Planets being knocked out the way

I have these planets. They’re kinda on a little prince scale. Fairly large but cute.

The UE4 auto weight calculation for this one I’m looking at is 13million kg. I’m okay with that.

Problem is that some objects knock these planets out of orbit (eventually my physics will bring them back, but it can take a while). This happens when a tractor beam pulls an object into a planet, or when an object spawns inside the planet.

How do I make sure my planets never really get knocked around by other objects?