I found the sugarcraft's page on what the differences between pearl, petal, and luster dusts are...http://www.sugarcraft.com/catalog/coloring/dustinfo.htm

But it's more for the effects given to flowers.

How about if I want to brush dust directly on a cake covered with blue fondant? The theme is stars, night, universe, and I want the blue fondant background to sparkle.

Which dusts is best for this? I plan on using Satin Ice blue fondant because I don't trust my MMF to withstand to a deep dark cosmic, outer space blue

Everything you want to know about the different dusts:
(Has application methods, hints & tips.)

http://cakecentral.com/cake-decorating-ftopict-54059.html

HTH