You are creating very extreme displacements which can create holes like this. The normal fix is to increase Displacement Tolerance in the Planet object. A value of 2 usually fixes such problems, but yours is very strong. Even a value of 5 does not fix it totally. I would suggest rethinking or adjusting how you are creating this effect because it is not creating very good geometry (from heavy and/or overlapping displacement) for the renderer to work with.
- Oshyan