Or do as one of my characters in a M&M game did, and send the entire problem to a universe where Earth was overrun with zombies.
As a note, it is fun to watch a DM's reaction when, faced with an imminent alien invasion, you skip off to your home outside of time and space to look for a convenient parallel dimension that has zombies running around all over the place, and design a ritual that will open a portal large enough to send the entire alien invasion force to that world.
We had to promise him that 'send them to the zombie dimension' wouldn't be our standard ploy for dealing with threats.