INTERIOR STRUCTURE AND SEASONAL MASS REDISTRIBUTION OF MARS FROM RADIO TRACKING OF MARS PATHFINDER

Doppler and range measurements to the Mars Pathfinder lander made usin g its radio communications system have been combined with similar meas urements from the Viking landers to estimate improved values of the pr ecession of Mars' pole of rotation and the variation in Mars' rotation rate. The observed precession of -7576 +/- 35 milliarc seconds of ang le per year implies a dense core and constrains possible models of int erior composition. The estimated annual variation in rotation is in go od agreement with a model of seasonal mass exchange of carbon dioxide between the atmosphere and ice caps.