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Magnetosphere-ionosphere-thermosphere at the outer planets
Magnetosphere-ionosphere-thermosphere at the outer planets
Licia C. Ray, Lancaster University
Jupiter and Saturn host some of the most brilliant aurorae in the Solar System. Omnipresent, yet variable in intensity and planetographic extent, these emissions are just one sign of magnetosphere-ionosphere-thermosphere (MIT) coupling between giant planets and their surroundings. These rapidly rotating planets are coupled to their surrounding plasma discs through their planetary magnetic fields, which mediate the exchange of angular momentum and energy through a complex system of currents. Lorentz forces, Joule heating, and precipitating particles associated with MIT coupling modify the underlying atmosphere and affect magnetospheric flows. In the magnetosphere, angular momentum drawn from each planet accelerates plasma as it is transported away from its source location, predominately Io at Jupiter and Enceladus at Saturn. Alfvén waves and quasi-static electric fields associated with MIT coupling accelerate particles into the planetary atmospheres, generating auroral emission. Energy is also deposited into the thermosphere through Joule heating associated with corotation enforcement currents. However, questions remain as to how this energy is redistributed across the planets to produce the observed thermospheric temperatures, which exceed predictions by 100s of Kelvin. This tutorial talk reviews the current understanding of MIT coupling at the outer planets, focusing primarily on the Jovian system in light of recent advances in understanding from Juno.
The Io torus and highlights from 10 years operation of the Hisaki mission
The Io torus and highlights from 10 years operation of the Hisaki mission
Kazuo Yoshioka, University of Tokyo
The Io plasma torus (IPT), located in the Jovian inner magnetosphere (6-8 RJ from the planet), is filled with electrons and heavy ions such as sulfur and oxygen, a significant portion of which originates from the volcanoes on Io. The IPT serves as a crucial region connecting the primary plasma source (Io) with the middle and outer magnetosphere, where highly dynamic phenomena occur. Understanding the behavior of plasma in the IPT is essential for discussing the plasma dynamics in the whole Jovian magnetosphere. A comprehensive understanding of the IPT can be achieved through spectral analysis of ion emissions, which are generated by electron impact excitation. This method is called 'plasma diagnostics.' The emission lines from ions in the IPT are mainly in the extreme ultraviolet (EUV) region. Therefore, EUV spectroscopic data are important for the study of Jupiter’s inner magnetosphere. Hisaki, an Earth-orbiting spacecraft equipped with the extreme ultraviolet spectroscope EXCEED, has been providing high-resolution spectra of the IPT from 2013 to 2023. Here we present a summary of 10 years of operations for IPT spectroscopic observation by Hisaki. Ion and electron density variation, the relationship between the IPT and auroras, and responses to volcanic activity will be discussed.
Ice Giant Magnetospheres
Ice Giant Magnetospheres
Carol Paty, University of Oregon
The Ice Giant Magnetospheres provide some of the most interesting natural laboratories for studying the influence of large obliquities, rapid rotation, highly asymmetric magnetic fields, and large Alfvénic and sonic Mach numbers on magnetospheric processes. Uranus is subjected to extreme seasonal variations resulting from the nearly 98° tilt of its rotation axis. At both Uranus and Neptune, the solar wind-magnetosphere interaction varies dramatically on diurnal and seasonal timescales due to the apparent offset and large tilt of the dipole field. With in situ observations limited to a single encounter by the Voyager 2 spacecraft, a growing number of analytical and numerical models have been put forward to characterize ice giant magnetospheres and test hypothesis related to magnetospheric boundary layers, the solar wind interaction, the formation of the radiation belts, understanding charged particle precipitation, aurora, and energy deposition to the atmosphere, and quantifying potential plasma sources and the distribution of plasma observed. Yet despite these recent studies, many questions regarding the observations of the Ice Giant magnetospheres remain unanswered. This has led to great community interest in revisiting these distant worlds, with the Decadal Survey placing the Uranus Orbiter and Probe (UOP) as the highest flagship mission priority, and the Planetary Mission Concept Study Neptune Odyssey receiving tremendous support as well. In this tutorial I will describe the current understanding of the ice giant magnetosphere, as well as the key magnetospheric science questions motivating the UOP mission.
Radiation Belts of the Outer Planets
Radiation Belts of the Outer Planets
Peter Kollmann, Johns Hopkins University Applied Physics Laboratory
Planets with an intrinsic magnetic field trap and accelerate charged particles, and form radiation belts. These belts exist in a permanent interplay of different physical processes: Particles are initially provided, e.g., through erupted moon material, and accelerated to high energies, e.g., through transport into the stronger parts of the planet’s magnetic field. Particle production is countered through the removal of particles, e.g., when they hit the planet. Particle acceleration in turn is balanced through slowing the particles down again, e.g., when emitting synchrotron radiation. The balance of the involved processes determines the structure and dynamics of the various radiation belts. This presentation will discuss the processes that are currently considered as most important at Jupiter and Saturn, and illustrate them through examples. We will briefly review the current state of the relative importance of these processes, although that topic is far from being closed, even at well-explored planets. Comparison with Earth will provide context and demonstrate how some physical processes are potentially better studied at one planet than another. We will discuss some of the limited data we have for the radiation belts of the moon Ganymede, as well as the Ice Giants. While these data are far from conclusive, they reveal open questions or even mysteries that are left for future missions, such as JUICE or an Ice Giant flagship. We will discuss how the study of radiation belts also has an impact on several other fields of planetary science and, e.g., how it informs on ring structure.
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