What would a planet where giant creatures live be like? (gravity, weather, etc.)

Question

I am thinking about a planet on which gorilla-like people live in. Gorilla-shaped, walking on their knuckles, but with the capability of complex speech and a slightly more humanoid face (possessing a slight chin and a forehead, still having something more similar to a gorilla teeth structure than a human teeth structure. Their noses are still the silly heart shape and their eyebrow bones being less protruding than a regular gorilla's.)

However, they are huge, reaching about one or two thousand feet (0.3km-0.6km) in height at adulthood.

I assume the land would be entirely untouched since they would live on the necessities and have what we would probably call primitive communities (they are as smart [if not smarter] than humans, they just enjoy the simpler life as they are most likely the strongest thing around if not the biggest).

• I assume low gravity is a must.
• I do know about the infamous square cube law.

Question: What kind of gravity and shape would a planet for giant gorilla-like species have?

Answer 1

They live in a dense planetary ring

In general, a body plan's relation to how much it can scale up in lower gravity is directly proportional to height. So if you assume gorilla like adaptations, but 300 times as tall, then you need 300 times less gravity which is about 0.3% of Earth's gravity. Unfortunately, this indicates something in the gravity range of an asteroid roughly 100km across rather than anything massive enough to be even remotely planet like. Such a celestial body can not hold an atmosphere meaning your giant gorillas must be anaerobic (so you should probably ditch the heart shaped noses all together). Being anaerobic also solves some of the major issues with the oxygen density required for such a large respiratory system.

However, an asterial body this size does not have enough landmass to feed a population of them. A single family of gorillas on Earth needs about 4-30 km² of wilderness or 0.04-0.3 km² of dedicated farmland to survive. If we assume similar scale megaflora, then that means a single family of your aliens needs about 360,000-2,700,000km² of wilderness or 3600-27,000km² of dedicated farmland, but a planet with low enough of gravity for these guys to live would need to have a surface area of about 32,000km² or less. This means that even with advanced agriculture, a planetoid small enough for them to live on would could not support more than about 40-50 of them, and they never would have evolved to be able to get that far.

So, your best bet for these guys is not to stick them on a single planet, but for them to live in a part of space where there are billions of these tiny planetoids that they can jump between. This way, they never experience crippling gravity, but they have access to tons of surface area that they can cultivate thier space veggies on.

It is possible that these creatures started off normal gorilla size when thier moon fell past the Roche limit of the gas giant they were orbiting, but the breakup was slow enough that they, and the plants on thier world had time to evolve. They've all gone super-sized route because this helps the giant animals leap between large rocks that are many km apart, and the large plants that feed them have been selectively bred by the gorillas because the gorillas only transplant flora that are large enough to make for good eating.

Answer 2

You're in dire straits indeed. For starters, such a size may only be explained either by very reduced gravity or through buoyancy.

In the first case, you need to place your space gorillas in a Smoke Ring. I can think of no other environment that would allow them to survive (the necessary low gravity would not allow an atmosphere).

In the other, they would need to live in an ocean on a light planet. Not gorillas, but whales.

The real problem in both cases is their brain. A 300 m leviathan has a neural delay of three seconds using human-like nerve fibers, plus the delay required by peripheral "repeater" brains (one every 15-20 m). Anything above 0.01 g, and they wouldn't be able to break a fall, or avoid a falling weight (something like that is described in Hal Clement's super-heavy planet of Mesklin, whose inhabitants have a phobia of having anything over their head or letting go of weights, since everything falls too fast for them to see).

Perhaps you can solve several of those problems in one fell swoop by having them live in a cold methane or ammonia sea on a cold world. It might be possible to play with fluid viscosity, and they might have such a sensorium, that this would be to them like air is for human beings. Their lives would be then extremely slow compared to a human's, but to them their world would appear like a normal-gravity, normal-speed jungle (exchanging time speed for gravity and living "normally" under a temporal slowdown is calculated and explained in Charles Sheffield's Between the Strokes of Night).

Answer 3

Low Gravity and High Oxygen are musts for such large fauna. However, being that large would require you to just give a fantasy explanation, but you can still do low gravity and high oxygen to help it along.

This is due to the fact that low gravity reduces the effects of the inverse cube law, due to the fact that it reduces weight so it takes longer to be a problem, and high oxygen also allows them to better oxygenate a larger body.

But, again, this wouldn't be able to explain 0.6km tall creatures without some fantasty explanation or handwavium. A scientific answer for beings of that size simply doesn't exist. Unless you have them live underwater, as underwater creatures can grow far larger than land-based ones. That I feel would be able to be a reasonable expanation for their ability to grow so large. This should be helped via lower gravity as I said before. Both really work to reduce the negative effects of large size.

Other issues do arise, such as the propogation of electricity through the nervous system. Nerve signals move at around 120 m/s, so signals would take 5 seconds to reach the end of their body, which would greatly slow their ability to move and respond to stimuli.