On asymmetry of magnetic activity and plasma flow temperature in Jupiter’s magnetosphere

Abstract

Discs of plasma around giant planets are natural laboratories that contain within mechanisms of transferring and keeping energy into the plasma and magnetic field system. Various missions to Jovian planets observed that expansion of plasmadiscs is not adiabatic and plasma temperature is increasing with radial distance. Magnetometer measurements from Juno mission were examined to determine plausibility of turbulent fluctuations as the plasma heating mechanism. Extensive azimuthal map of magnetic activity in Jupiter’s nightside plasmadisc is presented. Observations show that magnetic activity is distributed asymmetrically, with active and quiet regions. This is similar to the asymmetrical distribution of activity observed in Saturn’s magnetosphere. However, comprehensive study of temperature measurements showed that the only systematic change of temperature in magnetospheres of giant planets is in the radial direction. Observed breakfrequency in the magnetometer time series is systematically greater than the ion cyclotron frequency. Examination of the power spectrum points to that the kinetic energy of the corotating plasma as a source of increase of plasma temperature. This study shows that turbulent fluctuations themselves are not good candidates as a plasma heating mechanism. External pressure fluctuation however, can be used to convert kinetic energy of the plasma flow into thermal.