What’s the Maximum Gravity We Could Survive?

By Michael Allen | September 20, 2018 2:13 pm
super earth

The super-Earth Kepler 62f, estimated to be around 40% larger than Earth. (Credit: NASA/Ames/JPL-Caltech)

If we wish to colonize another world, finding a planet with a gravitational field that humans can survive and thrive under will be crucial. If its gravity is too strong our blood will be pulled down into our legs, our bones might break, and we could even be pinned helplessly to the ground.

Finding the gravitational limit of the human body is something that’s better done before we land on a massive new planet. Now, in a paper published on the pre-print server arXiv, three physicists, claim that the maximum gravitational field humans could survive long-term is four-and-a-half times the gravity on Earth.

Or, at least you could if you are an Icelandic strongman – and Game of Thrones monster – who can walk with more than half a metric ton on your back. For mere mortals, the researchers say, it would need to be a little weaker.

Human Limits

To work out the largest gravitational force a human could function in, Nikola Poljak from the University of Zagreb in Croatia, and his colleagues first calculated the compressive strength of a human bone. Based on an average mammal bone, they estimated that a human skeleton could support a gravitational force more than 90 times Earth gravity. But this is its strength when standing still. Once we start running, the stress on our bones – as they flex and bend – increases by a factor of ten. This means we could run on a planet with a gravitational field around ten times that of Earth’s before our bones started to crack.

Skeletal strength is pointless, however, if your muscles aren’t strong enough for you to stand up or walk. Based on squatting ability, Poljak calculated that at five times Earth’s gravity even an elite athlete wouldn’t be able to move from a seated position. For a 110-pound human, that’s the equivalent of squatting around 320 pounds.

For the maximum gravity at which we could take a step, the team turned to Hafþór Júlíus Björnsson, an Icelandic strongman who once walked five steps with a 1430 pound log on his back, smashing a 1,000-year-old record.

Poljak says that Björnsson’s feat is a good comparator because the load on your legs and core muscles in a strong gravitational field feels pretty much like carrying a large weight on your shoulders.

Based on Björnsson’s weight – and the weight of that monster log – Poljak estimates that the strongman would still be able to take a few steps on an exoplanet with a gravitational field around 4.6 times ours.

Björnsson – who you may recognise as Sir Gregor “The Mountain” Clegane from the Game of Thrones TV series – is not, however, the kind of person you see walking down the street every day. He’s 6’9”, weighs in at more than 400 pounds, and in 2018 became the first athlete to win the Arnold Strongman Classic, Europe’s Strongest Man and World’s Strongest Man  competitions in the same year.

Don’t Hold Us Down

Poljak and his colleagues estimate that aiming for an exoplanet with 3 to 4 times Earth’s gravity would be more realistic for an average person – and they would still need rigorous training to get their muscle strength up that of an elite athlete.

Poljak hopes this work will help focus our search for a habitable exoplanet. “Now we know that there is no point in hoping to settle planets with high g-values,” he says.

Many of the rocky exoplanets we’ve found are a good deal bigger than our own planet. Astronomers call them super-Earths. It’s difficult to tell what the gravity on another world is for sure without going there, as density can vary between worlds, but it doesn’t take much to begin adding the pounds. Volume increases as a cube and surface area as a square, so even a slightly bigger planet would have much stronger gravity.

Currently there are 3605 confirmed exoplanets, 594 of which have the known radii and masses needed to determine their gravity. According to Poljak’s calculations, 422 of these have a gravitational field equal to or below 3.5 times Earth’s.

As for ‘strongman’ Björnsson, there are around another 35 exoplanets he could take a few steps on.

CATEGORIZED UNDER: Space & Physics
MORE ABOUT: exoplanets
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  • hisxmark

    Of course, how much a fully developed athlete could endure does not shed much light on how an embryo or child would develop in higher or lower gravity. It does seem that mammalian embryos don’t implant in zero gravity. How human children would develop in scaled gravity is problematic.

    • 7eggert

      It’s more like the male not implanting himself in the female, as far as we know.

      But I wonder how a child would learn to crawl. Maybe one would need to colonize a 1.5 g planet first, then a 2 g planet (etc.). I compare that to living above 5000 m, where no European child can be born and be alive, but the natives could. by genetic adaption.

      • hisxmark

        I seem to recollect that there have been tests in orbit with small mammals, but it was some years ago that I read it.
        And if low gravity would present problems in development, I think it safe to presume that there would be serious problems if the gravity were too great.
        It would be wise to perform research before testing on humans.

        • 7eggert

          I was thinking of these e.g. mice, also it’s yet unclear weather or not tests on humans were done.

      • OWilson

        Our bodies were specifically designed to operate at 1G.

        It would take some eons of evolution, or an artificially created gravity to function in a different gravitational environment.

        Without that, we would be as helpless as a beached whale.

