The Challenge of Terraforming Mars
Mars, often called Earth’s sister planet, was once a very different world. Billions of years ago, Mars likely had a thicker atmosphere, higher surface temperatures, and liquid water flowing on its surface – conditions that may have supported the emergence of life. But the Red Planet lost its magnetic field around 4 billion years ago, allowing the solar wind to strip away most of its atmosphere over hundreds of millions of years. This transformed Mars into the cold, dry planet we see today, with atmospheric pressure less than 1% that of Earth’s and average temperatures around -80°F (-60°C).
The idea of terraforming Mars – engineering its environment to make it habitable for Earth life, including humans – has long captured the imagination of scientists and science fiction authors alike. Terraforming Mars would be a colossal undertaking, requiring a series of complex and interconnected processes to thicken the atmosphere, raise temperatures, and create stable bodies of liquid water on the surface. It would likely take many centuries, if not millennia, to fully terraform the planet. However, even partial terraforming to make regions of Mars habitable for plants and eventually humans may be achievable with future technology.
Thickening the Martian Atmosphere
The first major step in terraforming Mars would be to massively increase the density and pressure of its atmosphere, which is currently far too thin to support liquid water or Earth life. Mars’ atmosphere is over 95% carbon dioxide (CO2), so thickening it would have a strong greenhouse effect, trapping more heat and raising surface temperatures.
One proposed method is to release the CO2 frozen in the Martian polar ice caps by heating them, possibly using giant orbital mirrors to reflect more sunlight onto the poles. The ice caps contain enough CO2 to roughly double Mars’ atmospheric pressure if fully sublimated. However, this would still leave the atmosphere far thinner than Earth’s.
Additional CO2 could potentially be extracted from Martian soil and minerals, which contain much larger reserves than the polar caps. Industrial-scale processing and heating of the regolith could release this CO2, but would require enormous amounts of energy. Alternatively, super-greenhouse gases like perfluorocarbons, which are extremely potent at trapping heat, could be manufactured on Mars to more efficiently warm the planet.
Another option is to import volatile materials like ammonia from the outer solar system, by redirecting comets and ice-rich asteroids to impact Mars. However, this would require tremendous advances in space infrastructure and propulsion technology to be feasible.
Even if the atmosphere could be thickened by several times, it would still be gradually lost to space due to Mars’ lack of a strong magnetic field. Protecting Mars from the solar wind, perhaps using a giant magnetic shield in orbit, may be necessary for long-term atmospheric stability.
Raising Temperatures and Melting Ice
As the Martian atmosphere thickens and traps more heat, global temperatures would rise, expanding the regions where liquid water could exist on or near the surface. Once atmospheric pressure exceeds about 0.006 atm (the triple point of water), pure water ice will melt into liquid when heated rather than sublimating directly into gas.
Temperatures could be raised further by darkening areas of Mars’ surface, reducing its albedo (reflectivity) so that it absorbs more solar energy. This could be done by spreading dark dust, placing heat-absorbent materials over large areas, or growing dark-colored plants or lichen. However, significant temperature increases would only occur once the atmosphere has been substantially thickened.
Higher temperatures would cause much of Mars’ water ice to melt, creating new lakes or seas. The Martian poles hold the equivalent of a global layer of water 20-30 meters deep, and even more water is thought to be frozen underground. Liquid water would enable the growth of plants and microbes that could further enrich and oxygenate the atmosphere.
Creating a Breathable Atmosphere
For humans to eventually walk on the surface of Mars without pressure suits, the atmosphere would need to be thickened to at least 0.2-0.3 atm (about the pressure at the top of Mount Everest) and contain sufficient oxygen. Earth’s atmosphere is about 20% oxygen, maintained by photosynthetic plants and algae.
On a terraformed Mars, oxygen could be produced biologically by plants or algae, or artificially by splitting water molecules. Either process would require a large, continuous energy input. Genetically engineered plants and microbes may be able to survive and spread in the harsh Martian environment, jump-starting the oxygenation process.
