Create destructible objects

I started to use UA4 recently and I would like to create a simulation of space.

I work on an first person game, without gun or movement.
I already know the base. I created 2 “planets” as destructible objects. BUT the 2 planets destruct each other only if they are very close, when i get them far away from each other the collisions isn’t working, they just act like if there wasn’t collisions.

I hope it was understandable, I’m sorry for my bad English.
Thank you