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Is there an equation between the factor of Earth's gravity (the moon is (1/6)G) and how long a person can reasonably stay in that environment before returning to Earth would cause serious issues? Obviously humans would survive easier on a planet with say 7/8 of Earth's gravity or 10/9, etc, than something further on the number line like 1/8 or 5/3, which led me to my question.


Serious issues in the sense that they would need a cane to walk, or oxygen to breathe, a wheelchair, etc. Something that they used to be able to do on their own would need supplemental assistance because of the lack (or augmentation!) of gravity in the environment they spent time in. Is there a way to know the reasonable estimate before that happens?

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Fortunately for you we have human guinea pigs being subjected to the horrors of low G enviroments right now. They're called astronauts for some reason.

However, tests have only somewhat recently begun (only about 60 years ago) and because of certain ethical concerns (crazy, I know) we haven't actually locked any humans up there for more then a few years at a time so we really don't know the full extent of what low gravity does to a person.

Though broadly speaking we can say that extended periods in such conditions would lead to sharply declining bone density, damage (probably permanent) to the eyeballs and optic nerves (caused by the eyeballs being flattened), general muscles atrophy, the immune system becoming dangerously dysregulated, increased iron in the blood, issues in liver and kidney function and reduced digestion leading to malnutrition.

There are most certainly many other things that would start going wrong physiologically that we don't even know about yet.


So in short, this may be difficult to believe, but while we do know that low gravity will screw in innumerable ways with the human body we simply have no idea how long one can stay functional in it, mostly because we've never waited to see (because, apparently leaving the guinea pigs long enough up there until they start having disabilitating complications is "immoral").

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  • $\begingroup$ I think, there was some kind of investigation from earlier space days: astronauts / cosmonauts came back after weeks in space and had a lot of fatigue. Muscles built back, bones became more prone to break. Recall the old pictures shortly after reentry, when they were just incapable to walk on their own. That was basically the moment, it was decided folks actually need to exercise in space. $\endgroup$ – Oleg Lobachev Nov 5 '17 at 23:16

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