Can We Live on Mars?
Stephen Hawking once said that humans must colonise other planets within 100 years or face extinction. His fears included pandemics, climate change, nuclear war, artificial intelligence, or asteroid impacts wiping civilisation off the face of Earth.
With these catastrophic threats hanging over us, our security as a species falls to colonising other planets and moons. The 100-year timeframe may be alarmist—but then again, things are really hotting up for humanity. And there's everything at stake.
It's no secret that Elon Musk wants to colonise Mars as a backup home for humanity. But how likely is it that we'll see cities on Mars in our lifetime? Is it even possible to terraform and colonise other planets with the science we have today?
Life on Earth evolved over billions of years under specific environmental conditions including temperature, pressure, and gravity. Even if it were possible for humans to biologically adapt to live on Mars, it would take us vast evolutionary timeframes to do so.
The solution is to adapt Mars to our bodies instead. And this is where the biggest challenges lie—because in several critical ways, Mars is very different from Earth.
In the 1940s, the science fiction author, Jack Williamson, gave us the term terraforming (literally Earth-shaping). It describes how we might modify the atmosphere, ecology, and surface topography of other planets to make them habitable to humans.
In reality, such a challenge is immense—many orders of magnitude greater than restoring our own runaway climate change. And yet, some star-gazing scientists are conceptualising ways we could terraform Mars on the basis that we must start somewhere.
"Who can doubt that if the first steps are taken, that the developments required to complete the job will not follow, for what is ultimately at stake is an infinite universe of habitable worlds." - Zubrin and McKay, Technological Requirements for Terraforming Mars
The first major challenge of terraforming Mars is to raise the temperature. Mars is further from the Sun, receiving 40% less light and heat than Earth. What's more, without a magnetic field, the thin atmosphere continually leaks out into space. This makes Mars extremely cold, with an average temperature of -63°C (-81°F).
So how do you warm a planet? Ironically, we already know one way. Humans have inadvertently warmed Earth by 1°C as a by-product of industrialisation. So we might build giant factories on Mars specifically to pump out halocarbon gases and create a greenhouse effect.
"[Power requirements are] on the order of 1000 MWe, and the required timescale for climate and atmosphere modification is on the order of 50 years." - Zubrin and McKay, Technological Requirements for Terraforming Mars
Another solution is to place massive orbital mirrors around Mars. They'd need to be enormous—some 100km wide and weighing 200,000 tonnes—and produced in space out of asteroid or moon material. When angled to reflect sunlight onto Mars' south pole, they could melt vast amounts of frozen carbon dioxide which would thicken the atmosphere.
Once Mars is warm enough, it could support photosynthetic bacteria which would introduce more oxygen into the atmosphere. Not only would an active biosphere make the air breathable, but it would offer a self-sustaining buffer against solar winds carrying destructive high energy radiation.
However, this is all conceptual. The reality of terraforming Mars presents huge technological challenges, let alone the inherent physical limitations we may never overcome.
For instance, we may be stymied by the maximum air pressure we could induce by thickening the atmosphere. Currently, the pressure on Mars is 6.5 millibars; a fraction of our 1,013 millibars at sea level.
The lowest possible pressure for human survival is 62 millibars. Below this level, blood boils at body temperature.
There's also fierce debate over the potential for meaningful oceans on Mars. Geological evidence suggests that rivers once flowed on the red planet, collecting in pools, lakes, and perhaps small oceans. Over time, the water became trapped in the planet's crust or escaped into space due to insufficient gravity.
But it's hard to quantify the size of these lost reservoirs based on remote sensing and rover studies alone. Computer models produce conflicting data, while some argue that Mars is simply too small to retain significant surface water.
"There is a very limited size range for planets to have just enough but not too much water to develop a habitable surface environment." - Klaus Mezger, Center for Space and Habitability
Mars may never be like the blue marble of Earth. If so, human colonies may forever rely on artificial habitats and life support; a permanent risk factor that undermines Hawking's vision of extraterrestrial colonies with strong chances of survival off-Earth.
Yet this hasn't put off SpaceX, which is gearing up for a crewed mission to Mars this decade. Likewise, numerous public and private agencies (including NASA, ESA, Roscosmos, ISRO, CNSA, Lockheed Martin, and Boeing) are also looking to seed the alien planet with life.
How to Get to Mars
In the upcoming 2028-29 launch window, SpaceX will send humans to Mars to establish mining, power, and life support infrastructure. Just how fraught is this mission?
The moment we leave the protective shroud of the Earth's atmosphere and magnetic field, conditions in space become pretty inhospitable. The Mars-bound Starship must be equipped to overcome challenges as diverse as space debris ripping through the hull, to the safe disposal of passenger poo.
