Look in the .entity file under the GameInfo folder. Most mods have the entire resource
decrypted in their folder by now. But you can download it off this site. Look for the
forge tools option. For example, I'll use the PlanetIce.entity file:

crystalResourceAsteroidSetup
minCount 2
maxCount 4
extractionRate 0.400000
refineryRate 0.060000
maxRefineryCount 3

Artifacts are randomly placed on the planets in your map. You can increase the chance of
finding artifacts by going into Galaxy Forge, or by opening up your .galaxy map with
notepad, and set the probability of artifacts to 100%. That will place artifacts on every
planet in your map.