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This review examines ultra-low frequency (ULF) waves across different planetary environments, focusing on Earth, Mercury, and Saturn. Data from spacecraft missions (CHAMP, Swarm, and Oersted for Earth; MESSENGER for Mercury; and Cassini for Saturn) provide insights into ULF wave dynamics. At Earth, compressional ULF waves, particularly Pc3 waves, show significant power near the equator and peak around Magnetic Local Time (MLT) = 11. These waves interact complexly with Alfvén waves, impacting ionospheric responses and geomagnetic field line resonances. At Mercury, ULF waves transition from circular to linear polarization, indicating resonant interactions influenced by compressional components. MESSENGER data reveal a lower occurrence rate of ULF waves in Mercury's foreshock compared to Earth's, attributed to reduced backstreaming protons and lower solar wind Alfvénic Mach numbers, as ULF wave activity increases with heliocentric distance. Short Large-Amplitude Magnetic Structures (SLAMS) observed at Mercury and Saturn show distinct characteristics compared to those of Earth, including the presence of whistler precursos waves. However, due to the large differences in heliospheric distances, SLAMS (their temporal scale size correlate with the ULF wave frequency) at Mercury are significantly shorter in duration than at Earth or Saturn, since the ULF wave frequency primarily depends on the strength of the interplanetary magnetic field. This review highlights the variability of ULF waves and SLAMS across planetary environments, emphasizing Earth's well-understood ionospheric interactions and the unique behaviours observed for Mercury and Saturn. These findings enhance our understanding of space plasma dynamics and underline the need for further research regarding planetary magnetospheres. [ABSTRACT FROM AUTHOR]

This paper presents an innovative approach using Dynamical Systems Theory (DST) for interplanetary orbit insertion into Saturn−Titan three−body orbits. By leveraging DST, this study identifies invariant manifolds guiding a spacecraft into Titan−centered Distant Retrograde Orbits (DROs), strategically selected for their scientific significance. Subsequently, Particle Swarm Optimization (PSO) is employed to fine−tune the insertion parameters, thereby minimizing ΔV. The results demonstrate that the proposed method allows for a reduction in ΔV of over 70% compared to conventional approaches like patched conics−based flybys (2.68 km/s vs. 9.23 km/s), albeit with an extended time of flight, which remains notably faster than weak stability boundary transfers. This paper serves as an interplanetary mission planning methodology to optimize spacecraft trajectories for the exploration of the Saturn−Titan system. [ABSTRACT FROM AUTHOR]

Here we review the origin, evolution, and compositional properties of Saturn's ring moons. This class of eleven small satellites includes objects orbiting near the outer edge of the main rings (Pan, Daphnis, Atlas, Prometheus, Pandora, Janus, Epimetheus) and "ring-embedded" moons (Aegeon, Methone, Anthe, Pallene) orbiting inward of Enceladus and associated with either diffuse or partial rings. We discuss current formation scenarios, according to which ring moons could originate either in the main rings from accretion onto original seeds denser than the ring material, or outside the A ring from spontaneous accretion of ring particles, and then evolve outwards due to gravitational torque from the rings. Remote sensing observations of the ring moons from the Cassini mission are analyzed in the broader context of Saturn's icy moons and main rings observations. Spectroscopic data support a compositional paradigm similar to the main rings, dominated by water ice, and smaller amounts of two separate contaminants, in the form of a UV absorber and a spectrally neutral darkening material. Global radial trends in the spectral properties of the ring moons suggest that the surface composition is significantly affected by a complex interplay of exogenous processes, among which the contamination from nearby A ring particles, meteoritic bombardment, charged particle flux, and E ring particle accumulation, depending on the corresponding magnitude at the ring moon orbital distance and exposure time. These processes modify the original composition inherited by the rings and, coupled with the fact that the surface composition is likely representative only of the ring moon outer layers, make it difficult to trace back the present composition to a given ring moon formation scenario. [ABSTRACT FROM AUTHOR]

Abstract Investigations into quasiperiodic (QP) whistler mode emissions within Saturn's magnetosphere have uncovered distinctive characteristics of these emissions, which display a nearly periodic rising tone structure in the wave spectrogram, characterized by modulation periods of several minutes. These QP emissions are predominantly observed at low L‐shells around 5 and near the magnetic equator. Utilizing a quasi‐linear analysis framework, we evaluate the effects of these waves on the dynamics of energetic electrons. Our analysis suggests that these QP emissions can efficiently cause the loss of electrons within the energy range from 10 to 60 keV over a timescale of tens of minutes. By incorporating these findings into Fokker‐Planck simulations, we find minimal acceleration effects. This study is the first to examine QP emissions and their implications for energetic electron dynamics in Saturn's magnetosphere, highlighting their potentially significant contribution to the magnetospheric processes and dynamics.

