2
$\begingroup$

I'm writing a JRPG-inspired novel set on a planet with 1.7 Earth masses and 1.4 Gs, but is it possible for life to even develop on such a high-gravity planet in the first place? I tried scouring the internet for concrete answers, but the only helpful source I can find about this is from Artifexian's video about building terrestrial planets. He claims that the upper limit for planets developing life is 3.5 Earth masses and 1.6 Gs, but I'm not entirely sure if that's correct.

IMPORTANT NOTE: This is not about humans moving from Earth to a high-gravity planet. My story will be mainly a fantasy one taking cues from many Japanese RPGs, where life in-general (including human-like species) have already evolved on the planet in the first place. I just like to use some semblance of realism to avoid falling for fantasy-related pitfalls.

$\endgroup$
  • $\begingroup$ Welcome to World Building SE!. Please visit our tour, it only takes a minute. Also, if you have more time please visit our help center. Interesting question, but I would suggest edit your post and try to make the question more clear, Are you asking if is possible to form life on a planet with that characteristics? $\endgroup$ – Ender Look Jul 29 '18 at 22:59
  • 1
    $\begingroup$ To clarify: you're not talking about life in general, but specifically human(oid) animals? $\endgroup$ – Cadence Jul 29 '18 at 23:17
  • 1
    $\begingroup$ "Life in-general" doesn't mean "which includes a humanoid species". It just means... life. $\endgroup$ – RonJohn Jul 30 '18 at 1:05
  • 1
    $\begingroup$ Possible duplicate of worldbuilding.stackexchange.com/questions/56856/… $\endgroup$ – RonJohn Jul 30 '18 at 1:16
  • 1
    $\begingroup$ I am not familiar with Artifexian and am not interested in combing through YouTube videos for the argumentation. Could you summarize the rationale for why those are the upper-limit values for any form of life to develop? It's a pretty strong statement. $\endgroup$ – Upper_Case Jul 30 '18 at 4:18
3
$\begingroup$

Given that this is for a fantasy novel, I don't see why not.

At 1.0g, a 72.5 kg person weighs 160 lb. At 1.4G, that same person would weigh 224 lb. That's perfectly reasonable: after all, there are a lot of people who are 65 lb overweight, and they get around just fine.

Of course, there will be noticeable differences (bushes, trees, quadrupeds and bipeds, etc) will be shorter, stubbier, stiffer/stronger and won't move as fast, but that's a different question from whether or not life would evolve.

| improve this answer | |
$\endgroup$
2
$\begingroup$

Absolutely.

This is not some incredible feat, as the question seems to assume. It's not clear to me why you're assuming that this would be such an massive challenge.

Consider heavy quadrupeds on Earth, like elephants. They have extra mass compared with humans, and are therefore heavier here, and they exist just fine. So did all of their precursors, and even if less massive they still led to a massive, heavy creature in the Earth environment.

A human on a heavier-G planet would also be heavier, but could exist just fine with physiological adaptations. Thicker bones, heavier muscle, a more squat physique, and so on. There is no reason to think that this is an unrealistic setting for life in general, nor for "humanoid" life (that "-oid" gives a lot of wiggle room already if you really feel like you need it).

If life develops in an environment which can suspend weight (like water, especially anything that would increase buoyancy, like salt water) then the extra gravity is even less of a problem.

It could be the case that the human body plan is less plausible than others in your setting, but that has to do with a lot of factors beyond gravity. Making an exo-planetary species naturally humanoid in form is already a leap in any setting. Compared with that hand-waiving, the gravity factor is practically irrelevant.

| improve this answer | |
$\endgroup$
2
$\begingroup$

What makes humans ("humanoids") human is intelligence. If you sprinkle in sufficient evolutionary advantage for intelligence in your environment, then humanoids vaguely similar to humans could evolve (can they utilize tools, is there reason to plan ahead (seasons: Winter), is there reason to defer gratification (store food)). Now, with a planet with 1.4g, the evolutionary demand for a different body structure supporting the additional constant pressure from gravity, both passively and actively, will be significantly higher. All of that comes at increased resource costs for life to prevail as body size increases. A horse sized ant will not survive a fall 20 times its height (as horses), while a ant sized horse may very well survive that (as ants).

So there is actually some form of threshold to body size. This would imply that the effects of gravity would be roughly comparable for cows at 1.0g and horses at 1.4g. Due to that the body size of these humanoids would evolve to be lower than that of humans, and the muscle mass/density would be higher to better support the graviatational effects. Also it takes much more effort to move.

Well, of course that depends on the environment, other life forms and the time frame. The body size stands in competition with the body sizes of other species - and it has its resource demands, so it's better worth it - evolutionarily speaking. This goes for every trait, including intelligence.

For example it would not be a winning strategy if a species' body size is huge (and presumably immune from predators), while reproduction rate and available food is too low in order to sufficiently reproduce. There is also disease which could bring them down randomly. And if predators still happen to evolve to be able to bring them down (in packs), the size advantage becomes less valuable as well. Such a species would not come into existence in the first place.

| improve this answer | |
$\endgroup$
  • $\begingroup$ Welcome to Worldbuilding, Battle! If you have a moment, please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox (both of which require 5 rep to post on) useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods. Have fun! $\endgroup$ – FoxElemental Jul 30 '18 at 14:48
  • $\begingroup$ Alright, I see what you're getting at. The main problem with higher gravity comes from extra weight, energy management, and the amount of resources needed to survive. Since I don't want any of my characters to be struggling against their own weight and appear slower (which is not ideal for JRPG stories since they always feature nimble and fast characters), I guess I should downgrade my fictional planet so that its gravity is closer to 1 G. I say anywhere between 0.9 G to 1.1 G would be the sweet spot I'm looking for. $\endgroup$ – Sebastien Jul 30 '18 at 16:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.