Atmospheric occultations now number several thousand. Accuracies of retrieved surface pressure and temperature are in the range of a few pascals, and one kelvin, respectively. Atmospheric structure is obtained with a vertical resolution of about 0.8 km; recent advances in understanding of diffraction effects in occultation observations are expected to lead to an order of magnitude improvement, however. These observations reveal a number of interesting features including, a near-Chapman ionosphere controlled by solar zenith angle, strong diurnal variations in the lowest 2 km of the summer boundary layer, dynamically forced inversions in the lowest scale height in the northern winter hemisphere, and prominent atmospheric wave structures. Observations are accurately located in planetary radius, allowing study of thermal tides, the thermal wind, and the seasonal cycling of gas between the atmosphere and the polar caps.
Study of the gravity field is based on perturbations to the motion of MGS observed along the line of sight from Earth. Preliminary results provide new, very high quality observations of the northern hemisphere. Early analyses of the tracking data show that they support spherical harmonic models of degree and order 75. Direct observation of the seasonal change in mass of the polar cap is a distinct possibility.
Ancillary obserations include unusual very near forward scattering from the surface of Mars.