The structure of the Venusian current sheet

摘要

We investigate the current sheet (CS) of the Venusian magnetotail using the data collected by the Venus Express mission in 2006-2010. We have found that the observed profiles of the main magnetic field component B_x have single-scale or double-scale structures. For single-scale CSs the B_x profile is well approximated by the Harris model, B_0 tanh(t/T_0) (T_0 is the characteristic temporal scale, B_0 is the magnetic field at the CS boundary). For double-scale CSs the B_x profile is better described by the double-scale model, B_1 tanh(t/T_1)+B_2 tanh(t/T_2) with B_2 ＞ 0.3B_0 and T_2 ＞ 2T_1. The magnetic field component perpendicular to the CS plane and the shear component are on average uniform across CSs and ten times smaller than the amplitude of B_x. The observed B_x profiles can be described by the quasiadiabatic CS model. According to our interpretation the electric current in single-scale CSs is generally carried by protons on transient orbits. In double-scale CSs the current density is provided by transient protons and oxygen ions. In this case, the inner CS scale is supported by the proton population, while the outer scale is supported by the oxygen population. We suggest that the Venusian CS thickness is likely several ion thermal gyroradii.