Widespread cognitive test screening as part of tele-public health initiatives necessitates a test that is self-administered online and automatically scored, with no clinician effort. The feasibility of unsupervised cognitive screening is unclear. We adapted the Self-Administered Tasks Uncovering Risk of Neurodegeneration (SATURN) to make it suitable for self-administration and automatic scoring. A sample of 364 healthy older adults completed SATURN via a web browser, in a fully independent manner. SATURNs overall score was not modulated by gender, education, reading speed, the time of day at which the test was taken, or an individuals familiarity with technology. SATURN proved extremely portable across operating systems. Importantly, comments from participants reported satisfaction with the experience and the clarity of the instructions. SATURN represents a fast and easy screening tool that can be used for a first assessment, during a routine test or clinical evaluation, or during periodic health monitoring, in person or remotely.

Saturn's atmospheric boreal hexagon, discovered by the Voyager 1 probe in 1981, has such dimensions – sides km. 13800; total extension in length almost km. 30000; latitude 78°N; major angular diameter 4″; smaller angular diameter 1.3″ – to make it visible from Earth with common telescopes. Nowadays it is photographed with instruments with a diameter of 36 cm (Celestron C14) and digital image processing. We therefore wondered in the recent past if it had ever been reproduced in telescopic images prior to 1981. A systematic archive research conducted by us (Walter Ferreri, Mario Codebò, Barbara Bubbi 2021a; 2021b) in the two-year period 2020-2021 allowed us to find old drawings, performed starting from 1898 by the astronomers E.E. Barnard and E.M. Antoniadi with various refractors, in which the hexagon was reproduced although never mentioned in the writings. In the summer of 2022 Henry de Santis then found a drawing by the Italian astronomer Luigi Taffara from 1929 which presents the same reproduction of the hexagon. Two facts are noteworthy: 1) all the reproductions found so far have been copied from images obtained with refractor telescopes of various diameters, but never with reflectors; 2) the dates on the drawings show that the hexagon has persisted on Saturn's north pole since at least 1898. Further research in the archives of the Lowell Observatory, carried out by Laura Citernesi, demonstrated that professional photographs, taken in the first half of the 20th century, consistently did not have sufficient resolving power to show the hexagon. In this article we present and discuss all the images found to date.

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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

The previously unpublished cuneiform fragment BM 47886+47914 belongs to an astral compendium written no later than 140/139 BCE. It contains a rare combination of procedures connected to mathematical astronomy, including a previously unknown one for Mercury's daily motion, and what appear to be astrological procedures. It is argued that the fragment is an indirect join to BM 55555+55562 (ACT No. 210 = BMAPT No. 95), a similar, undated compendium of planetary and lunar procedures, including one mentioning a "year of the Sun," for which a Greek origin has been proposed. BM 47886+47914 preserves a date of writing, with possible implications for the origin of the "year of the Sun." [ABSTRACT FROM AUTHOR]

Two moons of Saturn, Janus and Epimetheus, are in co-orbital motion, exchanging orbits approximately every four Earth years as the inner moon approaches the outer moon and they gravitationally interact. The orbital radii of these moons differ by only 50 km (less than the moons' mean physical radii), and it is this slight difference in their orbits that enables their periodic exchanges. Numerical n-body simulations can accurately model these exchanges using only Newtonian physics acting upon three objects: Saturn, Janus, and Epimetheus. Here we present analytical approaches and solutions, and corresponding computer simulations, designed to explore the effects of the initial orbital radius difference on otherwise similar co-orbital systems. Comparison with our simulation results illustrates that our analytic expressions provide very accurate predictions for the moon separations at closest approach and simulated post-exchange orbital radii. Our analytic estimates of the exchange period also match the simulated value for Janus and Epimetheus to within a few percent, although systems with smaller differences in their orbital radii are less well-modeled by our simple approach, suggesting that either full simulations or more sophisticated analytic approaches would be required to estimate exchange periods in those cases. [ABSTRACT FROM AUTHOR]

Recent observations of Jupiter's atmosphere showing unexpected depletion of ammonia below the ammonia cloud-forming region has brought up the question of whether a single point measurement below the cloud decks in a giant planet atmosphere can provide sufficient information to answer fundamental science questions. We outline here the science questions that can only be answered by in situ observations in the giant planet atmospheres, many of which are location invariant. These questions are identified in the recent planetary science decadal survey as high priority for answering over the next decade. We evaluate the implications of the ammonia observations at Jupiter for the specific measurements needed and demonstrate that they do not invalidate single point measurements made to answer these questions. [ABSTRACT FROM AUTHOR]

