Would a group of free, equal and rational people necessarily agree on a set of rules for live by? If not, is this a problem for contractarianism?

Yes, it's a problem

Explanation:

Simply because all can't agreed on a set of rules, kinda hard though but anyway in the group, they're still passionate fellows.

giant impact theory - the moon was formed from the collision between earth and another mars-sized body.

colliding planetesimals hypothesis - the moon was formed from the same cloud of material as earth.

capture hypothesis - the moon was locked into orbit by earths gravity as it was passing by it.

accretion hypothesis - the moon was formed from collisions and combining of planetesimals.

i think this is right, if not and you know better let me know.

answer; can each be concretely realized in different ways;