Mariner 9 S-band Martian occultation experiment - Initial results on the atmosphere and topography of Mars.

A preliminary analysis of 15 radio occultation measurements taken on the day side of Mars between 40 deg S and 33 deg S has revealed that the temperature in the lower 15 to 20 km of the atmosphere of Mars is essentially isothermal and warmer than expected. This result, which is also confirmed by the increased altitude of the ionization peak of the ionosphere, can possibly be caused by the absorption of solar radiation by fine particles of dust suspended in the lower atmosphere. The floor of the classical bright area of Hellas was found to be about 6 km below its western rim and 4 km below the mean radius of Mars at that latitude.