Is there a chance for the proposed sites that was marked as closed to be open again? Is there a review for that to reopen sites?
You can appeal a closure, but in order to do so, you have to show how your site doesn't match the close reason. For your Mars proposal, you need to justify how it's not a duplicate of Space Exploration. What makes it different? How would those questions of yours be received there? Would they be allowed (barring other close reasons)? If they'd be on-topic there, but you want to try to make a go of the site, justify it's existence. What will this site do that it can't in Space Exploration?
In short, the onus is on you to show why it should be allowed.