![]() This intensely bone-chilling image of Mars could become a psychological barrier to potential colonists, as well as to public support for such ventures. ![]() We can only try to imagine how cold the abysmally low temperatures of Mars might feel, especially when combined with high speed winds that sometimes scour the planet. The mean annual temperature of Mars is −63☌ ( Tillman 2009) compared to +14☌ on Earth ( NASA 2010). ![]() No place on Earth experiences the low temperatures that occur every night on Mars, where even in the tropics in summer the thermometer often reads close to −90☌ and, in midlatitudes in winter, as low as −120☌. One such dragon must surely be its weather, for Mars sounds far too cold for human life. The dragons of Mars are daunting logistical and safety challenges that deter human exploration. One of its themes is that Mars is beset by dragons of the sort that ancient mapmakers used to draw on maps in unexplored areas. The groundbreaking book The Case for Mars ( Zubrin 1996) advocates human exploration and colonization of the red planet. Heat balance and clothing emissivity are also briefly discussed. Sunshine on Mars should be about as warm as it is on Earth. Summer afternoons in the tropics of Mars might even feel as comfortable as an average winter day in the south of England. Some frontier areas of Earth are at least as cold as midlatitude Mars is, year round. Mars is much colder for thermometers than for people. On Earth, WCET is always lower than the air temperature, but on Mars the equivalent temperature can be 100☌ higher than the thermometer reading. 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. 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. 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. 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. With an average temperature of −63☌ and winter lows of −120☌, Mars sounds far too cold for humans.
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