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Magnetic Dipolarization, a hallmark indicator of the formation of field‐aligned currents, plays a crucial role in the energy dissipative processes that occur within planetary magnetospheres. Saturn's magnetic dipolarization was found to recur after one planetary rotation, suggesting a potential correlation with the corotating current systems. The observation of enhanced Energetic Neutral Atoms (ENA) within Saturn's inner magnetosphere serves as a diagnostic tool, revealing the existence of a rotating, dynamic Partial Ring Current (PRC) system. By utilizing multiple datasets from Cassini, this study advances the understanding of the interrelationship between ENA emission and magnetic dipolarization. Our results suggest the possibility of a coupling between the PRC system revealed by the ENA emission and magnetic dipolarization. Furthermore, a temporal correlation was found between the ENA emissions and two distinct radio emissions. This study discusses potential causal relationships among these phenomena and first time proposes a global unified physical picture.

We study the effect of negatively charged dust on the magnetic-field-aligned polarisation electrostatic field (E-parallel to) using Cassini's RPWS/LP in situ measurements during the `ring-grazing' orbits. We derive a general expression for E-parallel to and estimate for the first time in situ parallel to E-parallel to parallel to (approximately 10(-5) V m(-1)) near the Janus and Epimetheus rings. We further demonstrate that the presence of the negatively charged dust close to the ring plane (vertical bar Z vertical bar less than or similar to 0.11 R-s) amplifies parallel to E-parallel to parallel to by at least one order of magnitude and reverses its direction due to the effect of the charged dust gravitational and inertial forces. Such reversal confines the electrons at the magnetic equator within the dusty region, around 0.047 R-s above the ring plane. Furthermore, we discuss the role of the collision terms, in particular the ion-dust drag force, in amplifying E-parallel to. These results imply that the charged dust, as small as nanometres in size, can have a significant influence on the plasma transport, in particular ambipolar diffusion along the magnetic field lines, and so their presence must be taken into account when studying such dynamical processes.

Stunning aurorae are mainly produced when accelerated electrons travel along magnetic field lines to collide with the atmosphere. The motion of electrons often corresponds to the evolution of a magnetic field-aligned current system. In the terrestrial magnetosphere, the current system is formed at the night-side sector, and thus produces an auroral bulge at night. Due to the different energy sources between Saturn and the Earth, it is expected that their auroral current systems are fundamentally different, although the specific auroral driver at Saturn is poorly understood. Using simultaneous measurements of the aurora, particles, magnetic fields, and energetic neutral atoms, we reveal that a chain of paired currents, each of which includes a downward and an upward current branch, is formed in Saturn's magnetosphere, which generates separated auroral patches. These findings inform similar auroral current structures between the Earth and Saturn, while the difference is that Saturn's unique mass and energy sources lead to a rotational characteristic.

The Juno spacecraft entered orbit at Jupiter on July 5, 2016. Since then, Juno has orbited Jupiter in high inclination orbits, crossing the ring plane near perijove. During 20 of the first 21 crossings, the Waves instrument detected signals associated with dust impacts. The impact rate profiles show peaks of order 6 s‐1 around the ring plane with half width at half maximum ~2000‐3000 km. The polarity ratio of the impact signals didn't follow the areas of the antennas exposed to dust impacts that change due to the rotation of the spacecraft, suggesting Waves detects impacts on the Juno spacecraft and not just on the Waves antennas. The impact rate profile changed during Perijove 19, when the spacecraft rotation axis was tilted to the south, increasing the area of the solar panels exposed to impacts, indicating that the detected impacts were on the spacecraft body. Grain sizes of order 1 μm are estimated, and the differential size distribution has a slope of ‐5.1 and with number densities of order 3 x 10‐6 m‐3.

We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in situ measurements of magnetic field, particles, and radio waves from the Juno Spacecraft in the outer magnetosphere, from ~ 80RJ to 60RJ during 17 to 22 March 2017. Two cycles of accumulation and release of magnetic flux, named magnetic loading/unloading, were identified during this period, which correlate well with electron energization and auroral intensifications. Magnetic reconnection events are identified during both the loading and unloading periods, indicating that reconnection and unloading are independent processes. These results show that the dynamics in the middle magnetosphere are coupled with auroral variability.

We present simultaneous observations of aurorae at Jupiter from the Hubble Space Telescope and Hisaki, in combination with the in situ measurements of magnetic field, particles, and radio waves from the Juno Spacecraft in the outer magnetosphere, from ~ 80RJ to 60RJ during 17 to 22 March 2017. Two cycles of accumulation and release of magnetic flux, named magnetic loading/unloading, were identified during this period, which correlate well with electron energization and auroral intensifications. Magnetic reconnection events are identified during both the loading and unloading periods, indicating that reconnection and unloading are independent processes. These results show that the dynamics in the middle magnetosphere are coupled with auroral variability.

Dust particles in the Saturn system can be detected by the Radio and Plasma Wave Science (RPWS) instrument on board Cassini via antenna voltage signals induced by dust impacts. These impact signals have been simulated in the laboratory by accelerating dust particles onto a Cassini model with electric field antennas. RPWS dust measurements have been shown to be consistent with the Cosmic Dust Analyzer. During the Grand Finale orbits, Cassini flew through the gap between the D ring and Saturn's atmosphere 22 times. In situ measurements by RPWS helped quantify the hazards posed to the spacecraft and instruments on board, which showed a micron-sized dust density orders of magnitude lower than that observed during the Ring Grazing orbits. Close inspection of the waveforms indicated a possible dependence of the impact signal decay time on ambient plasma density. Plain Language Summary Cassini flew through the gap between Saturn and its rings for 22 times before plunging into the atmosphere of Saturn, ending its 20-year mission. The radio and plasma waves instrument on board Cassini helped quantify the dust hazard in this previously unexplored region. The measured density of large dust particles was much lower than expected, allowing high-value science observations during the subsequent Grand Finale orbits.

