Collisionless reconnection in Jupiter's magnetotail

We present the first quantitative study of collisionless reconnection in Jupiter's magnetotail. Recently it has been shown that collisionless reconnection can occur in the Earth's magnetotail quasi-neutral sheet when the electrons are subject to chaotic pitch angle diffusion. This happens when the magnetic field is very taillike, i.e., when the curvature parameter κ_e = B_z/B₀(L_z/ρ_e0)^1/2 decreases to ≈ 1.6. For Jupiter's magnetotail, a self-consistent axisymmetric equilibrium model is used to compute the magnetic field and κ_e, and it is found that the condition for electron chaotization is satisfied in a region large enough to allow the growth of a tearing instability. The favourite site for reconnection is situated at about 60 R_J, and the growth time is estimated to be about 370 s, i.e., much shorter than the plasma transit time through the chaotization region. The inductive e.m.f. along a 20 R_J X line is estimated to be of order 100kV - 1 MV, and should accelerate the ions dawnward and the electrons duskward.