# Would hypothetical aliens from super-earths be larger and stronger then humans? [closed]

I’m curious how physics would affect the size and strength of human like aliens on super-earth worlds with 1 to 2 times the gravity of earth compared to humans. Would they be similar or be larger or smaller then humans based on the physics of their larger world? Would they need extra muscle mass to survive on super-earths?

• This question might be better suited to SE Biology.
– Fred
Jun 6 at 6:33
• No, not if they evolved in water like squids or returned to water like whales. I think this question may attract answers that are primarily opinion based; there is no way to tell what the right answer is.
– uhoh
Jun 6 at 10:12
• @Fred I think it might be best suited for SE Worldbuilding.
– BMF
Jun 6 at 18:21
• @BMF: It depends on how seriously you take the question. If you want a fantasy type sci fi answer then yes, SE Worldbuilding would be appropriate. But if the question is serious about the potential for life forms on a super Earth type of planet with a higher gravity than Earth, then maybe SE Biology or even SE Physics might be more appropriate.
– Fred
Jun 6 at 21:27
• I’m voting to close this question because it's speculative and not about Space Exploration. Maybe try Worldbuilding. Jun 8 at 8:23

Hypothetical aliens from super-earths would be dwarfs.

The forms of life under larger gravity will evolve smaller. The weight is proportional to the cube of the size, but the muscle strength is only proportional to the cross section area of the muscle, so the square of the size. Small animals are known to be relatively very strong for they weight: ants can lift loads up to 50 times they body weight (source) so potentially should be able to walk over much larger planet. And if they can walk, they probably can live there.

The aliens also need even large relative brain size than humans have, because while body can be smaller, it is not clear if the brain can be much smaller and still support the ability to think as humans do. It would be more evolutionary pressure against the growing brain, meaning that sentient life may have less chances to evolve.

• Not a criticism of this answer, but I wonder how a higher gravity would influence the hydraulic systems of larger lifeforms: blood & the cardiovascular system, capillary vessels, lymph system, liquid filled eyes, cerebral & spinal fluid. Also, would bones be lighter, but stronger; similar to what birds have?
– Fred
Jun 6 at 21:42
• Wouldn't living under water solve all these problems? Also, why not get rid of bones altogether; furry land-squids for example?
– uhoh
Jun 6 at 23:25
• @uhoh: Are you trying to make squids cuddly by giving them fur? Hairy calamari, now there's thought. :-) I think multi colored furry cuttlefish with optically pulsating fur might be cuter & more cuddly.
– Fred
Jun 7 at 4:22
• @Fred I was thinking "primates" but it seems I was on the wrong track. I was thinking that our "octawebbed" friends would need to avoid sweating to stay wet, but it seems that The evolution of hairlessness made way for the emergence of large brains and symbolic thought.
– uhoh
Jun 7 at 4:29

Scaling gives some insights on this question.

The forces on the bones and muscles of a land animal will depend on its weight. Its weight is proportional to its volume times gravitational field, $$g$$. The volume goes as the cube of the linear size of the animal, $$L$$. So the forces go as $$gL^3$$. However, the strength of an animal's bones and muscles depends on their cross-section and tends to go only as the square of the linear size, $$L^2$$. The result is that big animals like elephants have disproprtionately thick legs.

Extending this analysis to varying the gravitational field we find that an elephant on a super earth with twice the gravitational field would be have to be half the linear size for its weight and strength to be correctly proportioned. So animals on a high-g plant might look quite similar but would generally be smaller versions. A half-size elephant (or a half-size human) could quite happily handle a 2g super-earth.

A half-size human would only have one-eighth the brain capacity. That seems a bit worrying. But brain size is not very closely related to intelligence. Sperm whales have brains five times bigger than human brains but we have trouble understanding how intelligent they are. Parrots manage remarkable feats of intelligence with brains one-hundredth the size of ours.

• "...but we have trouble understanding how intelligent they are..." because of our smaller brains of course! :-)
– uhoh
Jun 8 at 12:23