Spokes are localized clouds of fine particles that appear over the outer part of Saturn's B ring. Over the course of the Cassini mission, the Imaging Science Subsystem obtained over 20,000 images of the outer B ring, providing the most comprehensive data set for quantifying spoke properties currently available. Consistent with prior work, we find that spokes typically appear as dark features when the lit side of the rings is viewed at low phase angles and as bright features when the rings are viewed at high phase angles or the dark side of the rings is observed. However, we also find examples of spokes on the dark side of the rings that transition between being brighter and darker than the background ring as they move around the planet. Most interestingly, we also identify spokes that appear to be darker than the background ring near their center and brighter than the background ring near their edges. These “mixed spokes” indicate that the particle size distribution can vary spatially within a spoke. In addition, we document seasonal variations in the overall spoke activity over the course of the Cassini mission using statistics derived from lit-side imaging sequences. These statistics demonstrate that while spokes can be detected over a wide range of solar elevation angles, spoke activity increases dramatically when the Sun is within 10° of the ring plane.

A team of Earth-based astronomical observers supporting a giant planet entry-probe event substantially enhances the scientific return of the mission. An observers’ team provides spatial and temporal context, additional spectral coverage and resolution, viewing geometries that are not available from the probe or the main spacecraft, tracking, supporting data in case of a failure, calibration benchmarks, and additional opportunities for education and outreach. The capabilities of the support program can be extended by utilizing archived data. The existence of a standing group of observers facilitates the path towards acquiring Director’s Discretionary Time at major telescopes, if, for example, the probe’s entry date moves. The benefits of a team convened for a probe release provides enhanced scientific return throughout the mission. Finally, the types of observations and the organization of the teams described in this paper could serve as a model for flight projects in general. [ABSTRACT FROM AUTHOR]

This study investigates the propagation characteristics of Saturn's Narrowband (NB) emissions using a 3D ray‐tracing code incorporating Saturn's magnetic field and electron density parameters. The potential source regions and propagation zones of the L‐O mode, Z mode and whistler mode NB emissions are distinguished. The L‐O mode NB emissions, generated along local electron plasma frequency surfaces through mode conversion, exhibit straight‐line propagation but undergo reflections between the ionosphere, the plasma torus, and the magnetosheath. The slot region, characterized by a lower electron density distributed around the plasma torus boundary, significantly influences emission propagation, potentially leading to trapping and depolarization. The 5 kHz Z mode NB emissions propagate and fill the trapping region delineated by lower cut‐off and upper hybrid resonance frequencies. In contrast, the 20 kHz Z mode NB emissions are primarily confined near source regions at the north and south edges of the plasma torus, with the possibility of escaping under variable plasma conditions. Plain Language Summary: Scientists have discovered low‐frequency radio waves near Saturn, roughly at 5 and 20 kHz, using data from the Voyager and Cassini spacecrafts. These waves are referred to as narrowband (NB) emissions. The NB emissions are thought to originate from Saturn, but exhibit a puzzling propagation pattern when they propagate far away from their source region. Recent studies propose that the 5 kHz waves might be bouncing off a dense plasma area in Saturn's magnetosheath, introducing intriguing yet not fully understood propagation characteristics. This study employs a numerical approach, that is, the ray‐tracing technique, to trace the likely paths of these waves. Drawing on earlier theoretical studies, we pinpoint the potential origins of these waves. Our results indicate that most of these waves, particularly the so‐called L‐O mode emissions, tend to travel toward Saturn's high latitudes. This directional preference is due to interference from a dense plasma torus in Saturn's equatorial region. The boundary of this torus can trap these waves. Meanwhile, the so‐called Z mode waves are confined to a specific region near Saturn. Our study unveils intricate features such as multiple reflections and refractions of these waves near Saturn, shedding light on various data observations. Key Points: A 3D ray‐tracing analysis is conducted for Saturn Narrowband (NB) emissionsThe L‐O mode NB emissions propagate toward high latitudes and the Z mode NB emissions are trapped near SaturnSmall electron density structures on the plasma torus can lead to trapping and depolarization of NB emissions [ABSTRACT FROM AUTHOR]

Plasmaspheric hiss waves at the Earth are well known for causing losses of electrons from the radiation belts through wave particle interactions. At Saturn, however, we show that the different plasma density environment leads to acceleration of the electrons rather than loss. The ratio of plasma frequency to electron gyrofrequency frequently falls below one creating conditions for hiss to accelerate electrons. The location of hiss at high latitudes (>25°) coincides very well with this region of very low density. The interaction between electrons and hiss only occurs at these higher latitudes, therefore the acceleration is limited to mid to low pitch angles leading to butterfly pitch angle distributions. The hiss is typically an order of magnitude stronger than chorus at Saturn and the resulting acceleration is rapid, approaching steady state in one day at 0.4 MeV at L = 7 and the effect is stronger with increasing L-shell.

