If you look at this list of potentially habitable exoplanets, very few of them actually come close to having the same size as Earth, this means most of them would have surfaces gravities significantly different from those on Earth, and mostly likely significantly different atmospheric pressures as well.

For simplicity's sake, let's set aside the issue of whether they need to be terraformed or not, and whether they have native lifeforms.

I'm curious about the problems caused by different gravities:

  1. Are humans resilient enough that they can adapt to those different gravities and gravity won't be an issue?
  2. Will it be necessary to genetically modify humans to be able to survive in those different gravities?
  3. Will we have to create artificial environments to adjust the gravity and the atmosphere for humans and if an exoplanet has a size significantly different than that of earth, then is it inevitable that it will need artificial environments if people are ever going to colonize it?

Which of (1), (2) or (3) is more likely, given current scientific knowledge?

  • $\begingroup$ I don't enough so I'm leaving this as a comment. I think humans should be fine as long as the gravity is less than that of earths and they are able to breath in the same amount of oxygen and CO2 we wouldn't need to worry. Higher Gravity is harder because it will have effects on your internal blood flow and how hard your heart needs to work, so its more of a grey area that I dont think has had any long term testing. $\endgroup$
    – Shadowzee
    Commented Nov 14, 2018 at 22:38
  • $\begingroup$ Short-term, humans can deal with weird gravities just fine (under 3g or so, that is). Long-term, high gravities will wreck their joints / skeletons and low gravities will pose problematic if they ever want to return to 1g $\endgroup$ Commented Nov 14, 2018 at 22:49
  • $\begingroup$ People answering this might want to use the NASA study on long term lack of gravity done by keeping people bed-ridden for months. That's probably the most scientific source of answers we'll come across. $\endgroup$
    – Cort Ammon
    Commented Nov 15, 2018 at 1:36
  • $\begingroup$ You ask 3 closed questions, and then which of the 3 is most likely. $\endgroup$
    – L.Dutch
    Commented Nov 15, 2018 at 6:34
  • $\begingroup$ @Alex Kinman Oh, drat. I just realised that I answered the question based more on the comments that the tags. There could be a second answer sumewhat unfettered by science coming up. Not for many hours, real life and all. $\endgroup$ Commented Nov 15, 2018 at 23:14

2 Answers 2


How hard would it be for humans to colonize an exoplanet with a size significantly different than that of earth (but otherwise suitable for life)?

Let's deal with low-gravity exoplanets first:


Much of the data has been obtained by experiments on people in micro-gravity and zero gravity - so much has to be extrapolated from these data sets.

Short Term Issues:

Kidney stones

"...crew members face an increased risk of developing kidney stones, due to decreased urine output, urine acidity, and increased calcium excretion (a result of bone loss). ................................. Results from this investigation suggest that supplementation with potassium citrate may decrease the risk of renal stone formation..."

So that's perhaps simple to resolve.

Long Term Issues:

Disuse Osteoporosis and Muscle Mass Decrease.

This has been well documented in zero and microgravity studies

Obvious things like Nervous system protection by the skull and spine would make it necessary to maintain a certain degree of bone density.

Whilst Muscle mass and bone density decrease after extended periods in low-gravity could be considered an adaptive function - and may only become an issue if people are going to move between different gravity environments - there are other associated considerations.

Essential Nutrient depletion.

"Between meals, the body maintains a constant concentration of calcium by absorbing it from bone and releasing it into the bloodstream. This constant calcium level in the bloodstream allows proper neural, muscular, and endocrine (hormone) functioning, as well as other cellular activities (e.g., blood clotting).

Bone is also a good source of phosphate, hydrogen, potassium, and magnesium. Like calcium, these minerals are used by many systems of the body for a wide range of purposes.

Less buffer is available during the day if less mineral is present in total, probably making mineral supplements essential.Researchers are currently pursuing multiple lines of research, including hormone level, diet, and exercise."

Known Unknowns:

Vision Changes:

"For example, nine of the 27 astronauts (33 percent) exhibited expansion of the cerebrospinal fluid space surrounding the optic nerve, and six (22 percent) showed flattening of the back of the eyeball, researchers said.

Micro-gravity-induced intracranial hypertension represents a hypothetical risk factor and a potential limitation to long-duration space travel..."

A series of experiments at NASA is designed to test this:

" It is hypothesized that the head-ward fluid shift that occurs ... leads to increased pressure in the brain, which may push on the back of the eye, causing it to change shape.

10.22.18 Results of experiments: Science Results for Everyone Information Pending"

Stiff Arteries, Hypertension, Cardiovascular Disease:

"As humans get older on Earth, arteries stiffen and this causes an increase in blood pressure (hypertension) and elevates the risk for cardiovascular disease. Recently, it has been observed that some crew members returning from the International Space Station (ISS) have much stiffer arteries than when they went into space. The results could provide insight into potential countermeasures to help maintain crew member health, and quality of life for everyone.

