20 moment transport equations applicable to low &bgr; plasmas of thermal origin in rotating planetary magnetospheres are presented. An analytic solution is found for a set of simplified equations describing the steady-state transport of collisionless plasma neglecting heat flow effects, which is also known as the double adiabatic situation [chew et al., 1956>. The new element of this analytic solution is a closed form solution for the variation of the parallel flow velocity, u∥, along magnetic field lines. The solution is significantly different from the often used assumption that, in the collisionless regime, the divergence of the parallel flow velocity is negligible (cf. [Burgers, 1969>). It is shown that only T⊥/B remains constant along the field line (as predicted by earlier calculations), while the density, parallel temperature and parallel Mach number vary as n/B∝1/u∥, T∥∝1/u2∥, and M∥∝u2∥, respectively (in contrast to earlier predictions of n/B=const, T∥=const, and M∥=const.). ¿ American Geophysical Union 1991