The concept of terraforming Mars was first proposed by John B. S. Haldane in his 1927 essay “On Being the Right Size”, where he touches on the idea of altering planetary environments to make them habitable for humans, including Mars. However, the term “terraforming” itself was coined later by science fiction author Jack Williamson in his 1942 story “Collision Orbit”, where he described transforming alien worlds into Earth-like environments. Haldane’s speculative mention in 1927 is generally considered the earliest recorded proposal of the concept applied to Mars, though it was not detailed or Mars-specific. More technical discussions of Mars terraforming emerged in the mid-20th century with advancements in space science.

Carl Sagan discussed terraforming Mars in his scientific work and popular writings. In a 1971 paper, “The Long Winter Model of Martian Biology: A Speculation”, published in Icarus, Sagan explored the idea of making Mars habitable by using dark-colored plants or microorganisms to reduce the planet’s albedo, leading to better absorption of sunlight to warm the surface, which would release water and carbon dioxide from the polar caps and regolith. This would thicken the atmosphere and create conditions suitable for life. His ideas influenced later science fiction, including Kim Stanley Robinson’s magnus opus Mars trilogy, and remain a foundation for modern terraforming discussions.

The research up until now indicate that it is a complex, long-term project, taking hundreds of years and could be controversial due to ethical challenges. In an article in Nature Astronomy, a fresh look using innovative terraforming methods is presented which could accelerate the warming of Mars by at least 30°C within a few decades, although complete habitability for human flourishing would likely take at least a century. The paper emphasizes the need for scientific research to understand if and how this could be done. Ethical concerns are also addressed with care in the paper.

The article suggests that terraforming Mars should progress in three phases: first, warming the planet; then, introducing hardy organisms to start an ecosystem; and finally, engineering a biosphere with enough oxygen to support human life. The technology proposed to facilitate warming of the planet in the first phase includes orbiting solar sails, silica aerogels, nanocellulose, and engineered aerosols.

Large, lightweight reflective solar sails deployed in space would act as mirrors to reflect solar radiation on to the Martian surface, increasing the amount of heat the planet absorbs. The paper notes that the current insolation of Mars is ~130 W/m², with net absorbed energy at ~125 W/m², resulting in an average surface temperature of about -63°C. By redirecting additional sunlight, reflectors in orbit could significantly boost this energy input which would raise the surface temperature.

Ultra-light, porous silica aerogels with excellent insulating properties could be deployed in transparent or translucent blankets over Martian ice deposits, particularly in polar or high-latitude regions with abundant frozen water reserves. Aerogels trap heat by allowing sunlight to penetrate while preventing infrared radiation from escaping, creating a localized greenhouse effect. This would warm the underlying ice, potentially melting it without requiring global atmospheric changes. The paper emphasizes the aerogel’s biocompatibility, ensuring they would not harm the existence of a potential Martian ecosystem.

Nanocellulose is a lightweight, strong, and renewable nanomaterial derived from cellulose, It could be spread over the Martian surface acting as a thermal blanket similar to aerogels, or as a component in structures that trap heat. The paper suggests it could be tailored to maximize solar absorption in the visible spectrum while reflecting infrared to retain heat, contributing to localized or regional warming. Nanocellulose could support targeted warming, potentially complementing aerogels in creating habitable microenvironments. Its lightweight nature makes it practical for transport and deployment, aligning with the paper’s focus on mass-effective solutions.

Engineered aerosols are fine particles designed to be released into Mars’ thin atmosphere to enhance its greenhouse effect. Unlike older fluorocarbon proposals, which were less efficient and environmentally risky, these aerosols are optimized for biocompatibility and ease of control. These aerosols absorb and scatter solar radiation, trapping heat in the atmosphere. They can be tailored to target specific wavelengths, maximizing heat retention while minimizing harmful effects on potential biology. The paper notes that Mars’ low heat capacity allows these aerosols to warm the planet faster than on Earth, potentially achieving a 30°C increase within a century. By thickening the atmosphere’s greenhouse layer, aerosols could raise global or regional temperatures, facilitating the melting of ice and the release of water vapor, which further enhances warming because water vapor itself is a greenhouse gas.

Another option to facilitate atmospheric warming, proposed in a paper in Scientific Advances last year, would be to engineer and mass produce “nanorods” from Martian regolith tuned to strongly absorb infrared radiation, thereby supercharging a greenhouse effect.

Mid-term, anaerobic organisms tolerant to Mars’ harsh conditions could be introduced, initiating ecological succession and producing oxygen. The lead author on the Nature Astronomy paper is Erika Alden DeBenedictis, CEO of the San Francisco based nonprofit Pioneer Labs, who’s mission is to engineer microbes that can thrive in extreme environments. As stated on the website, “These new pioneer species can pave the way to greener planets by remediating soil, upcycling waste streams, and making harsh areas more friendly to life.”