Abstract New interior models of Jupiter and Saturn suggest that both planets have “fuzzy cores.” These cores should be viewed as central regions that are enriched with heavy elements but are not distinct from the rest of the deep interior. These cores may contain large amounts of hydrogen and helium though small pure heavy‐element cores may also exist. New measurements along with advanced planetary modeling have revolutionized the way we think about the interiors of giant planets and provide important constraints for planet formation and evolution theories. These developments are also relevant for the characterization of giant exoplanets.

Jupiter's equatorial eastward zonal flows reach wind velocities of ∼100 m s−1, while on Saturn they are three times as strong and extend about twice as wide in latitude, despite the two planets being overall dynamically similar. Recent gravity measurements obtained by the Juno and Cassini spacecraft uncovered that the depth of zonal flows on Saturn is about three times greater than on Jupiter. Here we show, using 3D deep convection simulations, that the atmospheric depth is the determining factor controlling both the strength and latitudinal extent of the equatorial zonal flows, consistent with the measurements for both planets. We show that the atmospheric depth is proportional to the convectively driven eddy momentum flux, which controls the strength of the zonal flows. These results provide a mechanistic explanation for the observed differences in the equatorial regions of Jupiter and Saturn, and offer new understandings about the dynamics of gas giants beyond the Solar System. Plain Language Summary: In this study, we investigate the strong eastward jet around the equator of Jupiter and Saturn. Despite the planets being similar, Saturn's winds are stronger and cover a wider area in latitude. Recent spacecraft measurements revealed that Saturn's winds go much deeper into its interior than Jupiter's. Using numerical simulations, we find that the depth of the atmosphere is crucial in determining the strength and width of these winds. We show that the depth is related to a specific turbulent flow, dictating the strength of the jets. These findings explain why Jupiter and Saturn have different equatorial zonal wind patterns and provide new insights into the behavior of giant planets outside the Solar System. Key Points: Through 3D numerical simulations, we deduce that the flow depth of gas giants significantly influences their equatorial dynamicsEquatorial flows are driven by eddy fluxes perpendicular to the axis of rotation, and these fluxes are proportionate to the flow depthThe zonal flow depth of Jupiter and Saturn, inversely proportional to their 3:1 mass ratio, leads to the corresponding ratio in flow strength [ABSTRACT FROM AUTHOR]

Tidal interactions between moons and planets can have major effects on the orbits, spins, and thermal evolution of the moons. In the Saturn system, tidal dissipation in the planet transfers angular momentum from Saturn to the moons, causing them to migrate outwards. The rate of migration is determined by the mechanism of dissipation within the planet, which is closely tied to the planet's uncertain structure. We review current knowledge of giant planet internal structure and evolution, which has improved thanks to data from the Juno and Cassini missions. We discuss general principles of tidal dissipation, describing both equilibrium and dynamical tides, and how dissipation can occur in a solid core or a fluid envelope. Finally, we discuss the possibility of resonance locking, whereby a moon can lock into resonance with a planetary oscillation mode, producing enhanced tidal migration relative to classical theories, and possibly explaining recent measurements of moon migration rates. [ABSTRACT FROM AUTHOR]

A theory about a young, evolving "stealth ocean" under the ancient-looking surface of Mimas, the moon of Saturn, triggered us to revisit the icy satellite and develop a revised geological map based on Cassini images. The re-mapping of Mimas's surface aimed to fill the decades-long gap that grew since the publication of the first Voyager image-based pioneering map, and it provided an up-to-date synthetic interpretation of revised and newly discovered features. Despite the map being in its early stage of introduction, it already showed some key features that may play significant roles in the reconstruction of Mimas's (surface) evolution. The Herschel crater, formed by a global-scale impact, undoubtedly left additional marks, including fault scarps, stair-step faults, and post-impact surface transformation, through mass movements around the crater wall and the peak. Smaller craters left various scars on the surface, including asymmetric craters, whose morphology and allocation we used to reconstruct the regional topographic changes on the surface of Mimas. In addition to the impact-related features, which dominated the surface of the icy satellite, groups of weak, quasi-parallel running linear features, such as undifferentiated lineaments, grooves/through, and ridges, were also observed. The appearance and pattern of those lineaments overlapped with the allocation of various modeled global nonlinear tidal dissipations, supporting the existence of theoretical subsurface stealth oceans. [ABSTRACT FROM AUTHOR]

