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Saturn Kilometric Radiation (SKR), being the dominant radio emission at Saturn, has been extensively investigated. The low‐frequency extension of SKR is of particular interest due to its strong association with Saturn's magnetospheric dynamics. However, the highly anisotropic beaming of SKR poses challenges for observations. In most cases, the propagation of SKR is assumed to follow straight‐line paths. We explore the propagation characteristics of SKR across different frequencies in this study. An extended equatorial shadow region for low‐frequency SKR is identified, resulting from the merging of the Enceladus plasma torus and the previously known equatorial shadow zone. Ray‐tracing simulations reveal that low‐frequency (≲$\lesssim $100 kHz) SKR is unable to enter the shadow region and is instead reflected toward high latitudes. In contrast, high‐frequency SKR (≳$\gtrsim $100 kHz) generally propagates without hindrance. Observations suggest that some low‐frequency SKR can enter the shadow region through reflection by the magnetosheath or leakage from the plasma torus. Saturn Kilometric Radiation (SKR) is a natural electromagnetic wave generated in Saturn's high‐latitude region along its magnetic field lines. Variations in SKR frequency could offer insights into Saturn's magnetic conditions, especially its interaction with the solar wind. However, the observed frequency characteristics of SKR depend on viewing geometry due to its directional nature. While past studies assumed SKR travels in straight lines, this may not hold true for low‐frequency SKR. These emissions can change direction when they encounter dense plasma, similar to light reflecting off a mirror or bending when entering water. At Saturn's equatorial region, the plasma torus created by Enceladus, one of Saturn's moons, contains dense plasma and significantly affects radio wave propagation. Our study investigates the distribution of SKR at different frequencies and identifies a shadow region where low‐frequency SKR emissions are rarely seen. Using numerical simulations of ray propagation paths, we discover that low‐frequency SKR emissions cannot reach these shadow regions because they are reflected by the dense plasma torus. However, occasionally, we observe low‐frequency SKR in the shadow region, suggesting the possibility of reflection by Saturn's magnetosheath or leakage through the plasma torus. The propagation characteristics of Saturn Kilometric Radiation (SKR) are established statistically and by ray‐tracingA shadow region of the low‐frequency SKR near the equatorial region at large radial distances is discovered and discussedLow‐frequency SKR may enter the shadow region due to torus leakage or reflection at the magnetosheath The propagation characteristics of Saturn Kilometric Radiation (SKR) are established statistically and by ray‐tracing A shadow region of the low‐frequency SKR near the equatorial region at large radial distances is discovered and discussed Low‐frequency SKR may enter the shadow region due to torus leakage or reflection at the magnetosheath

Since the discovery of Jovian auroral radio emissions, the question arises of the source positions of the different components (broadband kilometric, hectometric, and decametric) and their association with far ultraviolet (FUV) auroral emissions. We surveyed Juno's first 15 perijoves to track local radio sources from in situ Juno/Waves measurements (50 Hz to 40 MHz). This allowed us to study the 3‐D spatial distribution of the broadband kilometric, hectometric, and decametric radio sources. These sources are carried by the same magnetic field lines, with the bulk of them at apex M ranging from 15 to 60 (distance measured in RJat the magnetic equator). Finally, comparisons with images of the Jovian FUV aurorae simultaneously acquired by the Hubble Space Telescope (HST) reveal a partial spatial colocation of the FUV main oval emission with the identified local radio sources. Jupiter produces auroral emission at radio and far ultraviolet (FUV) wavelengths. These emissions have been studied for more than half a century, from an equatorial point of view. The Juno spacecraft, in orbit around Jupiter since July 2016, passes above the northern and southern poles once per orbit, and thus inside the regions where the auroral radio emission occurs. Using the first 15 Juno's orbits, we found that the sources, from the kilometer to the decameter wavelengths, are all colocated. The comparison with simultaneous images on the FUV wavelengths, acquired by the Hubble Space Telescope, reveals that the source of Jovian auroral radiation at the kilometer and decameter wavelengths are magnetically connected to region of FUV emissions. The position of the sources of the broadband Kilometric, Hectometric and Decametric auroral radio emissions is statistically determined from in situ source crossings by Juno/WavesAll radio sources are found to be located on the same set of magnetic field lines, with M ranging from 10 to 60, and are connected to the main UV ovalCorrespondence between auroral radio and ultraviolet emissions validated by simultaneous auroral observations by Juno/Waves (radio) and HST/STIS (FarUltraviolet)

