Does lower gravity on Mars make it unsafe and unhealthy for humans?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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.