Mars, our celestial neighbor, has long fascinated humanity with its reddish hue. This distant world harbors an atmosphere profoundly different from Earth’s. Its unique conditions have shaped its landscape and influence its environment, presenting scientific puzzles and opportunities for exploration.
Current Composition and Characteristics
The Martian atmosphere is remarkably thin compared to Earth’s, with an average surface pressure of about 6 to 7 millibars. It is predominantly carbon dioxide, comprising approximately 95.3% of its volume. Other gases include nitrogen (2.7%), argon (1.6%), oxygen (0.13%), carbon monoxide, and water vapor.
The low atmospheric density on Mars results in temperature fluctuations. While equatorial regions can reach 20 degrees Celsius (70 degrees Fahrenheit) at midday, temperatures can plummet to around minus 125 degrees Celsius (minus 195 degrees Fahrenheit) near the poles during winter. This wide range is also due to Mars’ greater distance from the Sun, receiving only about 43% of Earth’s sunlight. The thin atmosphere and low pressure mean that water can only exist as ice or vapor, not as liquid.
Atmospheric Phenomena
Despite its thinness, the Martian atmosphere exhibits weather. The most prominent are global dust storms, obscuring much of the planet for months. These storms are common during the southern spring and summer when Mars is closest to the Sun. Smaller, more localized dust storms and dust devils are also observed across Mars.
Clouds form, consisting of water ice and carbon dioxide ice particles. Water ice clouds gather near the planet’s large volcanoes, where updrafts cool the thin air, causing ice to condense. Broad hazes known as polar hoods, composed of water and carbon dioxide ice, form over the polar regions during local autumn and winter. These seasonal changes are linked to the freezing and sublimation of a portion of the atmosphere’s carbon dioxide onto the polar caps, leading to a seasonal drop in global atmospheric pressure by 25% to 30%.
Evolution and Loss of the Martian Atmosphere
Mars’ atmosphere has undergone a significant transformation over billions of years, shifting from a thicker and warmer state to its current thin and cold condition. Scientists believe that early Mars had a denser atmosphere, possibly supporting liquid water on its surface. The primary mechanism for this atmospheric loss is solar wind stripping, where charged particles from the Sun interact with the planet’s upper atmosphere and accelerate gases into space.
Unlike Earth, Mars lacks a global magnetic field, which would otherwise deflect the solar wind. Mars is a smaller planet than Earth, causing it to lose its internal heat more rapidly. This faster cooling caused its molten iron core to solidify, shutting down the planet’s magnetic field approximately 3.7 billion years ago. Without this magnetic shield, the solar wind has been eroding the Martian atmosphere over geological timescales. Measurements from missions like NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) indicate that the solar wind currently strips away about 100 grams of gas per second, with this rate increasing during solar storms.
Implications for Life and Exploration
The current atmospheric conditions on Mars present challenges for present-day surface life and human exploration. The thin atmosphere, composed primarily of carbon dioxide, is unbreathable for humans, necessitating pressurized habitats and life support systems for long-term missions. Additionally, the absence of a global magnetic field leaves the surface exposed to high levels of cosmic radiation, which is harmful to organic compounds and biological systems.
Despite these challenges, the Martian atmosphere also offers opportunities for in-situ resource utilization (ISRU), a concept where resources on Mars are used to support missions. The abundant carbon dioxide in the atmosphere can be converted into oxygen, necessary for breathing and as a component of rocket propellant. The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) on NASA’s Perseverance rover has demonstrated the feasibility of producing oxygen from the Martian atmosphere. This ability to generate resources locally could reduce the amount of supplies that need to be transported from Earth, making long-duration human missions more viable.