You can terraform a planet but you cannot change its size. 

That does make sense but maybe we could introduce something that would change it.


We have a planet destroyer weapon so maybe after destroying a planet you would be able to harvest what is left and use it to increase the size of an existing planet or maybe even create a new one in a different system.


A new planet would start as Barren (nothing else seams to be appropriate) and you would be able to terraform it to better ones.


After a planet destruction you would be left with a number of resources:

0 - Tiny

1 - Small

2 - Medium

3 - Large

4 - Huge


1 resource can be used to:

- increase planet size

- create a tiny planet


You wouldn't be able to create a huge planet right away but would need to start with small and move up.

Also as you see after a planet destruction you get less resources than are needed to build it.