WhatIsSol: You cannot rename individual planets but can rename star systems.
Just go to any planet screen in the system that you own - right after planets name will be a small blue pen icon. Just click it and a popup will appear allowing you to change the system name.
Hi! Thank you for the help!
I was certain that I was able to name individual planets in some form in my games as I had the 12 colonies of Kobol in my previous install of MOO. I was hoping to be able to recreate that, but I guess either something was changed or my memory is not that good. Still, being able to name systems is already a plus.