10.25.18 Science Results for Everyone Information Pending "

Inflammatory and Oxidative stress.

"The objective of Defining the Relationship Between Biomarkers of Oxidative and Inflammatory Stress and the Risk for Atherosclerosis in Astronauts During and After Long-duration Spaceflight (Cardio Ox) is to determine whether biological markers of oxidative and inflammatory stress are elevated during and after space flight and whether this results in an increased, Ultrasound scans of the carotid and brachial arteries will be obtained at the same time points, as well as through 5 years after landing, as an indicator of cardiovascular health.

10.04.18 Science Results for Everyone Information Pending "

Treatments for many of the above which fall within current medical science's capability.:

Malcolm Cohen, chief of the Human Information Processing Research Branch at NASA Ames:


Cohen has been spinning research subjects in something far more impressive than a carnival ride. He's been studying engineers, mountain climbers, teachers and other paid volunteers as they live for up to 22 hours in a giant, 58-foot diameter centrifuge.

He says:

"...hypergravity could be used to train athletes, providing an environment in which exercises could be conducted with more benefit in shorter time. People who suffer from muscle atrophy might be exposed to it, to stress their muscles more effectively."

"...cardiovascular deconditioning, loss of muscle mass, loss of bone density, and a host of other problems. Artificial gravity could prevent all that -- and centrifuges are one plausible way to generate artificial gravity."

"There are so many options for how best to implement hypergravity most effectively," says Cohen. "Low intensity for long durations, high intensity for short durations, short radius centrifuges ... We know a lot, he says, but there's much more to learn."

Mineral supliments, and vitamin D.

"...some meta-analyses have found a benefit of vitamin D supplements combined with calcium ..."


"Bisphosphonates are useful in decreasing the risk of future fractures in those who have already sustained a fracture due to osteoporosis. Risedronate, Etidronate, Alendronate. Teriparatide (a recombinant parathyroid hormone) has been shown to be effective..."

There are Unknown Unknowns, that we will no doubt have to come to terms with in due time.

It is as yet unclear how effective each treatment would prove and presumably the daily regimen would depend on the specific planetary conditions and would need to be adapted for each individual person's unique physiology.

Any adaptations that the geneticists decided on could be applied on an ongoing basis, with medical science keeping up with any shortfalls.

High Gravity Exoplanets.


The Effect of increasing G:

A hard slap on the face may impose hundreds of g-s locally but may not produce any obvious damage; a constant 15 g-s for a minute .. may be deadly.

NASA Pilots:

They're exposed to hypergravity, too: up to 3.2-g at launch Cohen points out, "fluid weighs more." The heart has to change the way it operates, pumping faster, and working harder to push the blood all the way to the brain. This could cause (..people..) to become dizzy or even, in extreme cases, to pass out.

The relative effect of increased gravity when standing is to increase the blood pressure in the feet and decrease it in the head.

Then when you bend over lowering the position of your head relative to the heart, the blood pressure in your head will shoot up.

Humans can cope with such changes at Earth Gravity, but as Gravity increases, the magnitude of the pressure change also increases.

We might need to make some changes to our Cardio-Vascular system, but how can we decide what?

Think of Giraffes:

Special support structures in the arteries withstand 300/180 millimeters of mercury, preventing them from bursting.As it drops its head down to drink, specialized valves in the neck counter the potentially explosive effects of gravity, blocking blood flowing back into the skull. Meanwhile, a built-in pressure suit in its extraordinarily long legs prevents fluid and blood from pooling in its feet.

Understanding of these remarkable features is still relatively limited. But the giraffe's physiology is a growing area of research for evolutionary biologists and comparative physiologists looking to understand its unique characteristics and apply that knowledge to solving issues in human health.

What about their blood vessels:

Interestingly, the "unnaturally" high blood pressure in giraffes does not culminate in severe vascular lesions, nor does it lead to heart and kidney failure, whereas in humans, the same blood pressure is exceedingly dangerous and will cause severe vascular damage.

Circulatory System:

The 2 feet long heart weighs around 12 kg and is incredibly powerful to pump the blood all the way up its long neck and legs. Moreover, the heart has evolved to have a small radius and thick muscle walls, giving it high power. Also, a series of valves located in the blood vessels that lead up the neck prevent the blood from flowing back to the heart in between beats. The walls of the vessels also thicken as the neck grows longer with age, to avoid rupturing under pressure.

But their legs:

The muscle and skin around the legs fit tightly, increasing the pressure of the blood in the lower body, stopping it draining down. The layer of tight skin on its legs not only maintains pressure but also prevents the vessels from bursting. Furthermore, if the giraffe were to get cuts, this thick skin and inner fascia would prevent blood pooling and excessive bleeding.

