Which characteristic is NOT true about the Martian atmosphere?

The Martian atmosphere is primarily composed of carbon dioxide, making the statement that it is primarily composed of oxygen false. In fact, the atmosphere consists of about 95% carbon dioxide, with only trace amounts of oxygen (less than 0.2%). This composition is crucial because it fundamentally affects the conditions on Mars, including its ability to support life as we know it and the presence of liquid water.

The low pressure of the Martian atmosphere is indeed true, as it is less than 1% of Earth's atmospheric pressure at sea level. This low pressure contributes to the difficulty in sustaining liquid water on the surface, as water would typically evaporate quickly under such conditions.

Additionally, the atmosphere's inability to support liquid water long-term is accurate. Due to the low pressure and cold temperatures, any liquid water that may be present would either freeze or evaporate rapidly.

Finally, the lack of sufficient density in the Martian atmosphere also holds true. The thin atmosphere does not provide enough protection from solar and cosmic radiation, and it cannot retain heat effectively, making the Martian surface very cold.

Thus, the characteristic that is not true about the Martian atmosphere is that it is primarily composed of oxygen.