Doppler and range measurements to the Mars Pathfinder lander made using its radio
communications system have been combined with similar measurements from the Viking
landers to estimate improved values of the precession of Mars’ pole of rotation and the
variation in Mars’ rotation rate. The observed precession of –7576 6 35 milliarc seconds
of angle per year implies a dense core and constrains possible models of interior composition.
The estimated annual variation in rotation is in good agreement with a model of
seasonal mass exchange of carbon dioxide between the atmosphere and ice caps.