The validity of fluid equations as approximation to kinetic equations depends on whether there is a sufficiently accurate closure of the hierarchy of velocity moments of the kinetic equations. We propose to use satellite measurements of particle distribution functions to look for closure relations in the magnetosheath and magnetopause, thereby providing observational evidence for deciding when a fluid plasma model is appropriate for those regions. Those regions are of particular interest because it is known that they are highly turbulent, more turbulent than the solar wind, and it is by no means clear that a turbulent plasma will obey a closed set of fluid equations. Moreover, turbulence in the magnetosheath is a topic of great interest in the space community and it is largely not understood. The plasma there may exhibit several differing turbulent states and it is very important to find out which of these, if any at all, can be described as a fluid.
