Life in Zero G

Home, home on Lagrange,
Where the space debris always collects,
We possess, so it seems, two of Man's greatest dreams:
Solar power and zero-gee sex.

—William S. Higgens and Barry D. Gehm, The L5 Song

Life, proverbially, finds a way, and a common element in Speculative Biology is imagining how life might respond to profoundly alien environments. Some of the most alien such places are those where one of the most fundamental aspects of life on Earth, gravity, is absent.

This concept is related to that of the Lightworlder, but has notable differences. People living in gravity, low or high, move along a flat surface, with a defined up, down, front and back, and objects still fall universally downwards regardless of how quickly they may do so. By contrast, the world of someone living in zero gravity is in many ways more reminiscent of life underwater; everything exists in a state of buoyancy, floating freely and randomly unless tied down or otherwise secured, and directions are not cleanly distinguished from one another — up, down, left, right, front and back blend into a sphere of free movement. Instead of walking, jumping or even true flying, movement is most akin to swimming through a sea of air. As a consequence, people and animals living in these conditions tend to have appendages shaped like fins, paddles or wings with which to push themselves through the air. Also common are long, spindly limbs, often with prehensile apelike feet, with which to grip onto and climb through three-dimensional environments.

Additionally, the growth of familiar lifeforms is geared to rely on the pull of gravity to orient itself — for instance, plants grow their roots towards the pull of gravity and their stems and leaves away from it. Most forms of plant and animal anatomy are also structured to work in environments where up is one way, down is another, and movement mostly occurs on a two-dimensional plane. Zero-g life is often depicted as growing in rather exotic ways, such as plants that grow leaves and roots at both ends, or out in every direction. Zero-g animals instead tend to have radial symmetry, with limbs and eyes spaced evenly around the axes of their bodies.

Zero-g life can also reach sizes far in excess of what gravity-bound life can manage. Weight and its impact on movement, obviously, are a non-issue. Waste heat is also mitigated by the fact that living things can develop elaborate, delicate cooling fins and filigree-like structures that would collapse in on themselves under gravity. Even the limiting factor of pregnancy is relaxed by expectant mothers not needing to support the physical weight of developing fetuses.

Overlap occurs with Space People. However, most Space People in fiction live in vessels with some form of artificial gravity, and consequently tend to either be Lightworlders or physically identical to real-life people. See also Space Whale, for creatures adapted for life in the void of space.

Note: strictly speaking, there is no such thing as "zero gravity" in a universe in which mass exists somewhere; the proper term would be "microgravity" or "freefall". However, "zero gravity" is the more common term, since that's what media usually thinks that it's depicting.

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Examples:

Fan Works

• Nobledark Imperium: The Voidborn are Space People who have lived on spaceships for millennia, having enduring the fall of the Great and Bountiful Human Dominion and the ensuing dark ages on their fleets. They have long since gotten into the habit of not using artificial gravity on their ships, and have become pale, drawn-out and slender thanks to ages of this lifestyle. When the Tau explorer Por'O M'arc encounters one of their crews during his travels, he wonders to himself whether this will be the fate of his species' Air Caste.

