Search

During its more than 13 years in orbit, the Cassini spacecraft detected a large number of plasma and energetic charged particle injections in Saturn's inner magnetosphere. In the corotating frame of the planet, the plasma contained within an injection moves radially inward with the component particles gaining energy. The highest energy particles in the injection experience stronger gradient-curvature drifts in the longitudinal direction and can drift out of the main body of the injection. We have used these drift-out effects to estimate the inflow speed of 19 injections by surveying cases from the available plasma data. We find that the average inflow speed from our sample is 22 km/s, and the values are well distributed between 0 and 50 km/s, with a few higher estimates. We have also computed the radial travel distance of interchange events and found that these are typically one to two Saturn radii. We discuss the implications of these quantifications on our understanding of transport. [ABSTRACT FROM AUTHOR]

This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE‐I) sensor on Juno from 10–40 RJ in the dawn to midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5–22, and the observations are separated by equatorial (|zmag[RJ]| ≤ 1.5) and off‐equator (|zmag[RJ]|>1.5) regions. Plasma parameters for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ are derived by forward modeling JADE‐I's energy‐per‐charge versus time‐of‐flight spectra using omnidirectional averaged convected kappa distributions and modeled instrument responses. O+ and S2+ are resolved via a ray‐tracing simulation based on carbon‐foil‐effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to ∼20 RJ. Ion number densities decrease with radial distance, the primary species being H+, O+, and S2+. The relative contribution of H+ and S2+ increases and decreases, respectively, in the off‐equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O+ to S2+ and ΣOn+ to ΣSn+ number density ratios are variable, the 5 RJ bin averages for O+ to S2+ ranging from ∼0.75–1.5 (equator) and ∼1.1–1.8 (off‐equator) and ΣOn+ to ΣSn+ from ∼0.6–0.9 (equator) and ∼0.8–1.1 (off‐equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 RJ and range from ∼100 eV to 10 keV and 1 keV to a few tens of keV, respectively. Plain Language Summary: The Jovian Auroral Distributions Experiment (JADE) on Juno has continuously investigated the plasma environment in Jupiter's magnetosphere since its arrival in August 2016. The polar‐orbiting spacecraft enables JADE to explore both equatorial and off‐equator regions of Jupiter's plasma sheet. In this study, we present plasma sheet ion characteristics such as ion composition, flow speed, and temperatures for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ that are originating from the innermost Galilean satellite Io. A spatial dependence of ion characteristics is discussed and compared to previous observations. While the density profiles agree well with the Voyager‐based studies, temperatures found in this study show at least an order of magnitude higher values. A new addition to this paper is that the latitudinal distribution of ions shows trend in the mass. Relative composition of protons increases compared to the heavier ions in the off‐equator regions. These observations provide insights on how the ions are distributed throughout Jupiter's magnetosphere and improve our current understanding on ion dynamics in the plasma sheet. Key Points: Ion flow speed, number density, temperature, and composition in Jupiter's plasma sheet show radial and/or latitudinal trendsH+, O+, and S2+ are the primary ions, the contribution of H+ and S2+ increasing and decreasing, respectively, in the off‐equator regionThe O+ to S2+ density ratio is variable, the 5 RJ bin averages ranging from 0.7–1.5 (equator) and 1.1–1.8 (off‐equator) [ABSTRACT FROM AUTHOR]

Jupiter's auroral X‐rays have been observed for 40 years with an unknown driver producing quasiperiodic emission, concentrated into auroral hot spots. In this study we analyze an ∼ 10‐hr Chandra observation from 18:56 on 18 June 2017. We use a new Python pipeline to analyze the auroral morphology, perform timing analysis by incorporating Rayleigh testing, and use in situ Juno observations to infer the magnetosphere that was compressed during the Chandra interval. During this time Juno was near its apojove position of ∼112 RJ, on the dawn flank of the magnetosphere near the nominal magnetopause position. We present new dynamical polar plots showing an extended X‐ray hot spot in the northern auroral region traversing across the Jovian disk. From this morphology, we propose setting a numerical threshold of >7 photons per 5° System III longitude × 5° latitude to define a photon concentration of the northern hot spot region. Our timing analysis finds two significant quasiperiodic oscillations (QPOs) of ∼37 and ∼26 min within the extended northern hot spot. No statistically significant QPOs were found in the southern X‐ray auroral emission. The Rayleigh test is combined with Monte Carlo simulation to find the statistical significance of any QPOs found. We use a flux equivalence mapping model to trace the possible origin of the QPOs, and thus the driver, to the dayside magnetopause boundary. Key Points: Analysis is performed on a Chandra campaign observing Jupiter's X‐ray emissions during the apojove portion of Juno's orbit on 18 June 2017We use Juno magnetopause crossings to infer a compressed magnetosphere during the X‐ray campaignQuasiperiodic pulsing of the northern X-ray hot spot are mapped to a location close to the dayside magnetopause [ABSTRACT FROM AUTHOR]

