Ganymede's Mini-Magnetosphere (2D)

Field & Flow

Ganymede's dipole moment 1.00×

Corotating flow speed 1.00×

Plasma density 1.00×

Magnetosphere State

Pressure-balance standoff

– R_G

Observed deflection radius

– R_G

Gyroradius at boundary

– R_G

Deflected / absorbed

0 / 0

How it works

This is the equatorial-plane cross-section of Ganymede's real 3D dipole field. In that plane the dipole field points purely perpendicular to the page (into/out of it), with magnitude falling off as 1/r³ — exactly like a bar magnet viewed side-on from its magnetic equator. That out-of-plane field is what deflects the incoming Jovian plasma, whose flow and gyration both stay visible in this plane.

B_z(r) = -M / r³           (Ganymede's dipole, r in R_G)
Lorentz force per particle:  F = q v × B   (Boris pusher, no approximation)
Pressure balance:  B_z(R_mp)² / 2 = n·v²   (ram pressure of the flow)
⇒ standoff  R_mp = ( M² / (2·n·v²) )^(1/6)

Every dot is a real charged particle, individually integrated every frame with the Boris algorithm — the same energy-conserving scheme used in production particle-in-cell plasma codes. Nothing about a particle's path is scripted: far from Ganymede a particle flies straight through the uniform flow; close in, the dipole field bends it into a gyration arc, and the boundary where "mostly deflected" turns into "mostly hits the surface" emerges purely from that force law. Compare the observed deflection radius (the closest approach measured directly from surviving trajectories) against the pressure-balance standoff computed from the formula above — in a real magnetosphere the two agree, and they should here too.

Dipole moment — scales Ganymede's own field strength, growing or shrinking the magnetopause cavity.
Flow speed and density — set the ram pressure of the incoming plasma; higher pressure compresses the standoff distance.

Incoming plasma (ion) Deflected Absorbed by surface Pressure-balance standoff