How sure are we that people can stay healthy on Mars?
Not very. We know that no gravity is lethal in the long term for human beings (for a variety of reasons), but we really have no sense of where the cutoff is—moon gravity is probably too little, but we’ve no clue if Martian gravity might be enough. Human biology is definitely tuned to Earthly norms for obvious reasons, but it might benefit from greater or smaller g-effects; there simply isn’t enough research on the subject, as for obvious reasons it’s inordinately difficult to do the relevant studies.
Not very. We know that no gravity is lethal in the long term for human beings (for a variety of reasons), but we really have no sense of where the cutoff is—moon gravity is probably too little, but we’ve no clue if Martian gravity might be enough. Human biology is definitely tuned to Earthly norms for obvious reasons, but it might benefit from greater or smaller g-effects; there simply isn’t enough research on the subject, as for obvious reasons it’s inordinately difficult to do the relevant studies.