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I've been thinking about proposals to live on Mars. One idea is to create an artificial magnetic field to protect from solar radiation. Another idea is to warm the planet using solar mirrors. In the meantime, while terraforming the planet, we could live in a dome or some kind of controlled habitat, which protects from solar radiation and gives a breathable environment. However, there's one problem, and that is gravity.

Gravitational acceleration on Mars is 38% of what it is on Earth. Does lower gravity on Mars make it unsafe and unhealthy for humans?

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    $\begingroup$ @uhoh I deleted the strikethrough text but am preserving it here: "I guess this question partly depends on whether it is possible to create artificial gravity, e.g. using a rotating habitat." $\endgroup$ – ktm5124 Mar 23 at 22:11
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    $\begingroup$ FWIW, many SciFi authors have taken it as a given that "native" Martian humans would be serious health risks if they went down Earth's gravity well. That always seemed reasonable to me. $\endgroup$ – Carl Witthoft Mar 24 at 14:07
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    $\begingroup$ Comments are unfit for preservation (they can be removed at-will). If you have a second question, post a second question. $\endgroup$ – Mast Mar 24 at 14:46
  • $\begingroup$ Note that there's no need for generating magnetic fields to keep the solar winds out, provided you choose your location accordingly, e.g. in Terra Sirenum. The crustal magnetic fields of Mars are so strong there that they create so called "mini-magnetospheres" which ward off the solar wind. Whether your electronics will function properly over there is another question though. $\endgroup$ – Adriaan Mar 25 at 15:44
  • $\begingroup$ The growth and health of children conceived and born and raised under such conditions looks more significant for any potential colonisation than how the health of Earth raised adults is effected. Perhaps live animals will be sacrificed to find out before humans try it. SciFi is not a good source of information; some writers chose to portray lower gravity of Mars and Earth's Moon as good for human health and longevity with zero evidence in order to help encourage and promote space exploration. Better to actually know before sending colonists. $\endgroup$ – Ken Fabian Apr 2 at 0:41
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This is actually a good question, and one that we really don't have a good answer to. Intuitively it must be better than zero gravity, but the question is, will it be good enough. There are a host of problems associated with long term living in zero gravity, including loss of bone strength and others, it is not currently known if Mars is good enough.

The only way to really answer this question is to either send humans to Mars, or set up some kind of an orbital centrifuge to try and determine this.

Lastly, artificial gravity on a planet wide scale is not really possible, although theoretically one could spin a city to provide artificial gravity, similar to a spinning orbital habitat. That seems unlikely to help much, but it might be good enough for some kind of exercise.

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    $\begingroup$ We don't know what level of gravity is required, so that would be basically impossible to answer. But spinning laboratories have been done on Earth before, so it should be possible on Mars. $\endgroup$ – PearsonArtPhoto Mar 23 at 22:40
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    $\begingroup$ It's amazing how much effort and money we've put into space exploration and we still don't know the answer to this question. It shows how far we have to go and how long it will take us to get there. Space really is long term. $\endgroup$ – GdD Mar 23 at 23:54
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    $\begingroup$ @ktm5124 there are currently about 70 questions here tagged with artificial gravity. I think a new question asking about the use of centrifuges to augment gravity already present on a planet would be wonderful, and lead to some interesting answer. $\endgroup$ – uhoh Mar 24 at 1:15
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    $\begingroup$ "Artificial" or "Augmented" gravity are very expensive options. SInce Mars has a decent gravitational force, why not provide residents, or at least those planning for a return to Earth, with weighted jackets, pants, shoes, etc. so the effective force they have to exert to walk, lift their arms, etc. is equivalent to an unweighted body in one-g ? $\endgroup$ – Carl Witthoft Mar 24 at 14:09
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    $\begingroup$ @CarlWitthoft Although you can add some strain that way the exact weight/strain distribution on the body is quite different from the effect of gravity. By external loading you place mainly stress on muscles/tendons and bones, but it does almost noting to simulate the effect of gravity on the cardovascular system and the internal functioning of the organs. It just doesn't model the effects of gravity properly. $\endgroup$ – Tonny Mar 24 at 14:30
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Let's quickly take a glance at the boundaries of the parameter space.

  1. As we know, the lower extreme, zero gravity, is pretty unhealthy for humans in the long term. Some effects have been known for some time, like bone and muscle deterioration, and effects linked to changed body fluid dynamics. Other effects were detected more recently, like the epigenetic changes in Scott Kelly. In fairness, epigenetics is in itself a relatively recent field of research, but this realization simply adds to our uncertainty: There are probably some "unknown unknowns" regarding humans in zero gravity, simply because there are many unknowns about humans in general. Dare I say it here? Humans are more complicated than rockets ;-).

    There are also indications that zero gravity affects reproduction in more ways than immediately come to mind.

