Anyhow, it's premature to even be worrying about ownership rights until some person actually lands there, and even then, there's ample historical precedent to guide us. If you're seriously interested in this topic, spend some time with exploration-age history, because space is likely to look a lot like that, only without the ethical issues associated with ignoring the natives, which at least our local space doesn't seem to have.
(And even if it does turn out Mars has some bacteria, well... Earth-bound conservationists are unlikely to hold back the progress for very long once it becomes a real possibility. It's really easy right now to posture about how we can't afford to colonize Mars if we would so much as tousle even one microorganism's precious little cilia, because the choice isn't real yet. When it is, someone's going to go.)