Until recently, observations of the giant planets of our Solar System were confined to sampling relatively shallow regions of their atmospheres, leaving many uncertainties as to the dynamics of deeper layers. The Cassini and Juno missions to Saturn and Jupiter, however, have begun to address these issues, for example, by measuring their gravity and magnetic fields. The results show that the zonally coherent jets and cloud bands extend to levels where the electrical conductivity of the fluid becomes significant, whereas large-scale vortices, such as the Great Red Spot, are relatively shallow but may have deep-seated roots. The polar regions also exhibit intense cyclonic vortices that, on Jupiter, arrange themselves into remarkably regular "vortex crystals." Numerical models seem able to capture some of this complexity, but many issues remain unresolved, suggesting a need for models that can represent both deep and shallow processes sufficiently realistic ally to compare with observations. [ABSTRACT FROM AUTHOR]

The Saturnian system has been explored by four spacecraft: Pioneer 11, Voyager 1 and 2, and Cassini. Only the last three took images suitable for photogeologic analysis of the surfaces of Saturn's moons, and over the decades, several research groups have published data about the crater distributions on the Saturnian satellites. These groups have used those data to draw conclusions about the impactor populations and resurfacing histories of the moons, but no one has examined how well the different data agree between the researchers. We present independent mapping of the crater populations of Saturn's moons Mimas, Rhea, and Iapetus, and compare them with many published crater populations. We found that Mimas data are the most consistent between different researchers, and Rhea data are the least consistent. We attribute these differences to (a) data biases where there are fewer images upon which to map Mimantean craters but a large variety exist for Rhean, and (b) Rhea likely has different terrains with different impact crater populations which have not been generally recognized before. We also found that Iapetus' small craters appear to have a shallow branch, as others have found, and that shallow branch is not attributable to completeness limitations. Other bodies have shallow branches at small diameters, too, but they are not as shallow as Iapetus's, which suggests varying impacting populations as one moves closer to Saturn, in line with others' work on planetocentric impactors. Plain Language Summary: Saturn has 146 known moons. The largest, Titan, has a thick atmosphere and few impact craters on its surface. The six next‐largest moons are Rhea, Iapetus, Tethys, Dione, Enceladus, and Mimas. In this work, we studied craters on Rhea, Iapetus, and Mimas to better understand crater populations on their surfaces, how craters vary from moon to moon, how craters vary based on researcher differences, and what craters can tell us about objects in the outer solar system that made them. After cataloging more than 150,000 craters, we found that different researchers disagree most about craters on Rhea's surface, which suggests there might be some significant differences from location to location on Rhea. We found that smaller craters on Iapetus are the fewest in number relative to large craters of the three moons we studied. Since Iapetus is farthest from Saturn, we interpret this to mean that they more closely resemble the population of bodies orbiting the Sun in the outer solar system hitting these moons. We found that the population from moon to moon appears to change at small sizes, which suggests that impactors encircling Saturn form distinct impacting populations, too. Key Points: We mapped 10,981, 45,817, and 103,054 impact craters across Saturn's moons Mimas, Iapetus, and Rhea, respectivelyWe compare the crater populations to those of other researchers, and we found the best agreement on Mimas and worst on RheaThe satellites are indistinguishable from cratering equilibrium at 10 s km and were impacted by a shallow population with small diameters [ABSTRACT FROM AUTHOR]

Enceladus, an icy moon of Saturn, is a compelling destination for a probe seeking biosignatures of extraterrestrial life because its subsurface ocean exhibits significant organic chemistry that is directly accessible by sampling cryovolcanic plumes. State-of-the-art organic chemical analysis instruments can perform valuable science measurements at Enceladus provided they receive sufficient plume material in a fly-by or orbiter plume transit. To explore the feasibility of plume sampling, we performed light gas gun experiments impacting micrometer-sized ice particles containing a fluorescent dye biosignature simulant into a variety of soft metal capture surfaces at velocities from 800 m ⋅ s-1 up to 3 km ⋅ s-1 Quantitative fluorescence microscopy of the capture surfaces demonstrates organic capture efficiencies of up to 80 to 90% for isolated impact craters and of at least 17% on average on indium and aluminum capture surfaces at velocities up to 2.2 km ⋅ s-1 Our results reveal the relationships between impact velocity, particle size, capture surface, and capture efficiency for a variety of possible plume transit scenarios. Combined with sensitive microfluidic chemical analysis instruments, we predict that our capture system can be used to detect organic molecules in Enceladus plume ice at the 1 nM level-a sensitivity thought to be meaningful and informative for probing habitability and biosignatures.