    On the other hand it has been shown that a year in space is not life threatening or debilitating. We can safely assume that humans can survive in zero gravity for a number of years, albeit with accumulating complex health problems.

  2. Looking at the other extreme, it is also very likely that 1g is the gravity our body performs best in: It is specifically designed for it. Vessel layout and size, bone properties, tissue properties, heart parameters, migration of solubles in the body: It is all designed to work well and in many cases exploit exactly 1g while running around in a savanna.

These extremes span the expectation space for the effects of Mars gravity, 38% of the likely ideal. We can assume that the health effects of low gravity do not scale linearly, so that living under 0.38g does not mean to have 62% of the health problems one would have under 0g; it is probably much less. If life expectancy in zero gravitation is already a number of years, is will be substantially more in 0.38g, albeit probably with slowly accumulating health problems. The big question is whether one would live long enough to prosper, in particular to reproduce and pass one's knowledge on to the next generation, a question which can only be answered experimentally. As a wild guess I would say that most effects observed in zero gravity will be modest in 0.38g, with an exercise regime added. Of course there may be synergies with other negative health effects from bad nutrition, radiation, lack of running around in a savanna etc. Overall survival will depend on solving a lot of problems — all of them — sufficiently well.

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  • $\begingroup$ It is not only the stay on Mars, it is also the long flight to Mars and back to Earth later. Both in zero gravity. There will be no support crew on Mars like on Earth when returning from a long stay at the ISS. $\endgroup$ – Uwe Mar 24 at 18:38
  • $\begingroup$ Depends on how advanced the space taxis are. If you had large cyclers, it is possible they would have artificial ring gravity. But yeah, the first generation ships, a la Musk's Starship will almost certainly be 0g. $\endgroup$ – Lawnmower Man Mar 24 at 22:43
  • $\begingroup$ I thought that most of Scott Kelly's health issues were attributed to increased radiation exposure while in space, not the lack of gravity. Not that weightlessness isn't an issue, but it's the more minor of the two factors. $\endgroup$ – Darrel Hoffman Mar 25 at 16:40
  • $\begingroup$ @DarrelHoffman Good point. It's a mix of effects and a mix of reasons, according to a nature article. Chromosome changes and flips may be due to radiation, other changes seem stress related. Zero gravity is probably one stress factor. $\endgroup$ – Peter - Reinstate Monica Mar 25 at 20:36
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    $\begingroup$ Technically the "other extreme" would be a black hole, but that's not a particularly useful thought experiment to carry out for the question asked... $\endgroup$ – T.E.D. Mar 26 at 13:43
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Well, Scott Kelly and Valery Polyakov survived in microgravity for more than a year (continuously) and re-accustomed back to 1 g on Earth. On Mars, the crew would spend about a year and this time in gravity so even though the gravity is much lower it would be better to adapt to it and re-adapt to the Earth's gravity than in the case of microgravity. You might argue that the spaceflight to and from Mars takes place in microgravity but NASA's concepted Mars spaceship, the Nautilus-X spacecraft, shall create a rotational artificial gravity of up to 0.69 g so the astronauts would be in an even higher gravity than on Mars. It was hard for Scott Kelly but he eventually re-adapted to the Earth's surface gravity. It wasn't that hard for Valery Polyakov (who was a doctor/physician or something) because he as a physician had prepared very well for his spaceflight and followed a rigorous exercise regime. So although he was a bit longer in space than Scott he somehow managed it very well. For the Martian explorers it must be easier thus if their interplanetary spacecraft generates artificial gravity.

Another question is whether Martian colonists or their children can ever go to Earth. Mars surely has a strong enough gravity to be colonizable but the Earth has more than 2.6 times the surface gravity of Mars so it would be really hard for humans from Mars to adapt to 1 g if they wanted to go to Earth. Their bones would probably be weaker and could breach when exposed to 1 g for too long. Or perhaps they would survive and adapt. We just don't know and perhaps shouldn't try to find out. It wouldn't be risky to live in 1 g rotating space stations instead.

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  • $\begingroup$ the Nautilus-X did not advance past the proposal, the design was completely scrapped in 2011 most parts of it weren't even tested on the iss. $\endgroup$ – Topcode Apr 1 at 18:38
  • $\begingroup$ @Topcode The plans for the ISS test module were scrapped but the Martian spacecraft is still in concept unless the information on it is outdated. $\endgroup$ – user30007 Apr 2 at 5:00
  • $\begingroup$ @uset30007 on wikipedia it says in the status as of 2011 it did not make it past proposal, they are using a different space craft $\endgroup$ – Topcode Apr 2 at 14:38
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    $\begingroup$ @uhoh I wasn't referring to that single mission but to Scott's single stay in space and the other cosmonaut I meant was Valery Polyakov, your list reminded me. $\endgroup$ – user30007 Apr 3 at 7:01
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    $\begingroup$ @uhoh I have to thank YOU! (: $\endgroup$ – user30007 Apr 3 at 7:04

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