Axial precession of Mars, illustration. The precession of a rotating body (such as a planet) is a gradual change in its orientation. Here, this is seen as a change in the orientation of the axial tilt. At top, the axis is tilted in a particular direction. At bottom, this axial tilt has reversed. The axial precession of Mars takes place over a period of 175,000 Earth years, much slower than the change in the Earth's axial tilt.