Observations of Jovian broadband kilometric (bKOM) radiation and ultraviolet (UV) auroras were acquired with the Waves and Juno‐UVS instruments for ∼2 hr over the northern and southern polar regions during Juno's perijoves 4, 5, and 6 passes (PJ4, PJ5, and PJ6). During all six time periods, Juno traversed auroral magnetic field lines connecting to the UV main auroral ovals, matching the estimates of bKOM radio source footprints. The localized bKOM radio sources for the PJ4 north pass map to magnetic field lines having distances of 10 to 12 Jovian radii (RJ) at the magnetic equator, whereas the extended bKOM radio sources for the other events map to field lines extending to 20–61 RJ. We found the peak bKOM intensities during Juno's potential radio source crossings show positive, negative, and no correlations with the UV main oval brightness and color ratio. Only the positive correlations suggest wave‐particle energy transport. Jupiter's polar auroras show complex emissions at radio and ultraviolet (UV) wavelengths. However, understanding these two phenomena and how they interact has been hindered by poor visibility of these observations from Earth or near‐equator spacecraft and insufficient spatial resolution of the Jovian radio images. Since 5 July 2016, the Juno spacecraft has toured Jupiter as its first polar explorer in a 53‐day eccentric orbit. One of Juno's main goals is to survey Jupiter's complex auroral regions at both poles. Using the first concurrent radio‐UV aurora observations of both north and south hemispheres during three closest approaches to the planet, we found that the source locations of Jovian auroral radiation at the kilometer wavelengths (broadband kilometric radiation) are magnetically connected to regions of bright UV emissions on the main auroral oval. For some events, the UV auroral intensity positively correlates with broadband kilometric radio intensity. Juno's vantage point of Jovian auroras at radio and UV wavelengths yields a better understanding of the auroral processes at different altitudes. First simultaneous observations of Jovian broadband kilometric radio source footprints and ultraviolet auroras were carried out using JunoJovian broadband kilometric radio source footprints correspond to the UV main oval locationsLink of Jovian radio intensity during Juno's near‐source crossing with both brightness and color ratio of the UV main oval was investigated

Throughout 2017, the Hubble Space Telescope (HST) observed the northern far‐ultraviolet aurorae of Saturn at northern solstice, during the Cassini Grand Finale. These conditions provided a complete viewing of the northern auroral region from Earth and a maximal solar illumination, expected to maximize the ionosphere‐magnetosphere coupling. We analyze 24 HST images concurrently with Cassini measurements of Saturn's kilometric radiation and solar wind parameters predicted by two magnetohydrodynamic models. The aurorae reveal highly variable components, down to timescales of minutes, radiating 7 to 124 GW. They include a nightside‐shifted main oval, unexpectedly frequent and bright cusp emissions, and a dayside low‐latitude component. On average, these emissions display a strong local time dependence with two maxima at dawn and premidnight, the latter being newly observed and attributed to nightside injections possibly associated with solstice conditions. These results provide a reference frame to analyze Cassini in situ measurements, whether simultaneous or not. In 2017, the Hubble Space Telescope regularly observed the northern ultraviolet aurorae of Saturn in coordination with Cassini in situ measurements obtained during the Grand Finale, when the spacecraft flew across magnetic field lines connected to the aurorae. Hubble imaged Saturn's aurorae at 24 occasions spread over 7 months during northern solstice, when the northern auroral region was both fully visible from Earth and permanently illuminated by the Sun. The observed aurorae display a variety of components observed poleward of 68° latitude with different properties, some of which were unreported before. These emissions strongly vary with time, down to a few minutes, and radiate from 7 to 124 GW. On average, the auroral intensity also strongly varies with local time (a Sun‐referenced frame) and peaks at dawn, as previously observed, and also premidnight, pointing to a recurrent nightside activity of the magnetosphere. These results provide a reference basis to analyze Cassini in situ measurements. Saturn's northern UV aurorae at solstice were sampled from HST observations coordinated with Cassini's Grand FinaleThe observed aurorae are highly variable with powerful events, radiating up to 124 GW, controlled by solar wind and planetary rotationThe average auroral brightness strongly varies with LT with two maxima at dawn (previously known) and premidnight (newly identified)

