An unusually high number of planets were at the minimum quality (Normal difficulty * minimum quality of 10 for Carbonaceous gives 8.5 and gets rounded to 9.
A sample size of 150 I chose because you tend to be able to observe a normal distribution pretty well around that size.
I boosted the number of Carbonaceous planets that were in existence by massively increasing the OrbType chance to 0.4.

Erik, can you confirm whether this is expected behaviour? Unless there's some hidden correction behind the scenes where it skewed the quality due to sheer number of Carbonaceous planets, idk what to think.
What's more bizarre is those massively out of range planets - I observed three planets that were far in excess of the normal quality range of Carbonaceous worlds.