Will orchids ever bloom on Mars? The realities of colonizing the Red Planet

Our vision of colonizing Mars is heavily influenced by the blockbuster sci-fi movie Total Recall. A domed city on the red planet, bustling with life and adventure — what’s not to love? Yet, creating a fantasy in the confines of a Hollywood studio is much easier than transforming a barren rock into a second home for humans. The engineering challenges of this endeavor will far exceed the scope of a romantic space adventure. No matter how advanced technology becomes, every Martian will still face a down-to-earth problem: what's for dinner? On Martian terrain, even the modest task of growing home potatoes can escalate into a challenge of epic proportions.

Fig. 1 Plants that thrive on Earth can't survive in toxic martian soil, blasted by radiation.

Martian soil is infertile and toxic

Martian soil is a sterile regolith, the rock crushed into gravel and dust over billions of years due to meteoroid bombardment and erosion. Laced with chemicals so toxic that they would kill most plants, it would have to be thoroughly washed before anything could grow. On Earth, this would be simple. On Mars, there’s no liquid water. Colonists would have to extract ice buried beneath the surface, melt and purify it, and then use this precious resource to rinse tons of soil, recovering every drop in the process. It's not exactly your average weekend at the allotment.

Healthy soil on Earth teems with life, full of microbes, fungi, worms, and decaying organic matter. This ecosystem supplies nutrients for plant growth. In contrast, Martian regolith is completely sterile, meeting the scientific definition of "no signs of life." To breathe life into this dead soil, colonists would need to import large quantities of organic matter to prepare the soil for future agriculture. In the solar system, where all planets are as lifeless as Mars apart from Earth, the organic matter could only come from us. Therefore, every ounce of organic stuff that Mars would gain must be the ounce that our planet lost forever.

Transporting food and agricultural equipment to Mars presents challenges far beyond those of a typical home delivery. With a distance of approximately 225 million km (140 million miles) between Mars and Earth, the fuel costs will be exceptionally high. Moving just 1 kg of material demands about 120 kg of propellant. This is merely the start. When you factor in additional costs, we can only hope that these high prices won't dampen the appetite of Martian settlers.

Martian radiation and climate

Mars' atmosphere is nearly 100 times thinner than Earth's, and consists primarily of carbon dioxide, which plants love and humans hate. However, the thin atmosphere and lack of a magnetic field leave Mars vulnerable to harmful cosmic rays and solar radiation. This exposure could cause severe radiation burns, acute radiation sickness, and an increased risk of cancer in unprotected humans. Plants are even more vulnerable to intense ultraviolet radiation, which would bleach them of chlorophyll, causing them to wilt and die within days. All life forms, including humans, animals, and plants, would require constant protection, posing one of the biggest engineering challenges.

Fig. 2 Artist's impression of a prospective human colony on Mars. Credit: NASA

Building underground living spaces and greenhouses is the most cost-efficient choice. By going just 1-2 meters beneath the regolith, radiation can be reduced to Earth levels. However, not everyone would fancy being buried under regolith without windows and natural light. Plants require sunlight to convert the planet's carbon dioxide into oxygen and organic matter through photosynthesis. This prompts designers to explore alternative solutions, such as creating domes on the surface with specialized glass for windows (Fig. 2). In greenhouses, more economical polystyrene panels, similar to those used on Earth, but with an added anti-UV film, could be employed.

The challenges extend beyond construction. Being farther from the Sun, Mars will subject the settlers to freezing temperatures of –60 °C (–76 °F) on average, with milder summer spells on the equator for some relief. While on Earth, we often grumble about rain and seek shelter under umbrellas, on Mars, rain doesn’t exist. Instead, the dry atmosphere fuels massive dust storms that can last for weeks, casting the planet into a dim, sunless haze. An umbrella won't protect you from regolith dust, though it wouldn't be necessary. Colonists will always need to wear spacesuits outdoors, and crops will grow in the pressurized greenhouses with Earth-like temperature and humidity.

Robots come first

Due to significant risks, all initial preparations will be conducted by robots. This is not just safer, but actually cheaper. Before humans arrive, robotic pioneers will excavate regolith to lay foundations and assemble dome living structures, power stations, and landing pads for supply deliveries. To transform the harsh environment into a human-friendly habitat, they will establish water extraction systems and start generating oxygen from the Martian atmosphere using already developed technologies. Soil preparation will ensue with washing regolith using recycled water, mixing in organic matter shipped from Earth, and testing the first crop grown in sealed greenhouses.