        • Fjgiie Gray

          This is funny. Nobody designed our bodies and no living people can visit a planet 10 light years away. No person can stay alive for more than two thousand years of space travel. No bones left.

          • OWilson

            Some 3.5 billion years of evolution “designed” our bodies!

            Aside from that, I agree. We can forget traveling to other stars.

            In the meantime, we have to be content interpreting and speculating on the light that reaches us from those twinkling lights up there. :)

          • 7eggert

            No*BODY* designed it …

            But call it Nature, call it Evolution, call it God, there is a fundamental force driving the shape and spirit of living beings from one generation to the next.

            The theory of space travel is solved in countless Scifi books. Stopping to think after seeing the first possible difficulty may keep your head from hurting, but then we would not yet have paper and ink nor spears to hunt a mammoth.

          • OWilson

            Ok, I’ll defer to your semantics, lest I get on Politifacts infamous list. :)

            “Figures of speech” are getting a lot of attention these days. While I never claimed a “*BODY* designed the human form. I did use the word design in the generic context of say, butterflies were designed to fly, or eyes were “meant” (by whom?) to see

          • 7eggert

            The part before … was not intended to be the focal point, but to be fun.

          • OWilson

            There’s a smilie for that! :)

            Hugs! :)

  • Alan_McIntire

    The fattest people still walking around weigh about 400 lbs. If the average weight for an adult male was 160 lbs, I’d guess that 2.5 g was about the max, since 160 x 2.5 = 400

  • Mike Richardson

    Life on a world with gravity much higher than Earth standard (1 g) would involve more than just being able to get up or walk. Overweight people dealing with the standard 1 g we all experience on Earth give examples of some of the daily limitations and stresses the human body would endure on a higher gravity planet. While the article deals primarily with short term experiments and the stress placed on bone, living on a world with gravity too much higher than Earth’s would also produce more wear and tear on joints, particularly in the legs and spine, as even walking would be a higher impact activity due to the increased weight. Cardiac enlargement, and potentially early heart failure, would also be a likely consequence of the increased weight on such a world, just as it is a health concern for significantly overweight people on our world.

    Humans can probably adapt to gravity in the 2 to 2.5 g range over time, as muscle mass and bone density can increase to compensate for the extra levels of exertion. Likewise, a healthy person’s heart can enlarge to a certain extent (as frequently is observed in athletes) without harmful effects, so long as the gravity is not placing an extreme burden on the cardiovascular system. If the strain on the human body is not too great, conception and childbirth should also be possible. Children born on a world with twice the Earth’s gravity would likely grow up to be shorter, stronger, and more muscular than people here at home. Their musculoskeletal system (excluding the skull) might more closely resemble that of a stout Neanderthal than what we typically see today.

    From a practical standpoint, gravity of 2-2.5 of Earth standard would also be a good limiting factor for potential colonies based on the constraints of launching and landing spacecraft in a higher gravity well. If gravity is too much higher than Earth’s, the amount of propellant needed to reach orbit or safely decelerate becomes prohibitive (though some form of beamed propulsion system might get around this limit). Likewise, the human body would have to endure even higher g-forces on lift-off and landing. Plus, higher gravity places greater stress on buildings and infrastructure, further complicating matters on the ground.

    All of these concerns may be academic at this point, but if humanity eventually achieves the ability to travel to other stars, they will need to be addressed in much greater detail. I’m just glad to see some thought being given to a future where such things might be possible.

  • Artor

    Of course, standing upright in 2 G’s is enough to make most people pass out as all their blood runs to their feet. Some industrial-strength compression stockings would help, but only a little.

  • Kathleen Drippner

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  • Mike Richardson

    The post I submitted here yesterday was not spam. I would appreciate it being restored here. Thank you.

    • OWilson

      Relax Mikey, you have that Global Warming blog, Imageo, all to yourself, these last couple months! ”

      It’s been purified of all dissent, and all comments, except for yours!

      Trying to moderate this one, too? :)

      • Mike Richardson

        As you well know, your being banned from that blog was a result of your own behavior, and the discretion of the blog’s host, who had been quite tolerant to your off-topic rants to that point. I had nothing to do with that, though given unsolicited comments like the one you’ve provided as an example here, it was probably a good decision.

        But misrepresenting facts is nothing new to you, and your statement is quite ironic if you yourself flagged the comment. It was, to use your words “respectful and topical,” and not cut-and-paste or plagiarized comments, or a personal attack.

        I simply provided a thoughtful contribution to the discussion of gravity and it impacts human beings, here and on hypothetical colony worlds, in my own words. Nothing warranting a block on my post, by most reasonable standards. You, on the other hand, have obligingly demonstrated the type of behavior that has gotten in trouble on multiple occasions. Thank you. Now I think I’ve wasted enough words on you for quite some time, though I’ll be around. 😉

        • OWilson

          Thank you Mikey.

