Humans inhabit almost every corner of our planet. Since the space age began, we’ve gone beyond our planet, traveled in space, and set foot on the moon. It seems inevitable that sometime in the future, humans will be colonizing places other than Earth and living in those places. What challenges face those future colonists?
As a guy who studied Economics in college, I’m no expert in Astronomy. However, I’m a fan of science fiction and of science in general. So my curiosity led me to research the issue and I wanted to share what I learned in hopes that other non-scientists interested in this topic might get something out of it. I hope you find it as fascinating and exciting as I did.
We will look at whether or not humans could live places other than the Earth, and we’ll review everything that must be considered for humans to live in those locations.
First, we’ll take a look at what an environment needs for it to be habitable by humans. Then we’ll discuss how humans could possibly solve the challenges that we are sure to face; challenges that arise from a lack of vital environmental properties that we take for granted here on Earth. We’ll focus on two scenarios: living in space in some type of space station / habitat (which I will refer to as a habitat from here on), and living on the planet Mars. A space habitat and Mars are the two most plausible scenarios. A space habitat is clearly possible because we’ve already created several such as the Mir Space Station and the International Space Station (ISS). We would simply need to apply our resources and manpower to create a space station that people could inhabit for longer periods of time. Among planets, Mars is the most likely planet in our solar system for human colonization for several reasons: Mars is a terrestrial planet, meaning it is made of solid material that we can land on. By contrast, the gas giant planets are made entirely of gas and there is nothing solid to set foot on. The other terrestrial planets, Mercury and Venus, are much too hot for humans to survive. Conversely, Mars has much more hospitable conditions comparable to Earth. Additionally, there are several moons in our solar system (including Earth’s own moon) that could be potential sites for human habitation. For simplicity, we will only discuss Mars, although much of what is true about Mars could apply to some of those moons as well.
So what exactly does a human-friendly environment need?
The things that must be considered are:
- Atmospheric pressure
- Breathable atmosphere
- Water Source
Humans must live in a place that has a significant amount of gravitational pull. Without enough gravity, the bones in the human body start to lose mass and become brittle. In space where there is zero gravity, this is a serious health concern that results in crippling and death. The earth’s gravity has a pull of what is referred to as 1 G. At the time of this writing, the minimum amount of gravity needed to remain healthy is unknown. However, the closer you get to 1 G (Earth’s gravity), the less likely the body will lose bone mass.
However, gravity can’t be too strong or it will crush the human body. It is unknown exactly how much gravitational force a human body can withstand for an extended period of time without negative health effects. Again, the closer it is to 1 G, the less likely the body will be damaged.
Creating artificial gravity in space is simple in concept. All one needs is a circular habitat of the right size which spins. Think of an ant standing on the inside of a bicycle wheel. By keeping the habitat spinning at the correct speed, you could simulate the force of gravity pulling at 1 G, and thereby eliminate the problems caused by weightlessness.
On Mars, things are not so simple. Mars is about half the size of Earth and its gravity is less than half the gravity of Earth’s. There’s not much one can do to change a planet’s gravity. The only question is: would living in Mars’ gravity cause the same bone deterioration that we know arises from living in zero gravity? The answer to that will not be known until humans have actually tried living in that low gravity situation for a long duration.
On Earth, the air that surrounds us presses against our bodies with a force of about 15 pounds per square inch. We don’t feel this load and it poses no problem for our bodies because we evolved under these conditions and our cells push back against the air with their own force. We are unaware of any pressure at all. One can feel a difference in pressure when you dive deep under water; the pressure outside your body is greater than the pressure inside and you feel an overall compression on your lungs, eardrums, and body as a whole. The opposite of that is when you are at a high altitude on a mountain or in an airplane and you feel your eardrums pop due to the air pressure outside your body being less than the pressure inside.
However, when we leave Earth, we encounter environments of different pressures. If the pressure outside of our bodies is too low, our internal pressure has nothing to balance it out. This results in great damage to the body because the pressure in cells and tissue will push to the point of bursting. Imagine taking a really powerful vacuum cleaner and pushing it against your skin. It will painfully damage the area and leave a bruise because the blood vessels burst. In a low pressure environment like outer space, the entire body would be subjected to this but on a much more powerful and more dangerous scale.
If the pressure is too great then the body will be crushed. An example of this can be seen with water pressure: if a human were to go too deep underwater, they would literally be crushed to death by the huge amount of force exerted on their body.
Like gravity, it is unknown exactly how much or how little pressure humans can endure for extended periods of time. However common sense dictates that the closer it is to our pressure here on Earth, the less harmful it will be.
In space, there is no atmosphere to exert pressure so the pressure is zero. On Mars, the pressure is less than 1% the pressure on Earth. In the case of either space or Mars, the pressure is too low for humans to survive. In space, a person would have to be in a pressurized enclosure or a pressurized suit. The same thing is necessary on Mars. However, it is hypothesized that maybe in the future we will be able to terraform Mars. Terraforming is a hypothetical process of making a world hospitable to humans by transforming its natural environment. One proposed method would be to create atmospheric pressure on Mars by adding huge amounts of gas to the atmosphere. At this time we have no way of accomplishing such a feat.
Most people are familiar with the effects of extreme temperatures. If a human body is too hot for too long of a time, it experiences hyperthermia resulting in eventual death. Likewise, if a body is too cold for too long of a time, it experiences hypothermia which also eventually results in death. The human body can only survive in a relatively narrow range of temperatures. The temperatures that we experience here on Earth vary greatly but are mild when compared with the freezing or burning temperatures found in other parts of the solar system. Venus, for example, is a scorching 894 °F (480 °C). Pluto on the other hand is a frigid -380 °F (-229 °C)
In space a person would have to be in an enclosure which could have its temperature regulated by common heating methods such as solar or electric heating. On Mars the temperature ranges from as low as -220 °F (-140 °C) to as high as 68 °F (20 °C). While this is certainly cold, Mars at its warmest can be relatively close to temperatures that can be found here on Earth. Assuming all other factors could be ignored, clothing to insulate the human body and keep it warm could be developed without too much complexity. Humans have plenty of experience protecting themselves from cold temperatures here on Earth.
