Same thing happened to me. Couldn't find it on the map and the next time I was on the Citadel, it allowed me to talk to the Elcor Ambassador and complete the mission (without me doing anything). Might be a bug. If you can't find the planet, go see if it is already complete.
I just did a mission to find some kind of ancient thing there.. then I talked to the Ambassador.. and now I can't seem to do anything with the planet.. Did I do that other mission too early or start this one too late? --- GT: JamesBolton0723
I'm in the same situation as the above poster. Does anybody know the answer?
Edit: Scratch that. I just returned to the Citadel and talked to the Ambassador. I guess when I recovered the Artifact it counted the support mission as well. --- Currently playing - Mass Effect 3 Sent By Ravens - Mean What You Say - February 28th, 2012. Mass Effect 3 - March 6th, 2012.