In 1966, two Caltech scientists were ruminating on the implications of the thin carbon dioxide (CO2) Martian atmosphere first revealed by Mariner IV, a NASA fly-by spacecraft built and flown by JPL. They theorized that Mars, with such an atmosphere, could have a long-term stable polar deposit of CO2 ice that, in turn, would control global atmospheric pressure.

A new study from Caltech suggests that the theory, developed by physicist Robert B. Leighton (BS ’41, MS ’44, Ph.D. ’47) and planetary scientist Bruce C. Murray, may indeed be correct.

Carbon dioxide makes up more than 95 percent of Mars’s atmosphere, which has a surface pressure of only 0.6 percent that of Earth. One prediction of Leighton’s and Murray’s theory—with enormous implications for  on Mars—is that its atmospheric pressure would swing in value as the planet wobbles on its axis during its orbit around the sun, exposing the poles to more or less sunlight. Direct sunlight on the CO2 ice deposited at the poles leads to its sublimation (the direct transition of a material from a solid to a gaseous state). Leighton and Murray predicted that, as exposure to sunlight shifts, atmospheric pressure could swing from just one-quarter that of today’s Martian atmosphere to twice that of today over cycles of tens of thousands of years.

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