The long-held dream of transforming Mars into a second Earth, a so-called “terraforming” process, faces insurmountable obstacles with present-day technology, according to a consensus of scientific analysis. Decades of data from orbiters and landers paint a stark picture of a world that cannot be easily engineered for human habitation. The fundamental challenges are now understood to be far more immense than early theories suggested, involving a cascade of interconnected problems from a vanishingly thin atmosphere to a toxic, irradiated surface.
Transforming the Red Planet would require warming the climate, thickening the air, and establishing a stable water cycle. Yet, detailed planetary inventories reveal Mars has lost the key ingredients needed for such a makeover. The planet lacks the accessible carbon dioxide reserves required to create a greenhouse effect, its soil is saturated with chemicals poisonous to Earth-life, and the entire world is bathed in a constant flux of life-altering radiation. These core realities have shifted the scientific conversation from planetary engineering to the more practical, albeit still difficult, challenge of building shielded, localized habitats.
A Ghost of an Atmosphere
The most immediate barrier to a habitable Mars is its atmosphere. With a surface pressure averaging just 0.6% of Earth’s, liquid water cannot persist; it either freezes solid or boils away into the thin air. Proponents of terraforming have long theorized that Mars holds vast reserves of frozen carbon dioxide (CO2) in its polar caps and soil that could be vaporized to thicken the atmosphere, trapping heat through a powerful greenhouse effect.
However, a landmark NASA-sponsored study dashed these hopes by creating a comprehensive inventory of Mars’ accessible CO2. The research, led by Bruce Jakosky of the University of Colorado, Boulder, concluded that even if humans could sublimate the entire volume of the polar ice caps, the atmospheric pressure would only increase to about 1.2% of Earth’s. Tapping every other known source—including CO2 bonded to dust particles in the soil and buried in mineral deposits—would, at best, raise the pressure to around 7% of what is needed to make Mars habitable. The stark conclusion is that the vast majority of Mars’s ancient, thicker atmosphere was stripped away into space over billions of years, a process that continues today.
An Unshielded and Irradiated World
The reason for Mars’s atmospheric loss is the absence of a global magnetic field. Unlike Earth, whose molten core generates a protective magnetosphere that deflects high-energy solar particles, Mars’s core cooled long ago, leaving it defenseless. For eons, the solar wind has scoured the Martian atmosphere, carrying its gases out into the cosmos.
This lack of protection has two critical consequences. First, any new atmosphere would also be stripped away, making any terraforming effort a temporary and constantly failing battle against physics. Second, the surface is exposed to dangerous levels of solar and galactic cosmic radiation. Measurements from the Curiosity rover show that an astronaut on Mars would be exposed to an average of 240 to 300 millisieverts per year, a dose 40 to 50 times higher than the natural background radiation on Earth. This constant bombardment is sufficient to damage unprotected DNA and poses a lethal long-term threat to humans and most forms of terrestrial life, making surface operations without significant shielding impossible.
The Poisoned Ground
Even if the atmospheric and radiation challenges could be solved, the Martian ground itself presents another profound obstacle. Data from the Phoenix lander and subsequent missions confirmed that the Martian regolith, or soil, is saturated with a class of chemicals called perchlorates. These salt compounds, found in concentrations up to 1% in some samples, are toxic to the human thyroid gland and harmful to many microorganisms and plants.
Remediation on a Planetary Scale
Experiments using simulated Martian soil have shown that the high concentration of perchlorates can prevent the germination of seeds altogether. While methods to clean contaminated soil exist on Earth—such as washing the soil or using specialized microbes that consume the chemicals—the scale of the problem on Mars is staggering. Implementing such solutions would require immense quantities of water, which is not readily available in liquid form, and vast amounts of energy and equipment. Furthermore, the perchlorates make the fine Martian dust a significant health hazard that would require rigorous decontamination procedures for any habitat or spacesuit that comes into contact with it.
Impractical Planetary Engineering
The physical realities of Mars have forced a re-evaluation of popular terraforming concepts. The idea of using explosives or spreading dark dust on the polar caps to release CO2 is now understood to be insufficient, as there simply isn’t enough frozen gas to make a meaningful difference. Other proposals, such as importing volatile-rich comets or asteroids to deliver water and atmospheric gases, face equally daunting energy and logistical challenges. The sheer mass of material needed would require quadrillions of tons to be moved across the solar system, an undertaking far beyond any conceivable technology.
Without an active planetary core to drive geologic activity like plate tectonics, Mars also lacks a mechanism for a stable, long-term carbon cycle. On Earth, volcanism and other geologic processes naturally replenish atmospheric gases, but Mars is largely a geologically quiet world. Any attempt to artificially create a biosphere would be fighting a losing battle against these fundamental planetary limitations.
From Terraforming to Habitation
In light of these immense challenges, the scientific and engineering focus for human exploration is shifting away from planetary-scale terraforming. Instead, the consensus is moving toward the establishment of permanent, self-contained, and heavily shielded habitats. These enclosures, likely built underground or covered with thick layers of regolith for radiation protection, would allow humans to live and work on Mars in a controlled and safe environment.
Within these closed systems, colonists could create localized ecosystems, grow food using hydroponics or in carefully processed Martian soil, and recycle vital resources like air and water. This approach acknowledges the harsh realities of the Martian environment while still allowing for a long-term human presence. While the dream of a green, Earth-like Mars may remain in the realm of science fiction for the foreseeable future, the more pragmatic goal of becoming a multi-planetary species by living *on* Mars, rather than remaking it, continues to drive exploration forward.
