Weather Report from Mars

Mars has an atmosphere; therefore it must have weather. Starting with this thesis--as thin as the Martian atmosphere itself--Seymour L. Hess of Lowell Observatory, Flagstaff, Ariz, set out to chart Martian weather. He reports his findings in the current Sky and Telescope.

Even through a large telescope, Mars looks like a small reddish disc doing a slightly hysterical dance. But delicate instruments can measure with fair accuracy on its barren surface the temperature of spots as small as 400 miles wide. Since differences of temperature (which make an atmosphere circulate) are the basic cause of weather, measurements of temperature can be translated into a crude weather map.

Using the best data he could find, Hess drew a temperature map for Mars. It turned out to look much like a terrestrial temperature map. In its "winter" hemisphere, Mars was deathly cold (about 40DEG below zero Fahrenheit at Lat. 50) and showed no sudden changes of temperature. Near the equator the temperature on Hess's map averaged 50DEG F. and in the sunny "summer" hemisphere there were two hot spots where Martian thermometers, if any, stood at 86DEG F.

Such temperature variations, Hess reasoned, ought to stir up the Martian atmosphere as they do the earth's. For proof that they actually do, he turned to observations of the faint white clouds that sometimes drift across the red surface of Mars. The clouds indicated that Mars, like the earth, has "prevailing westerlies" as well as winds circulating around areas of high or low pressure. He thinks that the lot spots are probably "heat lows" like those that often form in summer in the U.S. southwest.

To judge by Hess's analysis, Martian weather is pretty dull. If an earthling on Mars were able to breathe its atmosphere (containing little oxygen), he would see few clouds the year round. The wind might push him about a bit, but he would not have to worry about rain or snow. His worst problem would be the more extreme contrast between winter and summer. The Martian year (almost twice as long as the earthly year) allows Mars more time to heat up in summer, cool off in winter.

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