Sband radio occultation measurements of the atmosphere and topography of Mars with Mariner 9: Extended mission coverage of polar and intermediate latitudes

A set of significant S band radio occultation measurements was obtained with Mariner 9 during May and June of 1972, for the first time yielding extensive occultation data on the north and south polar regions. The daytime temperature profiles, representative of a clear atmosphere, exhibit gradients (averaging −2.3°K/km) far smaller than those expected under conditions of radiative-convective balance. The measured gradients are in good agreement with those computed for Stone's radiative dynamical models. The near-surface temperatures (180°–190°K) measured in the Martian spring daytime on the north polar cap indicate that it may, at least in part, consist of water ice. Temperatures in the south polar area, measured in nighttime, were low enough for condensation of carbon dioxide to take place. Measurements of the height of the daytime ionosphere at solar zenith angles greater than 72° are lower than the expected heights of the ionization peak, possibly indicating about 25% cooling of the lower atmosphere between November and December of 1971 and May and June of 1972. Planetary radii obtained at latitudes ranging from +86° to −80° indicate a pronounced north-south asymmetry. The south polar region is higher than the north polar area by an average of about 3.4 km; the entire southern hemisphere is 3–4 km higher than the northern hemisphere. A measurement was obtained near the summit of Middle Spot (Pavonis Lacus) showing it to rise about 13.5 km above the surounding terrain.