Nancy, you might want to check out the carnivals we've done already here at AW to get a better idea. The carnivals I've written for and the one I hosted germinated here.
When Ben did the first FFC he established that it should be open to everyone in any genre and that only the theme, as established by him, would be the common element. Well, there's the flash word limit aspect too, of course.
BunnyGirl types a bit about each story she hosts in her holiday-themed carnivals. I didn't do that. I just posted links. Now it's true that for the stories I hosted in my own blog for other writers I tried to include a bit of biographical information about the author at the beginning of each piece so as to differentiate each one from me a bit more, but I didn't do even one sentence synopses of the stories because with twenty writers that would've taken forever!
And sure, there's no reason you can't host one yourself. If you are too specific with your theme you might not get very many participants, but that's your decision. It's YOUR carnival, after all. To follow the theme of your interstellar example, you might want to theme a carnival by region. The various regions in the US and Canada, then Mexico, then Central and South America. You might go by country in Europe and Asia too, depending. I know that people do bike tours all over the world, so I can see this working very well for you. You may wish to make the point that you're seeking non-fiction accounts, unless of course you're open to fictional ones. That might be interesting, actually.
It's a lot of work. You have to confirm that the participants did author their pieces and then get the coding done for the links, but that turned out to be time consuming more than difficult.
Is this helpful to you at all?