Modelling Jupiter's magnetodisc: implications for the Juno mission

Abstract:

Jupiter's magnetosphere is radially stretched in the middle magnetosphere owing to force balance between outward centrifugal, plasma pressure gradient and anisotropy forces, and an inward JxB force associated with an azimuthal current. In this paper we discuss recent modelling of Jupiter's magnetodisc, and discuss the implications for the upcoming Juno mission. In particular, we discuss recent work including anisotropic hot plasma pressure in the computation of the magnetodisc structure. We show that the anisotropy current is comparable to the hot plasma pressure current in the middle magnetosphere between 20-40RJ, and that for reasonable magnetosphere-ionosphere coupling current system parameters, Jupiter’s magnetosphere resides close to the limit of the firehose instability. We further show that, using anisotropic pressure, variations in the hot plasma temperature over the range observed by spacecraft data are sufficient to explain the latitudinal changes in the main oval and Ganymede footprint latitudes observed using the Hubble Space Telescope. Juno will traverse the middle magnetosphere in the early-to-mid interval of the main mission, and will provide direct in-situ measurements of the plasma pressures and flows, along with the magnetic field. Using the magnetodisc model, we provide predictions for Juno observations and discuss how these measurements will further constrain the models.