how to make a procedural destroyable planet?

I'm making a new game that involve generating planets where you can fly to each seperate planet and walk around it. Problem is I don't know how to make a procedural sphere that allows you to sculpt it by digging through to find cave and other secrets. I've looked around but couldn't find a thing. Also I'm new to scripting, I have only been learning for 2 month. Tutorials that will teach me to make my own script for it would be helpful.