Martian temperatures and thermal properties

Abstract

We have utilized previously unreduced 8–13 μm radiometry of Mars performed in 1954 by Sinton and Strong to obtain the distribution of temperature over the Martian surface. The temperatures are consistent with predictions obtained from solution of the one-dimensional equation of heat conduction with a thermal inertia of about 0.005 cal cm −2 sec − 1 2 deg −1 . This value is also suggested by the mean microwave brightness temperature of about 200°K. At the Martian atmospheric pressure, this inertia would result from average particle sizes of about 100 μm. The thermal inertia of the darkest areas is larger than that of the bright areas, as would be expected if the atmospheric pressure is higher or the mean particle size is larger in the dark areas. The observed latitudinal temperature gradient appears to be consistent with temperatures of approximately 145°K at 60° winter latitudes and therefore with a polar cap composed, at least in part. of CO 2. At all latitudes the minimum temperature falls below 190°K; under these circumstances, a significant fraction of the atmospheric water vapor will condense at night, contributing to the “dawn haze.” An analysis of the microwave spectrum of Mars suggests that the loss tangent of the subsurface material is less than 0.03.