When I first decided to write science fiction, I wondered what was required to sustain human life on another planet? I should start by saying this is a broad-stroke examination of needs. I’m not diving into microbiology or detailed chemistry. What is the base platform requirements for seeking out another Earth-potential planet? I don’t want my characters living in domes. I want another Earth. Below are the requirements for this possibility.
Habitable Zone
The habitable zone is the distance from a planet to the parent star with regard to temperature. NASA calls this the “Goldilocks zone.” Not too hot. Not too cold. In our system, this range includes Venus, Earth, and Mars, with Earth being the only planet in the perfectly ideal range. Venus and Mars are pushing the limits for our comfort, but could be viable with modifications. Jupiter and beyond are simply too cold and dark for anything beyond dome-life. In addition to temperature, solar energy is also required for photosynthesis. If plants are expected to grow, they need light.
Axial Rotation
Finding the Goldilocks Zone is only part of the problem. Our planets also need the ability to spin. Spinning or rotating creates the day/night cycle. While that isn’t absolutely necessary for human sustainment (ask the people surviving in northern Alaska about days spent in complete darkness or sunlight), it certainly helps regulate things like circadian rhythm.
More importantly, rotation helps control surface temperatures. Without spin one side would receive constant sunlight, and the other side complete darkness. The bright side would roast. The dark side would freeze. The planet would have narrow bands suitable for human habitation. This whole temperature imbalance would also create hurricane-grade winds across the planet’s surface. No bueno.
Tidally Locked
When I first started researching habitation on other planets, I encountered an intriguing scenario where two similarly sized planets were locked in a nearby orbit with one another. Unlike the Earth imposing its gravitational will on our much smaller moon, the planets had similar mass. Neither could spin.
I applied this concept to my fictional planet Tykhe. In order to make Tykhe habitable, one of the planets had to be destroyed. This destruction also initiated a highly theoretical slingshot effect that jump started Tykhe’s rotation. But because Tykhe is now orbited by several moons and lots of moon fragments. All these moons create weird gravitational pulls. Tykhe has irregular weather patterns, and the ocean tides are extreme and violent. Tykhe is habitable, but not hospitable, and the oceans are not navigable by ships. If you want friendly oceans, keep the moons small and to a minimum.
The Right Mass
Mass is one of our requirements for gravity. Can humans exist in zero gravity? Yes. Astronauts/Cosmonauts prove this every day aboard the International Space Station. But that isn’t to say it is easy. The human body has become dependent on gravity for proper function. Astronaut Scott Kelly details the struggles in his book Endurance: My Year in Space A Lifetime of Discovery. He says living in space feels like doing a head stand 24/7. There is a weird, constant congestion. Many people feel nauseous. Some astronauts experience issues with a decrease in their vision (particularly when they return to Earth). Blood doesn’t pool or clot in the same way and minor injuries in vacuum can prove fatal. Muscles begin to atrophy. Bone density decreases. Human simply haven’t evolved to zero-g.
On the flip side, too much gravity causes just as many issues. No human could ever visit the surface of Jupiter (for a plethora of reasons). The gravity would crush our delicate frames instantly. Assuming the gravity weren’t that oppressive, humans are still limited by what our bodies could handle. We would gain strength and bone density. That isn’t the biggest problem. Increased gravity will reduce lifespans, and can complicate gestation for pregnancies. Unless we can rapidly modify human anatomy and physiology (which I did in Escher Book I thanks to the wonders of genetic engineering), we won’t be living on any gravity-heavy planets anytime soon.
Magnetosphere
Earth’s magnetic poles are useful beyond orienting a compass. This magnetic field is responsible for containing our atmosphere and deflecting solar radiation. This is one of the biggest obstacles with trying to terraform Mars. The Martian magnetic field is virtually non-existent. Even if we discover viable sources of water and try and jump start an atmosphere, there’s nothing to keep it from dissipating off into space. Forget losing life sustaining gasses. Without an atmosphere, the planet’s surface would be bombarded by deadly solar radiation. Until we can figure out a way to create a magnetosphere, humans will be restricted to EMU suits and dome living. I did read somewhere about the idea of constructing a massive magnetic pole out into space and having it orbit mars like a giant shield. It would deflect solar radiation around the planet. At the very least, it was an interesting theory.
Water
I feel like this goes without stating, but we need water. Plants need water. Animals need water. Not only for drinking, but also the rest of the ecosystem.
In elementary school I learned that oxygen comes from trees and plants. This is true, but we actually receive half of our planet’s oxygen from plankton in the ocean. Oceans are also responsible for affecting our weather systems. Without them, nothing would be the same and the Earth would shrivel up and die. Literally.
Conclusion
I realize I’ve overly simplified some very advanced concepts that will have scientists everywhere cringing. But on a basic level, our 2nd Earth must:
- Exist within the Habitable Zone for the right temperature and light
- Possess axial spin for day/night and temperature control
- Have a suitable gravity
- Posses magnetic poles to contain atmosphere and repel solar radiation
- Have oceans
The more I dive into the recipe, the more I appreciate how absolutely incredible our planet is. Thousands (maybe millions) of factors must align perfectly for us to simply exist. It also saddens me, because I don’t see how humanity will ever figure out a way overcome all the obstacles to terraform Mars. If I had to wager on transforming Mars into a 2nd Earth, or achieving a near-lightspeed capable spacecraft to find another planet somewhere else, my money is on the spaceship. As a species we seem to be pretty good at making things go fast. Not so great at making meaningful moves to take care of the planet (and if you think your battery powered cars are the solution to our environmental crisis–sadly your naivety is just proving my point).
Until we figure out faster than light travel or how to manipulate wormholes, it looks like colonizing another world will live in the realm of fiction. But why not make it believable?