. Quick question, When shooting down ufo's, is their a chance for them to be destroyed? or is this based on the amount of damage you do? the last 5 or so run in's I have had with the enemy have all ended in ufo destruction and I am itching for some ground combat. Apologies if this is answered somewhere.