This nebula has been identified on side quests (I put all priority missions on standby ... ironically) so that I don't miss out on any content. Is this a case of a galaxy just not being available until the main plot line catches up?

How far do I have to progress to open these up?

4 Answers

The two IGN articles on them say that you gain access to them after the Priority: Thessia mission near the end of the game, so yes it looks like you need to progress through the main plot line to get them.

Priority Rannoch, I know this from personal experience

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The Cyone system within the Silean Nebula is available fairly early in the game. But there are systems within the Silean Nebula (Phontes and Teyolia -- maybe others) that do not become available until after Priority: Rannoch. I've just completed Priority: Rannoch and Hades Nexus is not yet showing on up the Galaxy Map.

Full Silean Nebula is available after Priority: Rannoch, while Hades Nexus seems to be after Priority: Thesia

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