nope

I'm unsure you are accpeting the right answer here.  When you find an artifact you get that ability for as long as you hold the planet in which you found the artifact.  If, on another planet you find another artifact, no you get that benefit for as long as you hold said planet.  If both planets are in your possession, then you get both artifacts.  Therefore, either Ryat is fooling around with you, or he just doesn't know what he is talking about.

^Yeah, the only advatage of having two of the same artifact is that you are less likely to lose that artifacts advatage. It's like building more than 8 research labs, the extra don't do anything unless the others are destroyed.

Ahh yes,  whoops.  Well i forgot the multiplicity of artifacts.  And yes, you got your answer