[Rexxx]

Just for the records:
I did some tests and the result is "random". The 12-9-0 series probably was just bad luck.

The numbers:
The results for a level 3 planet creator:
Out of 97 asteroid fields (medium up to huge) 48 rock planets, 33 gas giants and 16 ice planets were created.

For a level 1 creator:
51 asteroid fields (medium up to huge): 30 rock planets, 11 ice planets and 10 gas giants.