Internal Structure
Although both Viking landers carried a seismometer on board, there were no seismic data collected. Due to instrument packaging difficulties, the two seismometers were put on the top of the landers. As a result, they became wind gauges instead of instruments to detect Martian quakes. Like all other celestial bodies, therefore, the Martian interior can only be deduced at present from geophysical observations such as mean density and mean radius. It is estimated that Mars has a low density crust about 25-70 km thick.

Beneath the crust, there is a silicate mantle between 1300-1800 km thick. At the center, there is likely an iron-rich metallic core with a radius that may vary from 1500-2000 km. A schematic diagram for the internal structure of Mars is given in Figure 1.12.