The linear Vlasov dispersion is solved to reveal the kinetic properties of the mirror mode. The existence of the torsional component of both the magnetic and velocity perturbations are kinetic features that are not explained by MHD theory. A parameter study is then employed to clarify the behavior of these particular components under different plasma conditions. The key parameters are the ion temperature anisotropy and the plasma to magnetic pressure ratio which act in similar ways to control the value of the torsional (or Alfv¿nic) components. Data from the Active Magnetospheric Particle Tracer Explorers mission show that under most magnetosheath plasma conditions the magnetic torsional component is negligible, whereas the velocity one is always larger or comparable to the other components. This experimental illustration also shows that there exist elliptically polarized mirror modes, contrary to what our, and all previous, analytical treatments predict. ¿ 2001 American Geophysical Union