Mars is a freezing world where carbon dioxide falls as dry ice snow. Yet for an astronaut walking outside, the biggest temperature threat isn't freezing to death—it's heatstroke.
The planet orbits about 50 million miles further from the sun than Earth, receiving significantly less solar energy. Compounding this distance is an atmosphere roughly 100 times thinner than Earth’s. This thin gaseous envelope cannot trap heat via a strong greenhouse effect. While a summer day near the Martian equator can reach a comfortable 70°F (20°C) at noon, the lack of atmospheric insulation means that as soon as the sun sets, temperatures plummet. Nighttime at the poles can drop to -220°F (-140°C).
However, that same thin atmosphere changes how cold actually behaves. On Earth, dense air or water rapidly pulls heat away from the body through conduction and convection. Because the Martian atmosphere is nearly a vacuum, it lacks the molecular density to efficiently steal heat. If a person stood outside on Mars, they would lose body heat much slower than they would on a severe winter day in Antarctica.
Because of this, the human body—acting as a 100-watt furnace at rest—quickly becomes a liability. A pressurized spacesuit is essentially a specialized thermos. With so few atmospheric molecules outside to carry heat away, internal life-support systems have to actively pump excess heat out of the suit to keep the wearer safe during physical exertion.
Designing structures to survive the cold is a highly understood science. Researchers have lived for decades in Antarctica’s Amundsen-Scott South Pole Station, managing temperatures that regularly drop to -100°F. Martian habitats will use heavy insulation and active heating systems, relying on the near-vacuum outside to act as a highly effective insulating layer.
While Mars is far too cold to live on unprotected, engineering can easily mitigate the extreme temperatures. The real barriers to long-term settlement are not the chilling nights, but unshielded cosmic radiation, toxic perchlorate compounds in the soil, and the total lack of breathable oxygen.