Instead of having aliens and fancy interstellar weapons of all kinds from such a thing, how about adding a possible 'Impact Site', where a meteor came down and left a crater at a certain piece of terrain ? Though it's possible that there are more zombies at that place thanks to that, but it can also be worthwhile to check the buildings/places around the crater for extra loot and gear. Maybe you can also add radiation sickness when you go too close to the meteor itself. And when a meteor is too unrealistic for this, then maybe just use a crashed satellite instead - Since no one's keeping them maintained up there, many of them are prone to fall down to earth one way or another.
