Euler angles between the rotating body frame of Mars (axes XYZ) and the inertial frame associated with the mean orbit of Mars of 1980 (axes xyz, the x-axis is in the direction of the ascending node of Mars's orbit over the Earth ecliptic of epoch J2000). The X-axis of the BF is chosen as the prime meridian defined in the IAU convention (Archinal et al. 2018). The spin axis longitude ψ is measured from the x-axis to the autumn equinox, ϕ is measured from the equinox to the X-axis, and the obliquity, ε, is the angle from the z-axis to the Z-axis – or the inclination of the BF equator over the IF xy plane.