Mars' gravity is 38% of that of Earth's.

Supposing a human born and raised on a Mars colony traveled to earth later in their life, would they be able to survive the increased gravity?

For example, I would weigh 63 pounds on Mars, and would land on Earth weighing 166 pounds.


What physiological effects could be expected? If one could not survive, would it be possible through intensive care?

### Some things to consider:

1. Side effects - for example, would one's bones, due to being much thinner, break easily? Would there be respiratory troubles? I suppose there is only speculation in a lot of this as it's never happened.

2. Length of time to full recovery. Obviously, given one survives, the body would eventually adjust, bones thicken, etc. What sort of estimate could one give on how long it would take to adjust and become "normal" on this increased gravity?

• In the Red Mars trilogy, KSR has 2nd and 3rd Generation Martians using Exoskeletons on Earth. – Serban Tanasa Oct 3 '15 at 15:25

You could always simply lie down.

Jokes aside, the answer is that there would be quite a few issues. Your spine would not be used to being so compressed. This is a problem with astronauts returning home from extended stays in space. There are two key issues:

1. Spaceflight osteopenia: In microgravity, there is less stress on the bones in the body. Therefore, they become less dense. Back on Earth, the bones must support weight. However, they are too weak, and it is extremely hard for astronauts to walk again after long stays in space because of this loss. On Mars, a human would have low bone density; they wouldn't be able to stay upright without much effort on Earth. To counteract this, Wikipedia gives the following:

Increasing dietary calcium and vitamin D is a standard countermeasure for osteoporosis. Clay is reportedly used by NASA for retaining calcium.

You'd need a lot of calcium and vitamin D, but it's possible you could adapt to life on Earth.

2. Muscle Atrophy: Something similar happens to muscles. In space, they aren't used to maintaining effort by keeping the body up. Therefore, they become weak. This would also be a problem for someone going from Mars to Earth. Their muscles would only be useful in relatively weak gravity. Wikipedia suggests the following:

One important rehabilitation tool for muscle atrophy includes the use of functional electrical stimulation to stimulate the muscles. This has seen a large amount of success in the rehabilitation of paraplegic patients.

Or you could go the low-tech way and simply work out for a while. It would take quite some time, but it would work.

I think it's safe to say that you would survive, but it would take a lot of effort for you to function normally on Earth.

• Thanks for the excellent answer. I'm trying to get a bit more of a grasp on just how long this would take - a short trip to space vs growing up on 38% gravity would definitely cause more long term effects. Any guess on how many months or years before one would become normal? – dthree Nov 4 '14 at 3:05
• @dc2 I'd like to find stats on how long it takes astronauts to recover; that might help. – HDE 226868 Nov 4 '14 at 3:06
• Very good idea. I'll look around on that. – dthree Nov 4 '14 at 3:09
• @dc2 You might also find this interesting. – HDE 226868 Nov 4 '14 at 3:16
• The heart is also a muscle, so atrophy of the heart would be a major concern. Our Martian might have to remain horizontal at all times for the heart to pump blood to the brain; and could be at risk of a heart attack, especially after exertion. – Royal Canadian Bandit Oct 2 '15 at 8:38

While just going straight from Mars to Earth would be problematic for a native of mars, there is a bigger problem. Currently it would be about 150 day journey to travel between the two planets. if it was all the way in micro-gravity even earthlings will have issues on Mars, though not quite as bad.

So the important thing would be for transportation ships to be built with the ability to have a gravity ring, or even a couple. And everyone would need to exercise and spend some minimum amount of time in these.

It would be even more important for the Mars return to slowly try to acclimate themselves to a heavier gravity, if there was a couple of rings and they could take time working themselves up to full earth they would have several months to adjust before they ever landed on earth. There is a very good chance that they might need most of that time and be pretty pro-active if they don't want to feel like they're being crushed.

Of course the diet on ship should help with the nutrients (calcium, etc) to encourage healthy development.

• Do you think that 150 days on no gravity would have more physical attrition than, say, 30 years of 38% gravity? I am curious to know what the bones of someone who grew up on Mars would look like - and if something that permanent could adjust. – dthree Nov 4 '14 at 16:52
• I'm saying that 150 days with no gravity would be hard on anyone traveling either direction. Broken bones can be mended in less time than that. People can do incredible things with their body if they are serious about it and the trip between planets should be used constructively by all to prepare themselves for the destination. – bowlturner Nov 4 '14 at 16:57