What stops them having a Brain Haemorage when they bend down to drink:

Luckily for the giraffe, nature has provided them with a complex pressure-regulation system that controls blood flow. In their brain, there are blood vessels that connect to the convoluted valves or blood sponge in the large neck veins. They are meant specifically to reduce the blood pressure before it enters the brain. Their function is to stop the blood from flowing backward when it dips its head. It is called the Rete mirabile. This amazing organ collects the blood at the skull base and regulates the blood quantity released into the brain. It prevents the head from swelling when it bends over. And it works in reverse as well. When the giraffe quickly lifts its head, the organ stops blood from draining out the brain quickly, saving the animal from fainting.

So, if we adjust our vascular systems to more closely match that of a Giraffe, we could ease our way.

Anabolic Steroids:

As many will have heard from the news, these can help build muscle or bone marrow capacity, or of course building bone density, there are many side effects to be very wary of: infertility, hypogonadism, erectile dysfunction, amenorrhea, rhabdomyolysis - and too many others to list both physical and psychological. Possibly best used sparingly with the best medical evidence in mind only.

Some Usefull Tech:

These could help decrease wear and tear on joints and help support the intra- vertebral disks, stop colonists shrinking and ageing before their time.

Powered Exoskeletons:

"Powered exoskeleton (also known as power armor, powered armor, powered suit, exoframe, hardsuit or exosuit) is a wearable mobile machine that is powered by a system of electric motors, pneumatics, levers, hydraulics, or a combination of technologies that allow for limb movement with increased strength and endurance..."


High g is not comfortable, even with a g-suit.

In older fighter aircraft, 6 g was considered a high level, but with modern fighters 9 g or more can be sustained structurally.

Pilots in Red Bull Air Race World Championship have worn a g-suit called g-Race Suit since the 2009 season. The g-race suit is a liquid (water) filled, autonomous and aircraft independent working full-body g-protection system. It is tailor-made for each pilot and can be fine adjusted via lacings.

The g-race suit contains four so-called "fluid muscles" which are sealed, liquid-filled tubes. Each fluid muscle extends from the shoulder to the ankle. Two fluid muscles – each filled with approximately 1 litre of fluid for a total of around 4 litres (1.1 US gal) per g-race suit – are routed vertically on the front side of the g-race suit and two are routed vertically on the rear side of the g-race suit. The suit weighs on average 6.5 kilograms (14 lb) in total, and its fabric is made out of a special mix of Twaron and Nomex. The counter pressure effect occurs instantaneously without any time delay versus an up to two second delay before reaching full system protection in standard pneumatic, inflatable g-suits. The race pilot utilizes the g-race suit interactively by muscle straining and breathing techniques to achieve an improved cardiac output and thus improved G-protection.

Fluid Baths. (SE Ref above)

The story of John Paul Stappe who in a fluid bath survived a 46.2 g acceleration. Though there is little experimental data except: he broke several bones in the process and it was for just a short period. It may provide comfort and relief in a moderate to high g environment.

Telepresence or Remote Handling:

The Apparatus for Remote Control of Humanoid Robots (ARCHR) is an intuitive teleoperation system for high degree of freedom robots with haptic feedback.

Think The big yellow thing Sigourney Weaver drove in Aliens, but remote controlled from the comfort of your warm salt-water bath.


In short.

There are things we can do to adapt ourselves which are within our capacity now, but insufficient experimental evidence is yet available to be precise about what would be needed under what circumstances - it'd perhaps be wise to park in orbit with the colonists in hypersleep and have a scientific and technical team gather more data, whilst slowly deciding what adaptations to make.

  • $\begingroup$ A lot of the microgravity effects will not happen on a low gravity planet, especially the problems caused by fluid buildup in the upper body. $\endgroup$
    – John
    Commented May 5, 2019 at 21:58

As even the nearest exoplanet is so far away that we will probably have advanced significantly before we attempt an interstellar cruise, genetic or even more radical improvements are very likely to happen.

I would say humans can adapt to gravity between 0.5 and 1.2g or so (pure guess). A surprising wide variety of planets can be in that range - small gas giants if you consider floating in the atmosphere, larger than Earth rocky planets made mostly of very light rocks or water, and obviously the smaller planets.

On a planet with lots of liquid on the surface, we could adapt to any and all gravity, within the limits of where it would be too hot or where the atmosphere creates too much pressure for us. We'd just have to get used to staying in the water or other liquid most of the time.

Lower gravity is no real issue, as we can compensate easily by putting parts of the habitats into centrifuges.

There is a more important issue, though: People able to travel between star systems may not be too interested in deep gravity wells. It's pretty much of a one-way street. So the first interstellar travellers are likely to create outposts on suitable asteroids and moons rather than heavy planets. And some of them will continue on to the next star, so a generation ship would probably continue flying indefinitely (with an advance crew sending some resupply materials into the ship's way and around half the crew leaving at every star).


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