Just on MB's recent comment :
MB said:
"And to those asking why nebulae - it's quite logical if you think about it

"
I'm no astronomer so am theorizing here about something I know very little about..
Is MB's stated association of nebula and barnacles actually direct, or is it indirect?
The Pleiades nebula has a bunch of blue (b class) stars.
As in, is the occurrence of these types of stars correlated with nebula, meaning the barnacles could be more to do with the properties of the star (and hence the planets) than the nebula as such, the nebula just being a likely side-effect of the type of star?
Been googling to see if b class stars and nebula are correlated, found this not sure if it's actually true though. =p
http://www.howitworksdaily.com/why-are-some-stars-blue/ said:
"In fact, these are rare ultra-blue stars – old red giants past their prime that have ejected most of their surface material to expose hot blue cores. This much ejection is unusual and likely happens because they are richer in chemical elements other than the normal helium and hydrogen, which makes it much easier for the star to slough more layers into space."
So perhaps.... Some older blue star have ejected rich elements, often this will result in a nebula.
These rich elements are used by barnacles in the production of meta-alloy.
Blue stars + nebula being an indicator of an environment suitable for placing a meta-alloy production facility?