The definitive answer to whether air on Mars is breathable is no. The planet’s atmosphere presents an extreme environmental challenge that is instantly lethal to unprotected human life, characterized by extremely low pressure, frigid temperatures, and a toxic chemical composition. Any human venturing onto the Martian surface must rely entirely on a self-contained, pressurized suit to survive. The conditions on Mars are more akin to a vacuum than a conventional atmosphere.
The Composition of the Martian Atmosphere
The Martian atmosphere is vastly different from Earth’s, averaging only about 6 to 7 millibars at the surface, which is less than one percent of Earth’s sea-level pressure. This ultra-thin gas layer is incapable of supporting human respiration or maintaining liquid water on the surface. For comparison, a person on Earth would need to be at an altitude of approximately 28 miles (45 kilometers) to experience such low pressure.
Chemically, the air is overwhelmingly composed of carbon dioxide (\(\text{CO}_2\)), making up about 95 percent of the total volume. The remaining gases consist primarily of molecular nitrogen (2.8 percent) and argon (2 percent). Molecular oxygen (\(\text{O}_2\)), which is necessary for human life, is virtually non-existent, registering only about 0.13 to 0.17 percent.
Physiological Effects of Martian Conditions
The lack of atmospheric mass and the toxic gas composition create two primary, immediate physiological threats to an unprotected person. The first threat is rapid asphyxiation, caused by the lack of oxygen and the high concentration of carbon dioxide. Inhaling air that is 95 percent \(\text{CO}_2\) would cause immediate carbon dioxide poisoning.
The second threat is ebullism, the boiling of bodily fluids. Because the atmospheric pressure is so low, it falls below the vapor pressure of water at human body temperature (98.6°F/37°C). Within seconds of exposure, water in the soft tissues and blood would begin to vaporize, causing severe swelling and tissue damage, leading to unconsciousness in less than 20 seconds.
Beyond these immediate dangers, the planet’s average temperature hovers around -81°F (-63°C), adding a severe thermal hazard. The thin atmosphere provides very little shielding from solar and cosmic radiation. Surface radiation levels are significantly higher than on Earth, posing a long-term health risk even inside a habitat.
Current Methods for Oxygen Production
Current technological efforts focus on generating breathable oxygen from the existing Martian atmosphere through In-Situ Resource Utilization (ISRU). The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE), aboard the Perseverance rover, is the first demonstration of this technology. MOXIE pulls in the carbon dioxide-rich Martian air and uses solid oxide electrolysis to separate one oxygen atom from each \(\text{CO}_2\) molecule.
This electrochemical process requires heating the atmospheric gas to approximately 800°C (1,472°F) to efficiently split the molecules. The instrument successfully demonstrated that oxygen can be reliably produced in the Martian environment at a purity of 98 percent or better, suitable for both breathing and rocket propellant. A scaled-up version of this technology could produce the large quantities of oxygen needed for life support and for the rocket fuel required to launch a crewed mission back to Earth.
MOXIE proves that future astronauts can “live off the land” by generating resources rather than transporting them from Earth. This success validates the concept of using the planet’s native resources for sustainable human exploration. The next generation of oxygen generators will need to be larger and include systems for liquefying and storing the produced gas.
Planetary Scale Atmospheric Modification
The concept of creating a permanently breathable atmosphere across the entire planet is known as terraforming. This planetary engineering would require significantly increasing the atmospheric mass to raise the surface pressure and temperature. One theoretical approach involves releasing the vast stores of frozen carbon dioxide locked within the polar ice caps and the surface regolith.
This release could be triggered by introducing powerful greenhouse gasses or using orbital mirrors to warm the poles, initiating a runaway greenhouse effect. However, research indicates that even if all known \(\text{CO}_2\) reserves were vaporized, the resulting atmosphere would still be too thin to sustain liquid water or human respiration. A more challenging issue is Mars’ lack of a global magnetic field, which allows solar winds to continuously strip away any newly generated atmosphere.
Achieving a long-term, self-sustaining breathable atmosphere would require restoring a planetary magnetic shield, a feat far beyond current technological capabilities. While local oxygen production is a near-term reality, the planetary-scale modification required to make the entire Martian sky breathable remains a highly theoretical, distant prospect.