The role of Z-mode emission in the diffusive scattering and resonant acceleration of electrons is believed to be important at Saturn. A survey of the 5kHz component of this emission at Saturn earlier reported strong intensity in the lower density regions where the ratio of plasma frequency to cyclotron frequency, f(p)/f(c)<1. At Saturn this occurs along the inner edge of the Enceladus torus near the equator and at higher latitudes. Using the Cassini Radio and Plasma Wave Science instrument observations during the Cassini proximal orbits, we have now identified these emissions extending down to and within the ionosphere. Wave polarization measurements and unique frequency cutoffs are used to positively identify the wave mode. Analogous to the role of whistler mode chorus at Earth, Saturn Z-mode emissions may interact with electrons contributing to the filling or depleting of Saturn's inner radiation belts.

Similar to whistler mode chorus, Z-mode emission is an efficient diffusive scatterer of electrons possibly resulting in resonant acceleration. We present results of a survey of both the low-band (5 kHz) and for the first time the high-band (20 kHz) intensity of these emissions, based on over 11 years of Cassini Radio and Plasma Wave Science instrument data including nine ring-grazing orbits and two proximal orbits, which occurred at the end of the mission. We distinguish these emissions using density and polarization measurements and calculate the mean intensity as a function of frequency and spatial coordinates. We find that the average low-band Z-mode intensity peak is P-0 similar to 7 x 10(-8) nT(2), while the high-band peak is much lower at P-0 similar to 10(-9) nT(2). The spatial distribution of intensity differs for each emission band implying different source regions and perhaps different source mechanisms. Plain Language Summary Intense narrow band waves (Z-mode) are observed at Saturn when the spacecraft is located in regions of relatively low density and high magnetic field. These waves are of special importance because they are not seen at such high intensity or over as large a spatial range at Earth. In addition, these waves are known to be very efficient at accelerating electrons under certain conditions and could be responsible for a portion of the observed radiation belts at Saturn. We present an extensive survey of the observations of Z-mode extending over more than 11 years. The survey includes for the first time both the low and high-frequency emissions and orbits from the Cassini final mission, where these waves were seen at a high rate of occurrence. Contour plots and graphs of wave intensity as a function of radius, latitude, and longitude are shown, which will be of value to scientists who model the dynamic processes controlling the electron population at Saturn.

We report on the electron, ion, and dust number densities and the electron temperatures obtained by the Radio and Plasma Wave Science instruments onboard Cassini during the Ring-Grazing orbits. The numerous ring passage observations show a consistent picture as follows: (1) Beyond 0.1 R-S above and below the equator the electron and ion densities are quasi-neutral with a distribution similar to the one obtained in the plasma disk. (2) A sharp ion density enhancement occurs at vertical bar Z vertical bar < 0.1 R-S, to more than 200 cm(-3) at the equator, while the electron density remains low only to values of 50cm(-3). The electron/ion density ratio is <= 0.1 at the equator. (3) Micrometer-sized dust has also been observed at the equator. However, the region of intense dust signals is significantly narrower (vertical bar Z vertical bar<0.02 R-S) than the enhanced ion density regions. (4) The electron temperature (T-e) generally decreases with decreasing Z with small T-e enhancements near the equator. We show that the dust size characteristics are different depending on the distance from the equator, and the large micrometer-sized grains are more perceptible in a narrow region near the equator where the power law slope of the dust size distribution becomes less steep. As a result, different scale heights are obtained for nanometer and micrometer grains. Throughout the ring, the dominant part of the negative charges is carried by the small nanometer-sized grains. The electron/ion density ratio is variable from orbit to orbit, suggesting changes in the dust charging over time scales of weeks. Plain Language Summary The Radio and Plasma Wave Science instrument onboard Cassini observed a dusty plasma during the Ring-Grazing orbits. Dusty plasma is composed of, in addition to the electrons and ions, charged dust grains, and those grains play an important role in the plasma dynamics. The observed electron, ion, and dust number densities and the electron temperatur

The ionized upper layer of Saturn's atmosphere, its ionosphere, provides a closure of currents mediated by the magnetic field to other electrically charged regions (for example, rings) and hosts ion-molecule chemistry. In 2017, the Cassini spacecraft passed inside the planet's rings, allowing in situ measurements of the ionosphere. The Radio and Plasma Wave Science instrument detected a cold, dense, and dynamic ionosphere at Saturn that interacts with the rings. Plasma densities reached up to 1000 cubic centimeters, and electron temperatures were below 1160 kelvin near closest approach. The density varied between orbits by up to two orders of magnitude. Saturn's A- and B-rings cast a shadow on the planet that reduced ionization in the upper atmosphere, causing a north-south asymmetry.

The Cassini spacecraft's first Grand Finale orbit was carried out in April 2017. This set of 22 orbits had an inclination of 63 degrees with a periapsis grazing Saturn's ionosphere, thus providing unprecedented coverage and proximity to the planet. Cassini's Radio and Plasma Wave Science instrument repeatedly detected intense electrostatic waves and their harmonics near closest approach in the dayside equatorial topside ionosphere. The fundamental modes were found to both scale and trend best with the H+ plasma or lower hybrid frequencies, depending on the plasma composition considered. The fine-structured harmonics are unlike previous observations, which scale with cyclotron frequencies. We explore their generation mechanism and show strong evidence of their association with whistler mode waves, consistent with theory. The possibility of Cassini's presence in the ionosphere influencing the resonance and harmonics is discussed. Given their link to the lower hybrid frequency, these emissions may offer clues to constraining Saturn's ionospheric properties.