We compare observations from the Juno/Waves radio experiment with simulations of radio «arcs» in the time‐frequency plane resulting from the Io‐Jupiter interaction, performed with the ExPRES code. We identify the hemisphere of origin of the observed arcs directly from simulations and confirm this identification through comparison with Juno, Nançay, and Wind observations. The occurrence and shape of observed arcs are well modeled, at low latitudes with their usual shapes as seen from Earth, as well as at high latitudes with longer, bowl‐shaped, arcs observed for the first time. Predicted emission is actually observed only when the radio beaming angle θ= (k,B) ≥ 70° ± 5°, providing new constraints on the generation of the decameter emission by the Cyclotron Maser Instability. Further improvements of ExPRES are outlined, which will then be applied to Juno and Earth‐based observations of radio emissions induced by other Galilean satellites or associated to the main auroral oval. First Juno/Waves observations compared to ExPRES simulations of Jupiter‐Io decametric emissionNear equator ExPRES simulations show that most of the arcs observed in the time‐frequency plane by Juno, Wind, and Nançay are due to IoThe simulations and observations of Io arcs are in good agreement when the modeled radio beaming angle θ= (k,B) ≥ 70° ± 5°

Juno's first perijove science observations were carried out on 27 August 2016. The 90° orbit inclination and 4163 km periapsis altitude provide the first opportunity to explore Jupiter's polar magnetosphere. A radio and plasma wave instrument on Juno called Waves provided a new view of Jupiter's auroral radio emissions from near 10 kHz to ~30 MHz. This frequency range covers the classically named decametric, hectometric, and broadband kilometric radio emissions, and Juno observations showed much of this entire spectrum to consist of V‐shaped emissions in frequency‐time space with intensified vertices located very close to the electron cyclotron frequency. The proximity of the radio emissions to the cyclotron frequency along with loss cone features in the energetic electron distribution strongly suggests that Juno passed very close to, if not through, one or more of the cyclotron maser instability sources thought to be responsible for Jupiter's auroral radio emissions. First polar view of Jupiter's auroral radio emissionsEmissions composed of multiple V‐shaped spectral featuresJuno passed close to or through five or more source regions

Two well‐defined Jovian decametric radio arcs were observed at latitudinal separations of 11°–16° from the Juno spacecraft near Jupiter and the Nançay Decameter Array (NDA) at Earth on 17 May and 25 August 2016. These discrete arcs are from the so‐called A source covering both Io‐related and non‐Io‐related emissions. By measuring the wave arrival time at two distant observers with propagation time correction, the remaining delay times are 92.8 ± 1.3 min for the first arc and 116.0 ± 1.2 min for the second arc. This implies that both radio sources are not controlled by the orbital motion of Io but Jupiter's rotation itself. The geometrical information for Juno and NDA and the loss cone‐driven electron cyclotron maser instability theory provide these radio sources that are located at about 173° ± 10° in system III longitude projected onto Jupiter's north surface and imply resonant electron energy ranges from 0.5 to 11 keV. Two decametric (DAM) arcs were observed from widely spaced latitudes by Juno and NDADirect evidence of long‐lasting DAM arcs corotating with Jupiter is presentedThe loss cone‐driven CMI theory of fundamental X‐mode emission provides a constraint of the concurrent arcs