Fig. 3. The Perseverance rover during its landing on the Martian surface, being lowered by a rocket-powered descent stage. This moment represents the final phase of the Entry, Descent, and Landing sequence, often referred to by engineers as the “seven minutes of terror.” Image credit: NASA/JPL-Caltech

Current robotic missions have performed sample drilling of the Martian regolith to examine its characteristics. New excavation systems would need to be developed, capable of operating on the alien soil in low gravity. Martian rigolith differs from Earth's soil in density, cohesion, and ice content, presenting extra challenges for excavating systems. In low gravity, machinery's stability is affected, and the coordination between moving parts becomes more complex. Much preparation work is still required before the groundwork begins. For now, the large-scale excavations remain a future goal rather than a present reality. Yet, Mars colonization is an active project, not science fiction, in which several governmental, private, and academic organizations are involved.

No petals in spring, only a roar of Martian geysers

Mars takes approximately 687 Earth days to complete its orbit around the Sun, resulting in seasons that last nearly twice as long as those on Earth. If Mars had a climate similar to ours, Martian colonists could enjoy the sight of blooming orchids for twice as long. However, the freezing temperatures rule out any dreams of seeing red terrains covered with vibrant flowers. Instead, in spring, Mars would offer colonists a different treat, a natural wonder as unique to Mars as orchids are to Earth: spectacular carbon dioxide geysers, blasting jets of dust up to 100 meters (330 feet) into the air.

Fig. 3. Martian carbon dioxide geysers, photographed from a Martian satellite. Credit: NASA/JPL-Caltech/University of Arizona

 In spring,  the intensified sunlight reaches a translucent layer of dry ice at the poles, warming the ground beneath it. This process causes the CO₂ ice at the bottom to sublime into gas, with pressure building up until the gas erupts into jets (Fig. 3). On Earth, dry ice doesn't occur naturally; our atmosphere is too thick and warm for CO₂ to freeze. We manufacture it in small amounts for shipping frozen foods and creating fog effects on stage. Rather than CO₂ gas jets, our planet features liquid water geysers. The same fundamental physical laws apply on Earth, yielding different results under different conditions. Martian dry geysers are as unique in the solar system as our liquid ones.. In its unbounded creativity, nature avoids repetition, making each planet one os a kind.

Martian gravity

Mars' surface gravity is 0.38 g, meaning you’d weigh there 38% of your Earth weight. A person weighing 100 kilograms on Earth would weigh 38 kilograms on Mars, feeling as if they instantaneously lost 62 kilograms. This would make tasks like wearing spacesuits and lifting heavy equipment much easier. However, what appears to be an advantage comes with uncertainties. Our experience with low gravity's effects on the human body is limited, with data only from astronauts' brief stays in microgravity on the International Space Station. Despite rigorous exercise, astronauts face muscle loss, bone thinning, and vision changes. We lack long-term data on how the human body responds to partial gravity. We don’t yet know how well humans can grow, age, or even have children under such conditions.

Why Mars?

If Mars is so inhospitable and challenging, then why have we chosen this planet for future colonization? The answer starts with simple planetary bookkeeping. Of the eight planets in our Solar System, four are gas giants: Jupiter, Saturn, Uranus, and Neptune. They have no solid surfaces, only deep, violent atmospheres of hydrogen and helium. There is nowhere to land, stand, build, or breathe. That leaves us with two remaining rocky planets.

Mercury is a tiny planet of extremes, where survival is unfeasible. Due to its almost nonexistent atmosphere, which fails to retain or distribute heat, temperatures swing violently from +430 °C (+800 °F) during the day to –180 °C (–290 °F) at night. A single day on Mercury spans nearly two Earth months, giving the surface plenty of time to bake and then freeze. It’s a place where metal softens in the daytime and gases turn into frost at night.

In contrast, Venus is a high-pressure furnace. Its surface temperature averages 465 °C (869 °F), hot enough to melt lead, and the atmospheric pressure is 92 times that of Earth, sufficient to destroy your internal organs. Dense clouds of sulfuric acid trap heat, causing a runaway greenhouse effect that renders Venus not only extremely hot but also overwhelmingly hostile. Even the most durable probes can survive just for a few minutes before being fried, flattened, and corroded.

Through a process of elimination, Mars stands out as the only planet in our neighbourhood where humans could potentially survive. While it may not be an ideal host, it does offer water ice, a day length similar to Earth's at nearly 24 hours, and an atmosphere, though thin, still suitable for future greenhouse warming. Admittedly, it falls short of providing our usual home comforts. But if we ever aim to establish a long-term presence on another planet, Mars remains our only viable option for survival, at least among the choices within the Solar System.