The sun gives off a wide spectrum of radiation: from the visible light that allows us to see, to the infrared radiation that gives us heat, to the ultraviolet radiation responsible for sunburns and skin cancer. Many people are aware of the long-term dangers of exposure to too much sunlight (skin cancer). The part of the sun’s rays that cause skin cancer is the ultraviolet (UV) radiation. But here on Earth, we only get a tiny fraction of the total radiation emitted from the sun. That is because we are protected by the earth’s magnetic field and the atmosphere to a certain extent. The universe is filled with dangerous radiation that emanates not only from the sun but from everywhere in the cosmos. The earth has a giant magnetic field that deflects dangerous radiation from the sun and other parts of the universe. But a human that is not on Earth (e.g. in space) is not protected by Earth’s magnetic field and is therefore exposed to high levels of this radiation, which can cause death from the radiation itself or can lead to long term consequences like cancer. Minimizing the exposure to this radiation can present a real challenge because it can pass through objects such as the walls of a spacecraft.
Radiation is a difficult problem to deal with because without protection from Earth’s magnetic field, the radiation permeates just about every corner of our solar system. In space, the habitat would have to be lined with extra thick shielding of the right material which will add substantial mass to the habitat. This poses a problem because the more massive a spacecraft is, the more energy it takes to launch it, maneuver it, land it, etc.
Unfortunately for humans, Mars has no magnetic field like the Earth’s that deflects harmful radiation. On Mars however, we could build thick-walled bunkers that shield against radiation. Similarly, we could burrow into Mars’ surface and build underground habitats. A thick layer of Mars soil above the habitat would offer sufficient protection. Sadly, spending too much time outside these structures would result in absorbing dangerous amounts of radiation.
Humans need to breathe gas that contains a significant quantity of oxygen. The air we breathe here on Earth contains 20% oxygen; the rest is mostly nitrogen which is an inert, non-reacting, non-toxic gas. Note that an atmosphere may exert the proper amount of pressure for humans but might consist of gases that are not breathable. In that case the oxygen must be supplied via other means such as a scuba diving breathing device.
If humans are in an enclosure, it could obviously be filled with the appropriate mixture of gases (e.g. oxygen). We currently have the technology to turn water into breathable oxygen via a process called electrolysis where electricity is used to split water molecules into hydrogen gas and oxygen gas. The oxygen can then be used to breathe. . We also have the technology to remove carbon dioxide from the air. Both of these examples of technology are currently used in the ISS (the International Space Station). Outside an enclosure, a simple breathing device could suffice. For example, if all other factors were hospitable to humans such as a comfortable temperate and pressure, but the atmosphere contained gases that were not breathable, simply using a scuba-like breathing device would allow a person to survive.
The degree to how necessary sunlight is for humans is not as clear cut as the previous factors. Humans can live without sunlight, but some evidence has emerged showing the detrimental effects of lack of sunlight such as problems with mental health. Sunlight can also be used to grow food and sunlight provides a source of power by using solar panels.
Again, it is possible for humans to survive without sunlight and in certain instances they might have to such as if they were living underground on Mars. In a situation such as that, artificial lighting that mimics sunlight could be used in the same way it’s used for conditions such as Seasonal Affective Disorder, a type of depression that is thought to result from a lack of sunlight and is more prevalent in areas that get less sun during part of the year such as Alaska. Additionally, we have the ability to use artificial lighting to grow crops indoors and we could do so in the absence of sunlight. Sunlight will usually be available to power solar panels, but in some instances it might be necessary to have a nuclear reactor to provide power in addition to or in place of solar power. Nuclear reactors are very efficient sources of energy that require only a tiny amount of fuel to provide large amounts of power for a long period of time. In a space habitat this would add a huge amount of mass since nuclear reactors are heavy. That would not pose a problem on Mars.
Water is crucial. It is needed for human consumption, bathing, watering any crops that might be present, consumption by any animals that might be present, and it is used to cool nuclear reactors. Water is also needed to create breathable oxygen. But water is heavy and therefore requires a lot of fuel to transport it in space, so it is crucial to carefully utilize every drop.
Water reclamation and purification technology currently in use aboard the ISS allows most water to be reused. However, the tiny amount of water lost adds up over time and a space habitat would have to eventually be resupplied with water from an external source. This poses a problem if the habitat is far away. On Mars, that resupply could come from mining the frozen water ice and melting it to create liquid water.
An obvious but important requirement is food. Humans in space or on Mars will need enough food to eat to be able to survive for a long time. Animal and plant sources of food would have to be obtained in new and innovative ways.
The primary method for providing food would have to be growing crops. This could be accomplished via direct sunlight or with artificial growing lights. The environment would need to be set up to allow plants to grow, including the proper pressure, temperature, and nutrient requirements. In addition, low maintenance animals such as fish could be cultivated for food.
Humans are relatively fragile creatures that can only survive in a narrow range of conditions. Conversely, humans are remarkably adaptable and our technology grows at a phenomenal rate. The challenges of living in places other than Earth are significant but there are some current solutions to these hurdles and other solutions that will become more viable in the future. At this point, humankind has the ability to live in space and on other worlds such as Mars, albeit in a rather enclosed space. Whether we currently have the resources to implement these ideas is another question. However, none of these obstacles seem completely insurmountable and it’s only a matter of time before humans can call another world “home.”