The shortest journey time to Mars is about six months, though it's usually longer due to the independent orbits of the planets. On close approach roughly every two years, Earth and Mars are 62 million km apart, while the average straight line distance at any time is 225 million km.
On the journey to Mars, communication with Earth will be delayed by 3-22 minutes, such that astronauts will need to resolve emergencies without technical support.
Even when the trip goes to plan, space travel puts considerable strain on the human body. In zero gravity aboard the Starship, travellers will lose bone density at a rate of 1% per month. This isn't be a problem in the low gravity environment of Mars, but would be a serious issue on their return to Earth.
Astronauts aboard the International Space Station perform 2.5 hours of exercise every day just to maintain their baseline bone and muscle strength on Earth.
We must also consider the psychological stress and isolation of space travel. Alien taught us that in space, no-one can hear you scream. However, your fellow Starship passengers may beg to differ, politely requesting you keep your psychosis to yourself.
In short, the journey to Mars is technically viable. But it comes with a stack of risks, and not all humans are cut out for it.
Can We Live on Mars?
So the first humans arrive on Mars. What will it be like to live on the alien planet?
In one sense, it'll be very boring. This was shown by volunteers who spent a full year in a fake Martian habitat on a mountain in Hawaii. Time dragged. Relationships got messy. People back home died. Still, the six volunteers held out to the end, showing remarkable resilience in the face of a highly restricted lifestyle.
On the upside, there will be plenty of work to do. These passionate space-farers will be tasked with building complex life support systems. One of these will include high efficiency water processing. And while the ISS has demonstrated that around 70% of water can be recycled, early colonists will be keen to access frozen water on-site by drilling on Mars.
If successful, the decades that follow could see mass migration to drive construction of the first Mars city. Elon Musk predicts that 100 Starships, each capable of carrying 100 people, could leave Earth at every launch window. At this rate, 10,000 people might arrive on Mars every two years.
But life on Mars will be precarious. Even with terraforming underway, colonists will be up against enormous challenges inherent to the environment.
- Lower Gravity. While Mars is about half the size of Earth, it has just 10% of the mass. This makes gravity around 38% of that Earth. An 80kg adult on Earth will feel about 30kg on Mars, while their bones and muscles will degrade to match the new environment. If they plan to return to Earth, they'll have to stick to rigorous exercise routines and/or undergo physiotherapy later.
- Longer Days. Mars takes almost twice as long as Earth to orbit the Sun, with a year lasting 667 Martian days. But it's the day-night cycle that poses problems. The 24 hours and 40 minutes of each day will impact cumulatively on circadian rhythms, triggering long-term sleep disruption, mood changes, and insomnia.
- Lack of Oxygen. Shout out for people who enjoy breathing. The atmosphere on Mars is 95% carbon dioxide (vs Earth's 0.04%) and 0.1% oxygen (vs Earth's 21%). To maintain breathable habitats, colonists will rely on technology like MOXIE, a device developed by NASA and the ESA that continually extracts oxygen from the carbon dioxide-rich air. Like permanent ICU patients, Martians will be completely dependent on technology to keep them alive.
- Dust Storms. These are a serious threat to solar power supply. Mars is made chiefly of iron-rich rock, which produces copious red dust and the largest dust storms ever observed in our solar system. These storms can rage for months, sometimes covering the whole planet, and will render solar panels useless. Alternate energy sources will be critical.
- Colder Temperatures. On Mars, the Sun appears half its normal size, and delivering much less light and heat. But it's the thin atmosphere that really keeps Mars cool. Heat and moisture are lost to space, while UV radiation is high. The average temperature on Mars is -63°C (-81°F) compared to Earth's 14°C (57°F). Summer at the equator sees daytime highs of 20°C (68°F) but this drops to -73°C (-99°F) at night. Indoor heating will be essential.
- Giant Volcanoes. Let's not forget about Olympus Mons, an active volcano on Mars that dwarfs our greatest mountains. Being a shield volcano with gently sloping sides, you can't see its entire profile from the ground, even from a distance. Olympus Mons is so big that it curves visibly around the planet.
While it's often said that Mars is similar to Earth, this is only relative to other alien worlds. In practical terms, being able to live on Mars poses enormous challenges, some of which are dramatised in the National Geographic series Mars. Besides the major considerations listed here, it highlights a host of biological, psychological, and political hazards of colonising Mars.
Colonising The Solar System
Can we live elsewhere in our solar system? Beyond Earth and Mars, there are still six more planets and 180 moons we might evaluate as alternative human habitats.