Literature

• Airborn: The third book of the series, Starclimber, focuses on life discovered by the characters in low Earth orbit while on the titular Space Elevator. Unfortunately, that includes a form of 'astral barnacle' that is eating away at the elevator's cable...
• Alien in a Small Town: The Arachne are an alien species who prefer low and zero-G environments. They're all cyborgs who change their bodies as need be, favoring insect- and spider-like shapes to move more easily in gravity-free environments.
• All Tomorrows: The Spacers, humans who went into deep space to escape the Qu, heavily adapted themselves for their new home in giant, zero-G air-filled bubbles, developing extremely spindly limbs and digits for movement in zero-G, as well as pressurized guts and circulatory systems (which allowed them to develop a form of jet propulsion in the bargain). Their descendants, the Asteromorphs, adapt even further to this environment, evolving their legs into paddle-like fins used for steering in the air and developing Super-Intelligence due to gravity no longer constraining the size of their heads and brains.
• At the Mountains of Madness: The Elder Things are depicted as radially symmetrical around their central axis, with tentacles on one end, a ring of eyestalks on the other, and wings running down their sides that they use to fly the luminiferous aether (or sail the solar wind in later interpretations).
• Larry Niven:
  • The Integral Trees: The Smoke Ring is a torus of gas around a star, and exists in an entirely zero-G environment. Its natives have adapted to this environment in a number of ways; they're very tall and thin compared to Earth humans, and have prehensile feet. The Smoke Ring's native life is further adapted for its conditions; notably, all local animals have trilateral symmetry, allowing them to see in a full ring around themselves, while the local humans retain the bilateral symmetry and forward-facing eyes of their terrestrial ancestors.
  • Known Space: The Outsiders appear to have evolved in some kind of asteroid or cometary environments. They are naturally suited for a life in either extremely light gravity at best — even Luna's forgiving pull would kill them, after a while — move by releasing light gas jets form their tentacles' tips, and do not require any kind of atmosphere around themselves. Their ships are elaborate affairs of twisting metal that are mostly exposed to the hard vacuum of interstellar space, and in planetary systems they prefer to lease small, airless moons as waystations.
• Uglies: The "inhumans", the antagonists of the fourth book Extras, are revealed to be Good All Along. They aren't stealing metal to build a weapon, but to build rocketships, hoping to leave Earth, get into orbit, and start farming and establish a society in space to reduce human waste and footprint on Earth. Their bizarre, sometimes terrifying appearances, with prehensile toes and widened eyes, are adaptations made to make life in space easier. They also practice floating in zero-G as much as possible so they can get used to it ahead of time. To do this on Earth, they use hoverball rigs (a common piece of sports equipment in the series' future), setting them to zero-G mode and wearing them 24/7. As a result of the rigs and the body modifications, they've gotten phenomenally good at floating around and using whatever is nearby to propel themselves where they need to go. They call themselves Extraterrestrials, aka, Extras. The heroes support the Extras' endeavor once it's explained to them, and, to make up for the fact that they destroyed a few of the Extras' ships as a result of the misunderstanding, help them recruit, attracting several adventurous people to the project.
• Vorkosigan Saga: Quaddies are a Human Subspecies genetically engineered with an extra set of hands where their legs would normally be and with a number of other genetic modifications to make them capable of surviving indefinitely in microgravity or freefall. They're a former Slave Race rendered surplus to requirements by the invention of Artificial Gravity and fled to a remote asteroid-laden system to escape being sterilized and dumped on a lifeless planet.
• Xeelee Sequence: The inhabitants of the generation ship Nord have slim bodies, arms only a little shorter than legs, and long toes, not as long as fingers but capable of grasping and manipulation — a body built for zero gravity.

Tabletop Games

• Blue Planet: Spacers are a genetically modified subspecies of human designed for life in microgravity. In particular, they not only have Handy Feet but their hips are socketed more like arms. This means that many humans of other subspecies upon seeing a spacer walk in gravity think it looks wrong.
• Eclipse Phase has multiple morphs designed for microgravity, particularly Bouncers, although the basic biomods in most biomorphs and pods counteract the deleterious effects of life without gravity.
• Transhuman Space: The Tennin parahuman was designed by the Duncanites after they got kicked off Mars and fled to the Belt, with many advantages designed to make life easier in microgravity. There's also a variant used by the Wimmin's Pantropic Collective of Margaret Station at L5 that can reproduce by parthenogenesis.

Video Games

• Freespace: The Starfish Alien Shivans are of unknown origins, but are theorized to have somehow evolved in a zero-gravity environment, highlighting how enigmatic and inscrutable they are. Their five limbs have a vaguely radial arrangement (two on top, two on bottom, and one behind), each one ending in a grasping appendage, and appear most suited for grabbing and pushing rather than any standard sort of locomotion.
• Stellaris: Biological species with the "Void Dwellers" trait and the "Habitat" climate preference have evolved to live in artificial space habitats, and therefore suffer large penalties when settled inside gravity wells (i.e. on planets or moons).

Webcomics

• Runaway to the Stars: "Spacer" refers to both a major human space political and cultural bloc and a Genetically Modified Human clade (GMH Spacers) that comprises a large fraction of their population. GMH Spacers have Handy Feet, Prehensile Tails, whiskers to detect air flow, and hirsutism (don't call them monkeys), but they have issues living in Earth-like gravity, with one GMH Spacer character who chose to live planetside needing a back brace to walk upright.

