I think it would be cool if we could control a planet without owning it. This is what I think a subsidary planet does-
When you take a planet down to below 50 population, you may choose to make it your subsidary. It takes energy and credits but are scaled lower than normal colonies. You can have any number of subsidies at a time, but you can only keep a subsidary as long as 1 legion member is guarding the planet. (and be fore warned that you will automatically guard a new subsidary.)

You mean, like a tax that is payed to you, as if you had subjugated the owner, Middle Ages style?

Yes, it makes more flavor and strategy.

I see one problem with this.

If a player has 300+ legion, that means the player can theoretically have 300 extra planets being "taxed". Also, multi-accounts can abuse this, by having the primary account holder share alert, then level 1 multi's just occupy the planet.

1. do you honestly believe that 300+ people will protect the subsidies of 1 player? They are more likely to get their own. And I cannot think of anyone who has even 100 enemy planets scanned.
2. I see the problem with multi-accounts. Then how about the total attack of all suppressing legion members but be X3 the size of the planet? (representing the guard's intimidation required to suppress the planet) that would mean the guard of a large planet must have at least 153 attack.

I think this is a terrible idea i can see abuse in somany ways plus it gives incentive to make multi accounts.

Please elaborate on the abuse. I want to know how to fix it. Also, I just said:
If you think that is not enough, I'm fine with X4.

1. I used 300 legions as an extreme example. I was trying to put a point across that massive legions will reward those who randomly add strangers on FB for the games, while it would penalize those who don't like to add strangers on FB. Right now, the legion bonus is good enough with the % bonus to planetary stats, and the legion alerts.

More bonuses based on legion will only encourage more multi-accounts.

My solution is to either use your own attack power or rank to determine how many planets can be occupied. Perhaps one extra occupied planet per 200 attack, or every 20 ranks. This should keep the balance- imagine if a Rank 30 player with a legion of 100 manage to "occupy" 15 planets while ownig 9 (a total of 24 planets). That would throw off game balance.

2. I think a 6x would be better. I have Heavy Plasma weapons and if I mount 8 of them, I will have almost 500 attack. Heavy Plasma weapons aren't that high up in the research tier, and determined multi-accounts can easily reseach straight to that. If occupying a planet requires minimum of 500 attack, it shoud weed out 90% of multi-account abuse for this situation.

1. Good then. subsidary planets would be limited to rank. perhaps 1 every 20 ranks? It would be large enough to make it a fair adavantage to those who use it, while being small enough that it's not game breaking and would be less of a fear becuase at most it would effect 1/5 of all occupied planets (and only under perfect conditions). It would also be a reward to those coming out of beginner protection to be able to do it for the first time.

2. With requiring a 6:1 attack to size ratio, the required attack to suppress a planet would be (ordered smallest to largest):
126, 162, 198, 234, 270, 306, 342, 278, 414, 450
These are good numbers. Perhaps a little tweaking to extend the min/max, but this does make a balance as the bigger planets (more valuable ones) are harder to suppress.