Human bodies are built for Earth's gravity. But what happens if an earthborn human goes up into space—or, a spaceborn human returns to Earth?
Introduction
Satellite by Nick Lake is a daring novel written entirely in "text-speak, but that isn't why it's being highlighted today. Although set in the near future, Satellite poses a genuine problem that current ISS astronauts and future space-dwellers will encounter: the effects of zero gravity on the human body.
In the novel, the protagonist Leo and his friends have spent their entire life in space, having been born inside the space station Moon 2. After touching down on Earth and spending time in its 1G environment, they begin to experience symptoms like blood clots and fatigue.
Musculoskeletal Issues
Human bodies are naturally built to live and walk upright in Earth’s gravity, with thick femurs and strong butt muscles. However, in space, the pull of the Earth is too weak to be felt by those living in space stations, to the point where it's referred to as 0G (the unit of measurement for gravity is 1G=Earth's gravity). The difference in gravity causes the musculoskeletal system to not function properly, as it's adjusted to one environment.
Aboard the ISS, astronauts regularly exercise to prevent muscular atrophy. They run on specially developed treadmills, such as the one below, which allow them to exercise while being locked in place so as to not float away.
Immune System Issues
Another topic worth mentioning is the immune system's response to a new environment. Because the space station Leo lived in was a completely sterile environment, his body hadn't encountered any pathogens that an earthborn would while in the womb. Because of this, he and his friends are locked in a completely sterilized facility for their health. Even after being released from the facility, his body is still prone to infections that would normally be fought off easily by the immune system.
Humans in Space
The implications of a new generation in space are something one must consider when discussing the future of human expansion. If an individual is born and raised in a 0G environment, they would have a difficult time adjusting to on-planet colonies that humans may eventually start. There may be therapies or mechanical supporters developed to help them live in terrestrial environments, but the bodily effects would remain.
Or perhaps the effects of 0G would be embraced by space-living humans. They might slowly evolve over the span of generations, producing a new subspecies of homo sapiens that has also been frequently imagined by scientists and science fiction writers alike: vestigial legs no longer needed to support themselves, with spherical torsos and thinner musculature. Only time will tell, but with SpaceX and other private companies recently branching out into commercial spaceflight, a new era of spacefaring humans may be approaching not so far in the future.
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Other works about living in space:
2001: A Space Odyssey
The Martian
Moon
Passengers
Other resources about living in space, from NASA:
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