Martian Windchill in Terrestrial Terms

Abstract

verage temperature of ?63°C and winter lows of ?120°C, Mars sounds far too cold for humans. However, thermometer readings from Mars are highly misleading to terrestrials who base their expectations of thermal comfort on their experience in Earth's much thicker atmosphere. The two-planet model of windchill described here suggests that Martian weather is much less dangerous than it sounds because in the meager atmosphere of Mars, convection is a comparatively feeble heat transfer mechanism. The windchill on Mars is expressed as the air temperature on Earth that produces the same cooling rate in still air, in Earth's much denser atmosphere. Because Earth equivalent temperature (EET) is identical to the familiar wind chill equivalent temperature (WCET) that is broadcast across much of North America in winter, it provides a familiar context for gauging the rigors of weather on another planet. On Earth, WCET is always lower than the air temperature, but on Mars the equivalent temperature can be 100°C higher than the thermometer reading. Mars is much colder for thermometers than for people. Some frontier areas of Earth are at least as cold as midlatitude Mars is, year round. Summer afternoons in the tropics of Mars might even feel as comfortable as an average winter day in the south of England. Sunshine on Mars should be about as warm as it is on Earth. Heat balance and clothing emissivity are also briefly discussed.