  A recently published, new analysis of current sheets updated the classic
Harris 1D static solution by considering multiple classes of charged particle
trajectories in a generalized dynamic current sheet. It used a 1D PIC
simulation to describe dynamic pinching and bifurcation of the sheet. These 1D
results strongly suggest that plasma beta or other properties of the inflowing
plasma have a strong effect on the equilibrium thickness of the pinched current
sheet, but cannot describe magnetic reconnection. The time appears right to
carry such 1D studies over to 3D simulations where current sheet thickness has
been found exert an enabling or disabling influence on reconnection. The
Magnetospheric Multiscale Mission (MMS), with its well-resolved multipoint
measurements, has found that reconnection is enabled in collisionless plasma by
non-adiabatic motions of electrons that can only occur in narrow magnetic
structures with a scale comparable to electron inertial lengths (de). The
recent 1D studies strongly suggest that a pinch to such scales can only occur
for inflowing magnetized plasmas with relatively low plasma beta. We conclude
that a parametric exploration of 3D simulated and observed inflow conditions,
especially plasma beta, should shed light on the enablement of reconnection in
collisionless plasmas.
