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Several science fiction books picture bigger Terran planets with higher gravity. I'm curious to know what would be the maximum gravity mammals similar to the one on earth could survive. Only bones types and structures that exist in our animal world are allowed, no science fiction or magic (no adamantium bones)

A 10G planet seems tough. Elephants can weight up to 5000kg, but if they were smaller, their bones wouldn't be so tough. Therefore if gravity was 10G, I'm not sure whether a 10 times smaller elephant could still exist. Their bones would be too thin and crack under their own weight.

On the other hand, a 2G planet seems ok. Living there would be like constantly carrying a backpack of your own weight. Some very strong humans could probably survive there. We'd have lots of spinal and circulatory problems but eventually our muscles would grow stronger and we would barely cope with such a world.

What do you think would be the limit?

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    $\begingroup$ Would you like information about moving Earth mammals ("In general, if we brought mammals to other planets, how much gravity could they take?") or can we factor in evolution on those planets of mammal-like creatures? $\endgroup$ – Zxyrra Nov 25 '16 at 5:02
  • $\begingroup$ I think that before you face here some serious biological limitations, you'd have a more serious problem. Planet with mass above 10 earths tend to suck nearby hydrogen and turn in to gas giants. On Jupiter "surface" the gravity is technically only 2.5g. $\endgroup$ – Shadow1024 Feb 22 '17 at 17:13
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How much adaptation are you allowing for here? Our existing earth mammals would struggle with increased gravity, and larger ones would struggle more.

If all you are asking about is humans adapting then there is an answer here: Would the human body support living on planets with a greater gravity than Earth?

However in the more general case of life adapting to the conditions I can see life adapting to survive in much greater gravity fields. 10G? No problem. 100G? maybe. What's the limit? We have no idea.

Physical structures would change, bones would be thicker and stronger, creatures would have more legs or at higher gravity levels no legs at all. Mammals shaped like snakes slithering over the surface of a 20G world sounds plausible to me.

Organs would be arranged and function differently, height differences would be minimized (so expect flattened bodies) and nothing would jump or fly. Even small falls are likely to be lethal and climbing extremely hard so most creatures would live on the ground. Burrows and caves would be both dangerous and unlikely so expect small hollows and nests to be the preferred way to live.

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It's easy to work out that 3G would impose serious ( long term fatal) blood pressure issues on an un-adapted human. However, giraffes and dinosaurs show that land animals three or more times our height can develop appropriate adaptation, and so human height in 3G is possible with earthly flesh and blood.

10G is more doubtful. There have never been animals standing 20 meters tall on earth. Animals on such a planet would have to be very squat.

One other speculative thought. In high gravity there could be no trees (assuming Earthlike wood).. Without trees there would be no reason to evolve hands for climbing trees. Without hands, is there a path for intelligence to evolve? It's less of a problem if creatures on a high gravity planet are centauroid: four legs for stability plus two (or more) forelimbs for manipulating their environment.

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