- Mercury is a Hot Mess. Mercury orbits closest to the Sun at just 58 million km, which makes the surface heat and radiation extremely intense. Temperatures reach 426°C (800°F) by day and -173°C (-280°F) by night. Even a lead-based sunblock would melt off your face.
- Venus is Another Hell Ball. Venus orbits further out from the Sun at 108 million km but is still far too hot for us to handle. Day or night, north or south, surface temperatures are an even fiercer 460°C (860°F) due to the thick carbon dioxide atmosphere.
- Jupiter Would Crush Us. Jupiter is the largest planet in our solar system with a mass 2.5 times greater than all the other planets combined. Its atmosphere is so thick it literally crushes our probes with its pressure. We do know, however, that beneath the dense atmosphere, Jupiter becomes liquid and then solid, with pressures 50-100 million times stronger than at our sea level.
Jupiter has a funny way of spinning, moving faster at the equator than at the poles. It also has the fastest rotational speed in the solar system, producing 10-hour days and winds of 480km/h (300mph).
Jupiter's Great Red Spot is a never-ending storm, first sighted in the 17th century. The storm is more than twice the size of Earth and marks an area of super high pressure.
All in all, Jupiter looks pretty inhospitable. But it also has 69 moons, the most famous of which are Europa and Callisto.
- Europa is a Smooth Ice Moon. Photos of Europa show a smooth icy surface, devoid of craters due to ocean currents continually recycling the ice. The moon is -160°C (-256°F) at the equator and -220°C (-364°F) at the poles. It;s prone to ice quakes and violent water plumes exploding through the surface. The same side of Europa always faces Jupiter, and with no atmosphere, it's continually bombarded with deadly radiation. And yet the ocean beneath the ice could harbour aliens. NASA is mulling over number of exploration vehicles including the amphibious squid rover to find out if there's already life on Europa.
- Callisto is a Cratered Ice Moon. Callisto is famous for being the most heavily cratered object in our solar system. The lack of weather and geological activity means that ancient craters never disappear, and yet, the ocean beneath the ice could also support cold-tolerant life forms. This is a major enticement to set up base camp on the surface.
The Search for Earth-Like Exoplanets
As we look around our solar system, Mars once again looks pretty decent. But this is just our local neighbourhood. Space telescopes like the Kepler Space Observatory and the James Webb Space Telescope allow researchers to not only detect the presence of these rocky exoplanets, but to map their atmospheres too.
Most exoplanets can only be observed indirectly because they're so far away. When an exoplanet passes in front, or even behind, its host star, the transit creates a change in solar luminescence. This provides the tell-tale sign of an exoplanet in orbit.
Analysis of the different wavelengths of light provides information on the atmospheric composition of the exoplanet, including water, temperature, and clouds.
More than 4,000 exoplanets have been confirmed so far, prompting the estimate of 300 million Earth-size planets in the habitable zone of sun-like stars across the Milky Way.
The closest exoplanet to Earth is Proxima Centauri b, some four light-years away. While it has a viable mass of about 1.3 times that of Earth, it orbits terribly close to its parent star, exposing it to extreme ultraviolet radiation.
Our prime candidate for an Earth-like planet is Kepler-186f, some 490 light years away.
If that sounds close—it isn't. If we consider that our fastest space probe would take 20,000 years to travel one light-year, then our best planetary candidate has a journey time of almost 10 million years. In making the journey, the species to arrive on Kepler-186f would heartbreakingly different from the ancestral species that departed Earth.
Perhaps future technology will solve this problem. The laws of physics say we'll never travel at the speed of light, but what of teleportation?
Though there are technical challenges to overcome, the theoretical physicist, Michio Kaku, says that human teleportation may be possible within 100 years. He imagines a machine like an ultra high resolution MRI scanner that transmits us as data, atom by atom.
As we contemplate our future as a multiplanetary species, some fear that it equates to giving up on Earth. After all, we've mined our home planet for natural resources, crashed its biodiversity, and primed it for climate ruin. Does colonising Mars make Earth a disposable planet?
Despite the tragedy of these facts, expanding to Mars will not render Earth obsolete to humanity. Earth would far sooner ditch us. In 50,000 years, the next glacial period will ravage the land, creating catastrophic cooling and extinctions. It will last for 90,000 years. Humanity itself may not survive.
The third rock from the Sun will survive long after we're gone. Indeed, by today's standards, Earth could be better off for it.
Humans are a mere blip on the geological timeline. As a civilisation capable of self-preservation, we're morally obligated to hedge our bets. Establishing discrete colonies on moons and other planets will distribute the eggs of humanity across many baskets, so that one catastrophic basket loss won't commit our species to extinction.
"You want to wake up in the morning and think the future is going to be great—and that's what being a spacefaring civilization is all about." - Elon Musk