We don’t really think about gravity unless something’s falling or we’re leaving the planet.
But, like many sci-fi worlds before, my Drifting Amalgams universe exists in space and on several different planets. I figured I should study up on gravity’s effects on… well… everything.
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Beyond being the unseen force that governs our movement, gravity has been a notable evolutionary factor.
We know this, in part, because of research done on snakes. In short, organ placement in snakes depends on whether they live primarily in water, stay on land, or climb trees.
Of the three, tree snakes have the closest proximity of heart to brain. Researchers suggest that this is because tree snakes have the most gravitational stress placed on them. Their heart placement allows them to be more gravity tolerant, enduring gravity while traveling up and down regularly.
For humans, too, the way we’ve evolved has been shaped by gravity. Experiments, largely conducted on Earth, show an interesting cellular response for humans in and out of Earth’s gravity.
The Effects of Gravity on Humans
First, it’s important to know that gravity isn’t the only force that impacts cells. Tension and shear stress are also factors. To function properly, cells need to sense all of these forces. Feel a pinch? Cells allow ions to flow–sending the signal that you were pinched–causing you to move your arm. Without the gravity that we’ve evolved in. ions move abnormally. So quick response to the environment in zero gravity can be hampered.
Other systems also struggle in zero gravity. Lack of gravity increases blood retention in the upper body. This increased pressure in the brain inhibits neurotransmitter release. Weightlessness in space causes over 1% bone density loss per month. This is because the cells responsible for building bones are suppressed and the ones for degrading bones are activated. Also, lack of gravity weakens the function of T-cells, a system vital for fighting infection. While exercise and physical training can mitigate some of these effects, these solutions slow down the effects of low gravity but do not halt them.
The Importance of Gravity for Plants
While plant growth also depends on many environmental factors, gravity plays a major role in plant development.
Generally, gravity is a reasonable indicator of up (i.e. the sun) and down (i.e. soil). Accordingly, plants use gravity to orient themselves to best take advantage of photosynthesis, nutrients, and water. When gravity is significantly reduced, plants become much more reliant on moisture and light to understand the world around them.
As with animals, a reduction in gravity can have deleterious effects for plants. Namely, changes in biochemical responses as well as an inability to perform life-sustaining functions like root hydration and gas exchange are common in zero-G environments.
Much research has been advanced towards growing and sustaining plants in space, and there’s no doubt that garden and farm maintenance are a lot of work. Spacecraft with plantlife need to be equipped with special lighting and hydroponics to ensure success.
How Geophysical Structures Affect Gravity
I commonly think of the Earth as a sphere. But this perception isn’t precisely true. It’s much bumpier, thanks to its geographical features like mountain ranges.
Bumpy surfaces mean inconsistent gravitational pull. Essentially, less dense features, like seawater, have less attraction than the rock of mountains. That’s not just true for Earth, it’s just how gravity works. And it’s part of what makes landing spacecraft difficult–especially when smaller objects are involved.
What’s more is that seasonality affects this phenomenon since water shifts, dries, and swells over time; thus, changing the distribution of mass across a planet. While these gravitational shifts are quite small, they are still detectable by satellites, for instance, that accelerate and decelerate when flying over regions with significant changes in density.
Whether talking about physical or geophysical bodies, gravity is an important force for our world and the worlds of our science fiction narratives. Morphology, evolution, and horticulture as well as landing and flight of spaceships–especially small ones–can lend interesting detail to a story that’s written with an understanding of gravity.
Until next time, stay curious.