Supernova (SN) blasts envelop many surrounding stellar systems, transferring kinetic energy to small bodies in the systems. Geologic evidence from ^60 Fe points to recent nearby SN activity within the past several Myr. Here, we model the transfer of energy and resulting orbital changes from these SN blasts to the Oort Cloud, the Kuiper Belt, and Saturn’s Phoebe ring. For the Oort Cloud, an impulse approximation shows that a 50 pc SN can eject approximately half of all objects less than 1 cm while altering the trajectories of larger ones, depending on their orbital parameters. For stars closest to SNe, objects up to ∼100 m can be ejected. Turning to the explored solar system, we find that SNe closer than 50 pc may affect Saturn’s Phoebe ring and can sweep away Kuiper Belt dust. It is also possible that the passage of the solar system through a dense interstellar cloud could have a similar effect; a numerical trajectory simulation shows that the location of the dust grains and the direction of the wind (from an SN or interstellar cloud) has a significant impact on whether or not the grains will become unbound from their orbit in the Kuiper Belt. Overall, nearby SNe sweep micron-sized dust from the solar system, though whether the grains are ultimately cast toward the Sun or altogether ejected depends on various factors. Evidence of SN-modified dust grain trajectories may be observed by New Horizons, though further modeling efforts are required.

Recent observational constraints on the internal structure of Jupiter and Saturn suggest that these planets have “fuzzy” cores, i.e., gradients of the concentration of heavy elements that might span a large fraction of the planet’s radius. These cores could be composed of a semiconvective staircase, i.e., multiple convective layers separated by diffusive interfaces arising from double-diffusive instabilities. However, to date, no study has demonstrated how such staircases can avoid layer mergers and persist over evolutionary timescales. In fact, previous work has found that these mergers occur rapidly, leading to only a single convective layer. Using 3D simulations, we demonstrate that rotation prolongs the lifetime of a convective staircase by increasing the timescale for both layer merger and erosion of the interface between the final two layers. We present an analytic model for the erosion phase, predicting that rotation increases the erosion time by a factor of approximately Ro ^−1/2 , where Ro is the Rossby number of the convective flows (the ratio of the rotation period to the convective turnover time). For Jovian conditions at early times after formation (when convection is vigorous enough to mix a large fraction of the planet), we find the erosion time to be roughly 10 ^9 yr in the nonrotating case and 10 ^11 yr in the rotating case. If these timescales are confirmed with a larger suite of numerical simulations, the existence of convective staircases within the deep interiors of giant planets is a strong possibility, and rotation could be an important factor in the preservation of their fuzzy cores.

A review of studies on the atmospheres of planets in the solar system performed by Russian scientists in 2019–2022 is presented. This review was prepared in the Commission on Planetary Atmospheres of the National Geophysical Committee for the National Report on Meteorology and Atmospheric Science at the 28th General Assembly of the International Union of Geodesy and Geophysics (IUGG 2023) in Berlin. [ABSTRACT FROM AUTHOR]

The Wispy Terrain is the region of chasmata characterized by quasi-parallel fault systems, formed by extensional and shear stresses of the icy crust of Dione, a moon of Saturn. Besides the basic, satellite-scale geological mapping and very general definition of the phenomenon, only a few studies focus on the Wispy Terrain and its chasmata from the angle of detailed tectonic reconstruction, with others mainly targeting, e.g., the timing of its formation. This study provides a detailed geological and cryotectonic analysis in the surroundings of the Eurotas and Palatine Chasmata and proposes additional, until now, unidentified tectonic processes and a formation model. The relationship between fragmentary impact craters and tectonic features indicates other newly suspected tectonic movements, namely thrust, and splay and décollement fault systems. In contrast to the commonly expected and identified dilatational processes, such fault types show compression and are characteristic of subduction in a terrestrial environment. Theoretically, the appearance of such tectonic processes means that the already-known rift and the newly discovered subsumption (subduction-like) processes may appear together in the Wispy Terrain. The appearance of both features may suggest the presence of some of the components (phases) of a Wilson cycle analog cryotectonic cycle (or possibly cycles) in icy planetary bodies like Dione. [ABSTRACT FROM AUTHOR]

