Jupiter’s magnetosphere

Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits

Abstract

The Juno spacecraft acquired direct observations of the jovian magnetosphere and auroral emissions from a vantage point above the poles. Juno’s capture orbit spanned the jovian magnetosphere from bow shock to the planet, providing magnetic field, charged particle, and wave phenomena context for Juno’s passage over the poles and traverse of Jupiter’s hazardous inner radiation belts. Juno’s energetic particle and plasma detectors measured electrons precipitating in the polar regions, exciting intense aurorae, observed simultaneously by the ultraviolet and infrared imaging spectrographs. Juno transited beneath the most intense parts of the radiation belts, passed about 4000 kilometers above the cloud tops at closest approach, well inside the jovian rings, and recorded the electrical signatures of high-velocity impacts with small particles as it traversed the equator.

The Juno Mission serves two principal science objectives. The first is to understand the origin and evolution of Jupiter, informing the formation of our solar system and planetary systems around other stars. Servicing this objective, Juno’s measurements of gravity, magnetic fields, and atmospheric composition and circulation probe deep inside Jupiter to constrain its interior structure and composition. The second objective takes advantage of Juno’s close-in polar orbits to explore Jupiter’s polar magnetosphere and intense aurorae. From a vantage point above the poles, Juno’s fields and particles instrumentation gather direct in situ observations of the particle populations exciting the aurora, which are imaged simultaneously by Juno’s ultraviolet (UV) and infrared (IR) imaging spectrographs.

Summary

Juno has provided observations of fields and particles in the polar magnetosphere of Jupiter, as well as high-resolution images of the auroras at UV and IR wavelengths. Although many of the observations have terrestrial analogs, it appears that different processes are at work in exciting the aurora and in communicating the ionosphere-magnetosphere interaction. We observed plasmas upwelling from the ionosphere, providing a mechanism whereby Jupiter helps populate its magnetosphere. The weakness of the magnetic field-aligned electric currents associated with the main aurora and the broadly distributed nature of electron beaming in the polar caps suggest a radically different conceptual model of Jupiter’s interaction with its space environment. The (precipitating) energetic particles associated with jovian aurora are very different from the peaked energy distributions that power the most intense auroral emissions at Earth.