Nitrogen, the bulk of Earth’s atmosphere, would also need to be sourced and added to the air. Nitrogen in the form of nitrates has been detected in Martian soil and could potentially be extracted, but the quantities are unknown.
Even with a thicker, more breathable atmosphere, Mars’ greater distance from the Sun means that surface temperatures and atmospheric pressure would always be significantly lower than Earth’s. Atmospheric pressure might reach 0.3-0.5 atm at best, compared to 1 atm on Earth, and equatorial daytime highs may only reach 10-20°C (50-68°F) even after centuries of terraforming. But these conditions, comparable to high mountain environments on Earth, would still be far more hospitable to life than the current Martian surface.
Challenges and Uncertainties
The immense scale, technological hurdles, and uncertain outcomes make terraforming Mars a highly speculative endeavor. Thickening the atmosphere would require processing unimaginable quantities of raw materials – the polar CO2 deposits alone are estimated at nearly 1 million cubic kilometers. Raising temperatures and pressures to the minimal levels for liquid water and terrestrial life could take 100-1000 years, and achieving a fully breathable atmosphere would likely take several thousand years at minimum.
Our current understanding of Mars’ total inventory of carbon, nitrogen, and water is still incomplete, making it unclear if the planet holds sufficient accessible quantities to terraform with. Surveys by future robotic explorers and human missions will be needed to better constrain these numbers.
The responses of the Martian environment to terraforming efforts are also difficult to predict. Feedback loops, such as the release of additional greenhouse gases from the heating regolith, could accelerate warming, but may prove difficult to control. Dust storms, which can already engulf the entire planet, may become more frequent and intense as the atmosphere thickens, with unknown consequences.
Perhaps the greatest uncertainty is whether a terraformed Mars could maintain stable, habitable conditions in the long-term without continuous human intervention. Mars lacks plate tectonics and a strong magnetic field, two key stabilizing factors for Earth’s atmosphere and climate. Atmospheric loss to space would continue at a much higher rate than on Earth, potentially undoing terraforming efforts on timescales of millions of years unless technological solutions can be implemented.
Alternatives to Terraforming
Given the immense challenges of terraforming Mars, other options for enabling a long-term human presence should also be considered. Habitats could be constructed with enclosed, pressurized atmospheres and hydroponic agriculture to support small human populations with minimal alteration of the Martian environment. These could be built underground or in natural caverns to protect from radiation and extreme temperature swings.
Paraterraforming, or the creation of habitable artificial environments within domes or caverns on Mars, offers a more achievable path than transforming the entire planet. Cities could be constructed with breathable air, comfortable temperatures, and Earth-like levels of atmospheric pressure. While still an enormous undertaking, paraterraforming could be accomplished with more readily available materials and technology.
Orbiting space habitats are another alternative, providing complete control over environmental conditions. Large spinning habitats could create artificial gravity and be supplied with abundant solar energy. While more dependent on advanced technology than surface habitats, orbital cities have the advantage of mobility and could be more easily expanded over time.
Conclusion
Terraforming Mars is an incredible long-term vision for expanding humanity’s presence in the solar system. With sufficient time and technological advancement, transforming the Red Planet into a second Earth may be an achievable goal. However, the immense scale, uncertain feasibility, and multi-millennial timescans required mean that terraforming remains a highly speculative prospect.
In the nearer term, more modest goals of establishing permanent human habitats on or around Mars are likely to take precedence. Robotic exploration to better understand the Martian environment and identify exploitable resources will lay the groundwork. This could be followed by the construction of small research outposts and eventually self-sustaining colonies, perhaps under domes or in subsurface caverns. These settlements could gradually expand and incorporate more ambitious terraforming efforts as technology progresses.
Ultimately, the question of whether to terraform Mars is as much philosophical as technical. Even if we gain the ability to reshape entire planets, we must consider the ethical implications of fundamentally and permanently altering another world. These decisions will not be made lightly, and will require input from all of humanity. But the knowledge and technologies gained in the attempt – from living in closed-loop habitats to modifying planetary climates – may prove vital to our species’ long-term survival, whether on Earth or amongst the stars.