Saturn Kilometric Radiation (SKR) is a non‐thermal auroral emission with peak emission occurring at 100–400 kHz. Its properties have been extensively studied since Cassini's arrival at Saturn until mission end with its Radio and Plasma Wave Science (RPWS) experiment. Low Frequency Extensions (LFEs) of SKR which consist of global intensifications of SKR accompanied by extensions of the main SKR band down to lower frequencies have been studied in particular. Low Frequency Extensions result from internally driven tail reconnection and from solar wind compressions of the magnetosphere, which also trigger tail reconnection. They have been cataloged through visual inspection with two approaches, using an intensity threshold for LFEs in 2006 (Reed et al., 2018, https://doi.org/10.1002/2017ja024499) and more recently O'Dwyer et al. (2023a, https://doi.org/10.25546/103103) produced a sample of LFEs detected by Cassini/RPWS by fitting their exact frequency‐time coordinates with polygons. In this study we use the latter catalog of LFEs as a training set for an image based machine learning algorithm to classify all LFEs detected by Cassini/RPWS. The inputs to the model are multi‐channel images consisting of spectrogram images in flux density and degree of circular polarization. The outputs of the model are binary masks showing the exact location of the LFE in frequency‐time space. The median Intersection Over Union across the testing and training set were calculated to be 0.97 and 0.98, respectively. The output of this study is a list of all 4,874 LFEs detected using this method. The list of LFE frequency‐time coordinates is available for use amongst the scientific community. Plain Language Summary: We are using radio observations from the Cassini spacecraft that was in orbit around the planet Saturn for 13 years. We want to search for characteristic features of Saturn's auroral radio emissions (called Saturn Kilometric Radiation or SKR) in the data stream from the radio instrument—specifically events called Low Frequency Extensions (LFEs). The edges of these events can be tracked in time‐frequency spectrograms of Cassini radio observations. We find several hundred examples of the LFEs that we're looking for, and feed these into a computer algorithm which learns what they look like. The algorithm can then be applied to new/unseen data and we allow it to search for similar events. The end result is an extensive catalog of all the LFEs observed throughout the 13‐year near‐Saturn mission by the radio instrument of Cassini. This catalog can be used by the scientific community as a basis for statistical studies of Saturn's radio emissions. The machine learning aspect of this work can be adapted through something known as transfer learning to other planets where we look for similar features in data. Key Points: Supervised learning applied to database of labeled polygons marked on radio spectrogramsFocus on Low Frequency Extensions of Saturn Kilometric Radiation to return a full catalog from the Cassini missionA modified U‐Net architecture achieved median Intersection over Union values of 0.98 and 0.97 across the training and testing set [ABSTRACT FROM AUTHOR]

The rich culture of old Maya gave birth to a very complicated and complex calendar; they also recorded important historical events and many significant astronomical phenomena. The main source of information is represented by Dresden Codex (DC), one of the four preserved Mayan hieroglyphic literal legacies. DC roughly covers the interval between 280 and 1325 AD. The old problem of precise Mayan dating with respect to our calendar is traditionally called correlation; it expresses the difference in days between the Long Count of the Mayan calendar and the Julian Date, used in presentday astronomy. There exist more than fifty published correlations that differ one from the other by as much as several centuries. Historians mostly accept the so called Goodman-Martínez-Thompson (GMT) value of 584 283 days, which is based mostly on historical events extracted from the sources of a postclassical period of Mayan history. On the contrary, brothers Böhm used precisely dated astronomical data from classical period to derive the Böhm correlation (BB) of 622 261 days. Unlike the GMT correlation it is in excellent agreement with the astronomical phenomena recorded in DC. Since then we published several papers supporting the validity of BB correlation and its advantage over GMT in the classical period of Mayan history. To this end, we used more records of astronomical phenomena discovered in DC. This study describes six records of planetary conjunctions that we found recently on p. 37 of DC that concern planets Mercury, Venus, Mars, Jupiter, and Saturn. All of these records coincide with the real occurrences of these phenomena within several days, if BB correlation is applied.

