Options 1 and 3.
Planetarion is just entirely unsuitable for casual Facebook players, they'd probably get scared off and confused within 5 minutes. Reuse the Planetarion code and fork a new brand off just for Facebook users. Make it simple enough so that they could play alone instead of having to rely on others, but obviously it'll work better with friends.
Keep Planetarion as a separate brand, an advanced space game which requires more time and dedication. Maybe you could just implement
Facebook Connect instead to try improve signups. The game still needs massive improvements to gain and retain new users though, keeping it as a unique game doesn't excuse the fact that you need to improve the new player experience - Planetarion will slowly decline without fresh blood.
I think it's fairly obvious that you shouldn't put all your eggs in one gaming basket. Create more games under that Renegade Games brand. It's better to have a company with quality coders which spend part of their time improving all the games you own instead of a bunch of volunteers who can barely run a single game. Capture different segments of the market with different games. It's obvious that Planetarion isn't going to gain thousands of users anytime soon, but it could still have a long future as long as you keep on improving it.