Temperature contrasts between warm tropics and cool high latitudes depends on how efficiently heat is transported by the atmosphere (and oceans) from the tropics. This heat transport is generally assumed to be proportional to atmospheric pressure, but we show with a simple model that this prediction fails by orders of magnitude for Mars and Titan. However, a basic principle, previously postulated for the Earth, does successfully predict the heat flows and zonal temperatures of Mars and Titan. The circulation predicted by this Maximum Entropy Production (MEP) principle is consistent with Titan's observed zonal structure and the winds and CO2 frost cycle on Mars. The principle makes powerful predictions where detailed information is lacking, such as on the early Earth and on possibly habitable extrasolar planets. ¿ 2001 American Geophysical Union