Saturn's northern summertime hemisphere was mapped by JWST/Mid‐Infrared Instrument (4.9–27.9 µm) in November 2022, tracing the seasonal evolution of temperatures, aerosols, and chemical species in the 5 years since the end of the Cassini mission. The spectral region between reflected sunlight and thermal emission (5.1–6.8 µm) is mapped for the first time, enabling retrievals of phosphine, ammonia, and water, alongside a system of two aerosol layers (an upper tropospheric haze p < 0.3 bars, and a deeper cloud layer at 1–2 bars). Ammonia displays substantial equatorial enrichment, suggesting similar dynamical processes to those found in Jupiter's equatorial zone. Saturn's North Polar Stratospheric Vortex has warmed since 2017, entrained by westward winds at p < 10 mbar, and exhibits localized enhancements in several hydrocarbons. The strongest latitudinal temperature gradients are co‐located with the peaks of the zonal winds, implying wind decay with altitude. Reflectivity contrasts at 5–6 µm compare favorably with albedo contrasts observed by Hubble, and several discrete vortices are observed. A warm equatorial stratospheric band in 2022 is not consistent with a 15‐year repeatability for the equatorial oscillation. A stacked system of windshear zones dominates Saturn's equatorial stratosphere, and implies a westward equatorial jet near 1–5 mbar at this epoch. Lower stratospheric temperatures, and local minima in the distributions of several hydrocarbons, imply low‐latitude upwelling and a reversal of Saturn's interhemispheric circulation since equinox. Latitudinal distributions of stratospheric ethylene, benzene, methyl, and carbon dioxide are presented for the first time, and we report the first detection of propane bands in the 8–11 µm region. Plain Language Summary: The Saturn system, with its seasonally varying atmosphere, delicate rings, and myriad satellites, presented an ideal early target for JWST. Saturn's extended disc, rapid rotation, and infrared brightness provided a challenge for the small fields‐of‐view of the Mid‐Infrared Instrument (MIRI), requiring a mosaic to map Saturn's northern summertime hemisphere. This exquisite data set reveals Saturn's banded structure, discrete vortices, the warm polar vortices, and the continued evolution of an oscillatory pattern of warm and cool anomalies over Saturn's equator. We show evidence that a stratospheric circulation pattern detected by Cassini during northern winter has now fully reversed in northern summer, with the low‐latitude stratosphere being cool and depleted in aerosols due to summertime upwelling. MIRI provides access to spectral regions that were not possible with the Cassini spacecraft, particularly in the 5–7 μm region where reflected sunlight and thermal emission blend together. Ammonia and phosphine are enriched at Saturn's equator, suggesting strong mixing from the deeper troposphere. MIRI's high sensitivity enables the first identification of previously unseen emission propane bands, along with the first measurements of the distribution of several gaseous species: tropospheric water, and stratospheric ethylene, benzene, methyl, and carbon dioxide. Key Points: Saturn's northern summertime hemisphere was mapped by JWST/Mid‐Infrared Instrument (MIRI) to study seasonal evolution of temperatures, aerosols, and compositionThe data show evidence for changing temperatures and winds in the equatorial oscillation, polar vortices, and interhemispheric stratospheric circulationMIRI spectral coverage and sensitivity enables mapping of several gases for the first time, particularly in ranges inaccessible to Cassini [ABSTRACT FROM AUTHOR]

Foam aluminum is a promising material with a unique combination of mechanical and operational properties: low specific gravity, low thermal conductivity, the ability to absorb acoustic and electromagnetic oscillations, and the ability to deform under constant load. At present, the most used methods for producing aluminum foam are methods based on mixing a gas or blowing agent (porophore) into the aluminum melt and forming a porous structure during the aluminum melt solidification. An alternative to this technology is the formation of a porous structure through the use of soluble granules, which are pre-filled in the mold, and then, after the granules are impregnated with aluminum melt and the casting is solidified, they are leached. Studies of porous aluminum formation processes carried out by impregnation of a mold with soluble granules with an aluminum melt confirmed that the melt cooling rate depends on the thermal casting conditions (the mold temperature with granules and the poured alloy temperature), as well as on the size of water-soluble granules, their thermophysical properties and their packing density in the mold. Calculation and experimental studies have shown that the melt cooling rate in a mold with water-soluble granules is 1.8–10 times higher than when casting off solid aluminum castings. Porous aluminum structure metallographic studies have shown that the grain size is 2–4 times smaller than that of solid castings. [ABSTRACT FROM AUTHOR]

Electron acceleration at Saturn due to whistler mode chorus waves has previously been assumed to be ineffective; new data closer to the planet show it can be very rapid (factor of 104 flux increase at 1 MeV in 10 days compared to factor of 2). A full survey of chorus waves at Saturn is combined with an improved plasma density model to show that where the plasma frequency falls below the gyrofrequency additional strong resonances are observed favoring electron acceleration. This results in strong chorus acceleration between approximately 2.5 R S and 5.5 R S outside which adiabatic transport may dominate. Strong pitch angle dependence results in butterfly pitch angle distributions that flatten over a few days at 100s keV, tens of days at MeV energies which may explain observations of butterfly distributions of MeV electrons near L=3. Including cross terms in the simulations increases the tendency toward butterfly distributions.