Martian Cataclysm: Impact energy analysis in support of the origin of multiple anomolies on Mars (cont.)
by Gary R. Spexarth
6. Reduction of Mars Rotation.
The rotational rate of Mars is slower than predicted when compared to the angular momentum of the rest of the terrestrial planets [4], [8].
Was the energy of impact at the Hellas Basin great enough to actually reduce the rate of spin of the planet?
By calculating the kinetic energy of the rotating Martian lithosphere, we can determine the amount of energy that would be required of the Hellas Impact to significantly reduce the Mars spin rate. Only the thickness of the lithosphere is taken into account since it is the only portion of the planet capable of sustaining load, and thus reacting to the force of impact.
Appendix III derives the equations for, and computes, the energy required to reduce the rotational rate of Mars.
The energy required to reduce the Mars spin rate by 20% (19.5 hr day to the current 24.5 hr. day) is computed to be between 4.42x10^{25} and 9.56x10^{25} Joules (depending on the thickness of lithosphere assumed, 110  260 km). This is only 8% to 18% of the total energy of impact of the Hellas Basin. In other words, there was sufficient amount of energy in the Hellas impact to slow the rate of rotation down by 20%.
Therefore, it can be seen that the Hellas impactor imparted enough energy into the Mars system to substantially reduce its rate of spin.