Web Original

• Bosun's Journal:
  • After the destruction of the Nebukadnezar's second habitat cylinder, the Bosun had to halt the third habitat's rotation in order to prevent the now-uneven rotational momentum from tearing the ship apart. This resulted in the habitat becoming a permanently freefall environment, which its inhabitants adapted to by genetically engineering themselves. Their eventually descendants, the weightless people, have slender bodies, arms modified into batlike wings, and long legs with prehensile toes; they live in cities of free-floating buildings tethered to each other and farm groves of floating brambles. Over time, their society decays and they lapse into nonsapience, diversifying into a variety of flying human animals. Some of their descendants eventually make their way to the still-rotating fourth habitat, where most remain in the freefall area immediately around the spin axis. Some becomes stranded on the inner surface, where they somewhat ironically prove to be unsuited for remaining flighted — they simply lack the musculature to achieve liftoff under Earthlike gravity — and evolve into flightless predators.
  • The bird herders are Lilliputians engineered to survive inside a single sealed facility in the ruins of the third habitat, also at zero gravity. They mainly get by using their prehensile feet, as their home has plenty of perches and structures to attach themselves to, and develop the habit of tying bird feathers to their limbs to steer themselves when floating in the air.
  • The custodians, a species very distantly descended from bird herders who regressed into non-sapient gecko-like animals, were transplanted to the third habitat, and redeveloped sapience and civilization over roughly a hundred million years, are much further adapted for zero-G life, with traits such as feet fused into smooth fin-like paddles and bifurcated arms modified to act as a further set of airfins. They spread outwards to the spindles of the other habitats and create enclosed settlements around the ship's outer hull, but largely avoid the rotating surfaces and their centrifugal gravity.
  • Skylords are immense Sky Whales originally descended from livestock created from human genetic material to live in freefall. They eventually evolve into truly massive filter feeders of their habitat's aeroplankton that pass air filled with small animals through a hollow digestive system running right through their bodies, their intestine branching off from the side, and move through a set of long paddles derived from fingers. This highly rarefied body, possible only without the pull of gravity, allows them to reach size nearly ten times that of a blue whale's without dying of overheating.
• Orion's Arm: Freefall habitats aren't uncommon in the Terragen Sphere. For the most part, these consist of non-rotating space stations; freespheres, insulated air-filled bubbles that can be up to thousands of kilometers across; and Niven rings, tori of air around a star usually kept in with some form of solid or nanotech airwall.
  • Human natives of such environments are usually modified to possess flippers, fins or wings, either on their limbs or growing from their sides. "Landscape" features consist mainly of artificially introduced objects and of 0-G-adapted trees, which tend to grow in circular or spherical shapes. Niven rings often partner with Dyson trees, spherical tree-derived plants designed to serve as deep space habitats, which orbit through the gas ring as a way to drop off and pick up passengers and to disperse pollen to be picked up by other trees.
  • Freebirds are birds modified for life in zero gravity — birds adapt to low gravity fairly easily, but they evolved for life in an environment with a definite up and down (for instance, bird wings are vertically asymmetrical in order to generate upwards lift specifically) and need extensive modifications to live in true free fall. Common traits include symmetrical wings to generate life in either direction, shoulder joints capable of figure-eight wing movements, gecko-like feet capable of grasping perches at any angle, additional legs including ones on the "back", and extra eyes for a wider field of vision, and instinctive building of enclosed, egg-like nests instead of the usual cup-shaped ones. More advanced species tend to add traits such as wings modified into circular jellyfish-like "skirts" or rippling tails for propulsion, and often cease to look very much like birds at all.

Western Animation

• Love, Death & Robots: The Swarm in the episode of the same name are an insectoid race that inhabit a nest that drifts through space but contains a breathable atmosphere sealed off from the outside. With only minimal gravity, members of the Swarm (as well as human visitors) get around the nest by to "swimming" through the air.

Real Life

• Several experiments have been conducted on animals in near Earth orbit, but only two have shown signs of adaptation to the environment inside of a space station:
  • In 1973, the eggs of mummichogs (a species of very hardy fish also known as mud minnows) were sent to Skylab. Upon hatching, the fish were able to freely maneuver in microgravity.
  • In 1991, moon jellyfish polyps were sent aboard the ISS to see how they would adapt to microgravity. When they reached adulthood, they swam with little difficulty, but had trouble differentiating up from down on return to Earth.
• Aquatic environments on Earth provide an environment not too dissimilar to zero-g, due to buoyancy counteracting the force of gravity. Owing to this and the Square-Cube Law, the currently known largest living animals are all whales, about an order of magnitude heavier than the heaviest land animals, though some dinosaurs may have given the whales a run for their money.

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