SSP has covered a similar approach to terraforming the Red Planet with introduction of pioneer species such as the desert moss Syntrichia caninervis, an organism that can survive the frigid temperatures, low ambient pressure and harsh radiation on Mars while helping to boost oxygen levels and fostering soil fertility.

This middle phase would be ideal for para-terraforming, a more limited approach to making localized regions of Mars habitable, prior to fully terraforming the entire planet. It involves creating enclosed, controlled environments—such as domed habitats or sealed craters—where temperature, atmosphere, and other conditions are artificially maintained to support human life or simple ecosystems. Kent Nebergall, chairman of the Mars Society Steering Committee, has proposed this approach by building an enclosure over Hebes Chasma, a canyon the size of Lake Erie just north of Valles Marineris.

The Space Development Network has also advocated for this approach.

The paper suggests terraforming in this middle phase could support upwards of 10,000 people per site with automated farming, while the end goals are constrained by physical, chemical, and biological limits, perhaps necessitating a multicentury timeline. This phased approach highlights the gradual, research-driven nature of the project, acknowledging the long timescales involved.

The final phase involves establishing a sustainable, oxygen-rich ecosystem capable of supporting advanced plant life and, eventually, the ability to support human settlements without life support systems. Atmospheric oxygen would be increased to at least 0.1 bar to enable humans to breathe without pressure suits. This would be achieved through the widespread propagation of photosynthetic organisms like engineered plants or cyanobacteria. The paper notes that this slow oxygen build-up, potentially taking over a century, requires sustained energy inputs, possibly from multi-terawatt power sources or solar concentrators, to accelerate the process. The project would need ongoing climate engineering to maintain temperature and pressure, such as controlled greenhouse gas releases. Because Mars does not have a magnetic field to deflect solar particle events and galactic cosmic rays, engineered solutions would be required to prevent loss of oxygen and to shield Martian settlers from radiation. Through deployment of large-scale electromagnetic coils or magnetic shields in orbit or on the surface, a localized or planetary magnetic field could be created, mimicking Earth’s magnetosphere. This concept has been proposed by Dr. James Green, former chief scientist at NASA who retired from that role in 2022.

With respect to ethical concerns, there is considerable debate over preserving Mars as a pristine environment versus transforming it, with implications for potential Martian life that may exist there. The paper notes that human presence during exploration and/or settlement will introduce orders of magnitude more Earth microbes (then those that may have been present on probes that have already landed there), necessitating a search for extant Martian life through sample returns and deep aquifer exploration prior to initiation of terraforming efforts. The authors suggest that terraforming technologies could benefit Earth, such as developing desiccation-resistant crops, but emphasize the need for science-informed engagement with stakeholders. The long timescale for terraforming is noted as a constraint for politics and science, highlighting the need for long-term planning and international cooperation.

There are more audacious proposals such as Robert Zubrin and Chris McKay’s plan for terraforming Mars in 50 years. Zubrin, a prominent advocate for Mars exploration and terraforming, argues that there is no extant life on Mars, thus alleviating ethical concerns about altering the planet’s environment soon. In his view put forward in his book The Case for Mars, extensive scientific investigations analyzing data from Mars rovers and orbiters, have found no conclusive evidence of current microbial or other life forms, suggesting Mars is a barren world. He contends that the absence of indigenous life eliminates moral objections to terraforming, as there are no ecosystems to disrupt or native species to harm. Zubrin emphasizes that terraforming Mars into a habitable environment for humans, would foster scientific advancement and human expansion without ethical conflicts, provided ongoing searches for life—such as soil sample returns—continue to yield negative results. This position is echoed in the paper which notes the need to confirm the absence of life through further exploration but supports initiating terraforming research given the evidence to date.

As Mars terraforming efforts advance, the viability of the planet as a sustainable environment for surface settlements may progress according to the Pancosmorio Theory which posits that ecosystems necessary to sustain life gradually acquire sufficient area and availability of resources (e.g. sources of energy) as their circular economies evolve toward closure such that dependency on supply chains from Earth begins to diminish.

The paper makes a compelling case for prioritizing Mars terraforming research, aligning with current exploration priorities while informing future decisions about an eventual human presence on Mars. The authors acknowledge the complexity, controversy, and long-term nature of the project, advocating for a science-driven approach to address feasibility, ethics, and potential benefits for both Mars and Earth.

Dr. DeBenedictis will be discussing these topics in a plenary talk titled “Opportunities for a Green Human Civilization on Mars” at the Mars Society Convention next month.

Cutting-edge technology enabling settlement of the solar system and beyond – Art by Rick Guidice / NASA