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Basic Information

A Heavyworlder is the speculative fiction trope of a character or alien creature that grew up on a world with significantly higher gravity than we experience here on Earth. (Generally, this is because their world is much larger than ours, but it could also/instead be a function of their world being made of denser materials than our own. So this sort of character could be from, for example, a super-earth or a brown dwarf.)

The common depiction in science-fiction is a broad-shouldered, very muscular person or species. This usually manifests as some level of superstrength. This often overlaps with the tropes/characterization of the big guy and/or one-man army (and may even be basically dwarves in space!). That's the common, surface-level interpretation, useful because it's easy to grok. And it may well be accurate enough, at least for a world whose gravity is just a fraction higher than the Earth's.

Often though, those depictions aren't really thinking through all the implications of what hypergravity is likely to have on a species' evolution, especially when you're talking about worlds with a much higher gravity than our own. The two-legged upright humanoid form works just great for us Earthlings, but it may not be the direction that natural selection takes in such an environment. For starters, Stamina or Endurance will be at least as likely as Strength to be selected for. Tall gangling creatures such as ourselves are not only an inefficient shape for such a world, but could be downright hazardous since falling is more dangerous on such a world and taller creatures have further to fall if they stumble. The square-cube law tells us that the mass of a creature scales up faster than it's corresponding height or width. So rather than a big hulking brute or tall athletic Adonis, life on a high-gravity world is perhaps more likely to be smaller, and possibly multi-legged with a low center of gravity. Compact reinforced frames with short legs, thick bones, and broad feet (to better distribute weight over more surface-area) may be the pinnacle of life on heavy worlds. They may be really short, is what I'm saying, and probably at least quadruped if not going all the way into being an structured analogous to an earthly centipede, snake or even flatworm.

This is also likely to have psychological and/or territorial impact, as well. If gravity is so strong that the slightest stumble means death, fewer creatures will nest in treetops, or climb mountains. Fear of Heights has the potential to be a racial (or planet-wide) trait. If gravity is cranked up high enough, life may not even decide to crawl up out of the ocean in the first place. It's entirely possible that the only multicellular life on the planet will be in a narrow zone in the upper layers of a body of water — where you're safe from falling hazards — but not deep enough to be crushed under the pressure of having a lot of water weighing down on you.

Pressure is possibly going to be a concern, but is also the sort of thing that life will likely adapt to, to one extent or another. Exoskeletal, crystalline lattices, natural armor or other exotic structures may evolve to increase durability and survivability. Heavyworlders may be silicon-based life that uses ammonia as biological solvent, relying on all that pressure to keep the ammonia liquid. All sorts of bizarre alien biochemistry is possible. They may have a skin, shell or exoskeleton held tight by the pressure, that literally leaks blood when the creature is transplanted to somewhere with lower pressure that doesn't push the interlocking plates together. It's entirely possible that such creatures may be incapable of existing anywhere humans can live, and vice-versa. (If we go to their world, we'd be crushed under our own weight, and if they come to ours they risk explosive decompression or some analog of the bends.)

All of this is likely to have a cultural impact as well as possibly limiting the technological development of any alien life on the planet. Higher gravity means higher escape velocity so any intelligent life there faces much harder hurdles to developing the first airplane, spacecraft, satellite, or space station. They may be highly intelligent and evolved, but assumed reaching the heavens was insurmountable. If life on this world is limited to the surface seas, the technological hurdles start much earlier. It's hard to master fire underwater, and developing electronics is tricky to say the least. You don't need the wheel, it's too wet for paper, and any number of other basic technologies become problematic.

And this is all just assuming the only major difference is the gravity. There will be other evolutionary considerations depending on if the planet they originated from is a gas giant, hot neptune, brown dwarf or just a relatively more mundane super-earth.

Interestingly, if the world has an exceedingly dense atmosphere (which is likely given all that gravity is pretty good at retaining a lot of gas), then atmospheric buoyancy becomes easier to achieve. If the density of the atmosphere is more extreme than the gravity of the planet, you could actually end up with very large flying creatures, that use body shape (and possibly an air bladder) to stay afloat. It's possible such creatures might spend their entire life-cycle in the sky, starting as tiny spores or tadpoles drifting in the breeze, and eventually growing so large that if they were to land they would never be able to achieve flight. So if you had two worlds with similar gravity but different atmospheric composition, one might have only very stout multi-legged land-dwellers in its ecosystem, and the other might be filled with a variety of airborne life. Or you might even find a single world with two ecosystems, a shadow biosphere situation where the armored creatures that lived on the surface were very unlike the hollow-bodied beasts that live their entire lives in upper atmosphere.


1. Non-Fiction Book: The Science of Aliens by Clifford Pickover
4. Documentary Series: Alien Worlds on Netflix. The first episode speculates about airborne life on a high-gravity world.

Game and Story Use

  • Where your game falls on Mohs scale of sci-fi hardness and just how heavy the local gravity is will determine how many of the above traits ought to apply to heavyworlders in your campaign.
  • Will the locals be distrustful of strangers who come from the skies, or will they revere and admire their obviously-dangerous technology?
  • You can have some fun subverting expectations by having a highly intelligent, technologically advanced civilization that is isolated by the extreme gravity making them culturally disinterested in flight and space exploration. PCs put on exo-armor and head down for an away mission only to be surprised by how advanced the locals are in other fields.
  • Here's a fun potential life-cycle: The heavyworlder alien is is amphibious, but has an exoskeleton. Once a year they shed this exoskeleton, but when they do they need to do so in the water, so as to reduce the chance of having their new softer hide crushed by the old one before it strengthens. The water, however, is home to some great predator whose larger size (larger than land creatures that is) can be supported by its buoyancy. Moving on to the land has allowed for technological development and thus the tools to keep the predator at bay.
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