          Rest assured I do not follow you around “flagging your comments”, as the Mods on these blogs can attest.

          Always interesting to hear from you! :)

          Dissenting from the Global Warming alarmism got me and and others banned and threats of banning on Imageo.

          It was not for being disrespectful, according to Tom, it was for posting the “same old stuff”, and he actually went to the trouble of telling me it was just a “time out”!

          Now he has the blog to himself, (and you, of course!) :)

          It’s all on the record, Mikey. The internet never forgets! :)

    • Popcorn Joe

      Would a planet twice the size of Earth with an iron core and with a similar rotation speed, have double the gravity of Earth?

      • Mike Richardson

        Yes, if the density is the same, then you’d have double the mass and double the gravity. However, a planet could have double the surface area of Earth, but have a less dense interior. It could then have less than twice Earth’s gravity. Conversely, a larger core, like Mercury’s, would result in higher density, greater mass, and higher surface gravity. That’s why planetary scientists need both the radius and mass of a world to determine surface gravity.

        • Popcorn Joe

          Thank you much Mike.

          It will be very difficult for NASA to find a livable water world like Earth within reasonable travel distance…

  • Mike Richardson

    In case my initial post was put in limbo due to length, I’m reposting it here in three parts:

    Life on a world with gravity much higher than Earth standard (1 g) would involve more than just being able to get up or walk. Overweight people dealing with the standard 1 g we all experience on Earth give examples of some of the daily limitations and stresses the human body would endure on a higher gravity planet. While the article deals primarily with short term experiments and the stress placed on bone, living on a world with gravity too much higher than Earth’s would also produce more wear and tear on joints, particularly in the legs and spine, as even walking would be a higher impact activity due to the increased weight. Cardiac enlargement, and potentially early heart failure, would also be a likely consequence of the increased weight on such a world, just as it is a health concern for significantly overweight people on our world.

  • Mike Richardson

    Humans can probably adapt to gravity in the 2 to 2.5 g range over time, as muscle mass and bone density can increase to compensate for the extra levels of exertion. Likewise, a healthy person’s heart can enlarge to a certain extent (as frequently is observed in athletes) without harmful effects, so long as the gravity is not placing an extreme burden on the cardiovascular system. If the strain on the human body is not too great, conception and childbirth should also be possible. Children born on a world with twice the Earth’s gravity would likely grow up to be shorter, stronger, and more muscular than people here at home. Their musculoskeletal system (excluding the skull) might more closely resemble that of a stout Neanderthal than what we typically see today.

  • Mike Richardson

    From a practical standpoint, gravity of 2-2.5 of Earth standard would also be a good limiting factor for potential colonies based on the constraints of launching and landing spacecraft in a higher gravity well. If gravity is too much higher than Earth’s, the amount of propellant needed to reach orbit or safely decelerate becomes prohibitive (though some form of beamed propulsion system might get around this limit). Likewise, the human body would have to endure even higher g-forces on lift-off and landing. Plus, higher gravity places greater stress on buildings and infrastructure, further complicating matters on the ground.

    All of these concerns may be academic at this point, but if humanity eventually achieves the ability to travel to other stars, they will need to be addressed in much greater detail. I’m just glad to see some thought being given to a future where such things might be possible.

  • Mike Richardson

    Humans can probably adapt to gravity in the 2 to 2.5 g range over time, as muscle mass and bone density can increase to compensate for the extra levels of exertion. Likewise, a healthy person’s heart can enlarge to a certain extent (as frequently is observed in athletes) without harmful effects, so long as the gravity is not placing an extreme burden on the cardiovascular system. If the strain on the human body is not too great, conception and childbirth should also be possible. Children born on a world with twice the Earth’s gravity would likely grow up to be shorter, stronger, and more muscular than people here at home. Their musculoskeletal system (excluding the skull) might more closely resemble that of a stout Neanderthal than what we typically see today.

  • Mike Richardson

    in case my initial post was put in limbo due to length, here it is in three parts:

    Life on a world with gravity much higher than Earth standard (1 g) would involve more than just being able to get up or walk. Overweight people dealing with the standard 1 g we all experience on Earth give examples of some of the daily limitations and stresses the human body would endure on a higher gravity planet. While the article deals primarily with short term experiments and the stress placed on bone, living on a world with gravity too much higher than Earth’s would also produce more wear and tear on joints, particularly in the legs and spine, as even walking would be a higher impact activity due to the increased weight. Cardiac enlargement, and potentially early heart failure, would also be a likely consequence of the increased weight on such a world, just as it is a health concern for significantly overweight people on our world.

  • https://www.facebook.com/app_scoped_user_id/1439645142730824/ Jamal Molla

    I really appreciate this post. Well described. Thank you so much….

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