Is Mars Habitable? The Science of Life on the Red Planet

The question of whether Mars is habitable is a complex issue. The definition of “habitable” is twofold: it can refer to the possibility of microscopic life existing, or the potential for humans to establish self-sustaining colonies. For astrobiologists, habitability requires liquid water, an energy source, and chemical building blocks for life. For human exploration, it involves creating an artificial environment with breathable air, water, food, and protection from Martian conditions.

Mars’s Current Inhospitable Conditions

Mars today is a hostile environment. Its atmosphere is exceedingly thin, with a surface pressure less than 1% of Earth’s. This thin air, composed of 95% carbon dioxide, cannot retain significant heat, leading to dramatic temperature swings from -153° C to 20° C.

The planet also lacks a global magnetic field to shield it from dangerous space radiation. Without this protection, the Martian surface is bombarded by cosmic rays and solar particles. The average daily radiation dose is around 0.64 millisieverts, a level that is sterilizing to life as we know it.

Any liquid water on the surface would instantly boil or freeze due to the low atmospheric pressure. The little water that remains exists as ice at the polar caps or sublimates directly into gas. This combination of a thin atmosphere, extreme cold, and high radiation makes the surface of Mars inhospitable.

Clues to a Watery Martian Past

Despite its current state, evidence suggests Mars was not always a frozen desert. Billions of years ago, the planet was likely warmer with a thicker atmosphere that supported liquid water on its surface. This raises the possibility that Mars could have once been habitable for microbial life.

The geology of Mars reveals this history, with spacecraft imaging vast, dried-up riverbeds and deltas. NASA’s Perseverance rover is exploring the Jezero Crater, which data confirms was once a lake fed by a river. The rover’s ground-penetrating radar has revealed layers of sediment deposited by water, similar to lakebeds found on Earth.

Within these ancient lakebeds, rovers have discovered minerals that form in the presence of water, including clays, carbonates, and sulfates. The detection of silica and quartz also suggests a history of hydrothermal activity, which on Earth is known to support microbial life.

Sourcing Life-Sustaining Necessities

For humans to live on Mars, they must source necessities locally. Water is too heavy to transport from Earth, but Mars has vast reserves of water ice in its polar caps and buried underground. Future missions could use drilling technologies to melt this subsurface ice and pump liquid water to the surface.

Oxygen is virtually absent, but it can be created from the atmosphere’s abundant carbon dioxide. NASA’s Perseverance rover carried an instrument called the Mars Oxygen In-situ Resource Utilization Experiment, or MOXIE. This device successfully demonstrated that oxygen can be electrochemically separated from carbon dioxide molecules, producing 122 grams of oxygen and proving the technology’s viability.

Producing food is also a challenge because Martian soil is toxic and lacks organic matter. Settlers would need enclosed greenhouses using soil-free farming methods like hydroponics or aeroponics to cultivate crops in a protected environment.

Mitigating Planetary Dangers

A human presence on Mars requires defense against the planet’s dangers, primarily the high level of solar and cosmic radiation. Habitats, vehicles, and spacesuits must incorporate advanced radiation shielding. One practical solution involves using Martian soil, or regolith, as a building material, as a one-meter-thick layer provides substantial protection. Other materials being studied include water, polyethylene, and advanced synthetic fibers.

The fine Martian dust is another hazard, as the soil contains toxic perchlorates. These compounds are harmful if inhaled or ingested and can interfere with thyroid function. Strict protocols would be needed to prevent dust contamination, such as specialized suitports that allow astronauts to enter a habitat without bringing their dusty spacesuits inside.

The Prospect of a Habitable Future

Scientists have considered terraforming Mars to make it more Earth-like. The idea involves thickening the planet’s atmosphere to create a greenhouse effect, warming the surface enough for liquid water. This would be accomplished by releasing the carbon dioxide frozen in the polar ice caps and trapped in the soil.

Proposed methods for releasing this trapped CO2 range from spreading dark dust on the poles to absorb more solar radiation to more extreme ideas like using explosives. If the atmosphere could be thickened sufficiently, it would initiate a feedback loop where a warmer climate releases more gas, further increasing the temperature and pressure.

This vision, however, remains in the realm of science fiction for now. A NASA-sponsored study concluded that Mars lacks enough accessible carbon dioxide to create a significant greenhouse effect with current technology. Transforming an entire planet would require centuries and technologies far beyond our present capabilities.