The simulations were run with the fully kinetic Particle-In-Cell code SMILEI. The data presented are normalized using ion-scale quantities. The magnetic field and density are normalized to arbitrary values *B _{0}* and

*n*

_{0}, respectively. We choose

*B*

_{0}and

*n*such that the density and magnetic field are equal to 1on the flowing side of the layer (in our simulations: the right side). The masses and charges are normalized to the proton mass m

_{0}*and charge*

_{p}*e*, time is normalized to the inverse of the proton gyrofrequency ω

_{ci}

^{-1 }=

*m*/

_{p}*eB*and length to the proton inertial length δ

_{i }=

*c*/ω

_{pi}, where

*c*is the speed of light and ω

*=(*

_{pi}*n*

_{0}

*e*/

^{2}*m*ε

_{p}*)*

_{0}^{1/2}is the proton plasma frequency. Velocities are normalized to the ions’ Alfvén velocity v

_{Al}

*= δ*

_{ }_{i}ω

*.*

_{ci}All simulations are initialized with a single layer where density, velocity (directed along the y-direction) and magnetic field (directed along the z-direction) vary along the x direction. This layer is contained in the (x, y) plane in a 2-D domain of size (x

*,y*

_{max}*) = (68, 136)δ*

_{max}_{i}. There are

*n*

_{x}=

*n*

_{y}= 2720 cells in the x and y directions, corresponding to a grid resolution of ∆

_{x}= 0.025 δ

_{i}and ∆

_{y}= 0.05 δ

_{i}. The ion and electron distribution functions are initially composed by 50 macro-particles per cell loaded using Maxwellian distributions. Plasma moments and electromagnetic forces are calculated using second-order interpolation. The time step is calculated using a Courant–Friedrichs–Lewy condition, which in our simulations turns out to be ∆ = 8.4 × 10-4 ω

_{ci}

^{-1}, and the total simulation time is 400 ω

_{ci}^{-1}. A reduced mass ratio

*m*/

_{i}*m*= 25 is used for computational reasons.

_{e}Simulations of a velocity sheer layer with a gradient of density and magnetic field. These simulations aim to reproduce a velocity shear layer on Mercury’s flanks, in the frame of the ESA/JAXA BEpiColombo mission. The magnetic field ratio between both side is fixed at *B*_{1}/*B*_{2}=0.5 for all simulations and the density ratio *n*_{1}/*n*_{2} varies.