So here's my idea for how the summoning item should work. (It's different from other summon items, because it's aliens from outer space, not monsters or humans from the same world.)
First the crafting recipe.
>5 Ectoplasm
>10 Hallowed Bars
>50 Martian Conduit Plating
1 Lihzhard power cell (to power up the beacon)
This summon item will also have to placed on the ground and be activated by a right click.
Once you right click the beacon, it will shoot up a beam of light and in a few seconds it will get destroyed in the process. Once it gets destroyed the event will begin.
Note: This item will have to be built at the Tinkerer's Workshop.