"those who can exercise violence" is pretty good approximation of whose in charge. After all, every government on earth, of whatever type, have a legal monopoly on use of violence. In modern democracies this is in theory used only to uphold the law and in any case as a last resort.
Whether Mars et. Is ruled by earth government proxies, corporations or is independent, whoever is in charge needs to have (or be backed up by) the biggest guns.
Incidentally with months-long round trips, whoever is in charge will be pretty independent anyway