The Jovian Auroral Distributions Experiment Ion sensor (JADE‐I) on Juno is a plasma instrument that measures the energy‐per‐charge (E/Q) distribution of 0.01 to 46.2 keV/q ions over a mass‐per‐charge (M/Q) range of 1– 64 amu/q. However, distinguishing O+ and S2+ from JADE‐I's measurements is a challenging task due to similarities in their M/Q (∼16 amu/q). Because of this, O+ and S2+ have not been fully resolved in the in situ measurements made by plasma instruments at Jupiter (e.g., Voyager PLS and Galileo PLS) and their relative ratios has been studied using physical chemistry models and ultraviolet remote observations. To resolve this ambiguity, a ray tracing simulation combined with carbon foil effects is developed and used to obtain instrument response functions for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+. The simulation results indicate that JADE‐I can resolve the M/Q ambiguity between O+ and S2+ due to a significant difference in their charge state modification process and a presence of a large electric potential difference (∼8 kV) between its carbon foils and MCPs. A forward model based on instrument response functions and convected kappa distributions is then used to obtain ion properties at the equatorial plasma sheet (∼36 RJ) in the predawn sector of magnetosphere. The number density ratio between O+ and S2+ for the selected plasma sheet crossings ranges from 0.2 to 0.7 (0.37 ± 0.12) and the number density ratio between total oxygen ions to total sulfur ions ranges from 0.2 to 0.6 (0.41 ± 0.09). Key Points: A technique to resolve mass‐per‐charge ambiguity of O+ and S2+ for ESA‐TOF instruments using carbon foil effectsAn analysis tool to extract ion distributions from in situ measurements of Juno JADE‐IIon bulk properties derived from the forward model with convected kappa distributions in the jovian plasma sheet [ABSTRACT FROM AUTHOR]

Measurement of O+ in the Earth's magnetosphere is important for monitoring and understanding the initiation and evolution of geomagnetic activity. During active times, O+ can be the most abundant ion in the magnetosphere. Furthermore, because O+ and H+ damage exposed spacecraft materials through different processes, measurement and prediction of O+ and H+ fluxes is critical for understanding cumulative damage effects to these materials resulting from the ambient plasma environment of a spacecraft. We describe a simple technique for quantitative, in situ measurement of O+ and H+ fluxes using ultrathin foils. This technique is a low‐resource addition to a standard electrostatic energy‐per‐charge analyzer followed by an array of detectors. H+ and O+ abundances up to a few tens of keV can be determined by comparison of counts in detectors having no ultrathin foil at the detector aperture, in which both H+ and O+ are detected, and adjacent detectors having a foil over the aperture of the appropriate thickness to stop the transmission of O+ but through which H+ can transit. We describe three techniques for implementing this method enabling differentiation of O+ and H+ in an instrument package significantly simpler than traditional mass spectrometers. Plain Language Summary: Measurement of oxygen ions in near‐Earth space is important for monitoring and understanding the current state of the magnetosphere. While hydrogen is typically the most abundant ion in the magnetosphere, during times of enhanced geomagnetic activity oxygen can dominate. Additionally, oxygen and hydrogen ions can damage exposed spacecraft materials by species‐dependent processes. Thus, measurement and prediction of oxygen and hydrogen fluxes is critical for understanding cumulative damage effects to spacecraft materials as well as determining magnetospheric activity levels. We describe a simple, low‐resource technique for measuring oxygen and hydrogen fluxes in the spacecraft's local plasma environment. This concept utilizes standard measurement techniques for energy selection followed by an array of detectors. The concept uses two types of detectors: one covered with an ultrathin foil and one with no foil. The detector with the foil will measure hydrogen only, as the foil is specifically tuned to prevent oxygen transmission. The detector with no foil measures both oxygen and hydrogen. The abundances of oxygen and hydrogen can be determined by comparison of counts in the two detector types. We describe three techniques for implementing this method enabling differentiation of oxygen and hydrogen in an instrument package significantly simpler than traditional mass spectrometers. Key Points: Measurement of magnetospheric H+ and O+ is critical for understanding dynamics and energization processesA novel application of ultrathin foils enables low‐resource detection of magnetospheric H+ and O+Three implementation schemes of this low‐resource measurement technique are presented, with one scheme already successfully on‐orbit [ABSTRACT FROM AUTHOR]

The Cassini spacecraft orbited the planet Saturn from July 2004 to September 2017, and its varied orbital trajectory took it across the magnetopause and bow shock boundaries multiple times, at varying radial distances, local times, latitudes, and phases of the solar cycle. Here we present a comprehensive list of these boundary crossings, derived primarily using data from the Cassini magnetometer instrument, with cross‐validation against the electron spectrometer data where available. There are a multitude of scientific avenues for exploitation of this list. In this work, we examine the variability in boundary location and use the crossing times in concert with models of the bow shock and magnetopause to infer the upstream solar wind dynamic pressure at the times of crossings. This analysis allows us to understand the limitations of the Cassini trajectory for studying boundary physics under a range of solar wind driving conditions. In addition, rapid traversals of the magnetosheath are used to estimate the range of speeds of boundary motion. Key Points: Comprehensive set of magnetopause and bow shock crossings spanning the entire Cassini mission presentedCrossings used in conjunction with boundary models to infer upstream solar wind dynamic pressure and range of standoff distancesRapid traversals of magnetosheath explored in context of rapidly changing external conditions [ABSTRACT FROM AUTHOR]

An analytical method is developed by which measurements made by the Cassini spacecraft in Saturn's magnetosheath can be used to infer the upstream solar wind parameters, specifically the solar wind speed (Vsw) and the dynamic pressure (Pd). The method is validated by comparing the results with other estimates of these parameters, including the mSWiM MHD model and magnetopause and bow shock models applied to observed boundary crossings. The comparisons suggest that the new inferred Vsw are on average ~40 km/s lower than the mSWiM values, and the dynamic pressure values are slightly lower as well. We find few of the lower Pd values predicted by mSWiM, probably because Cassini would have been inside the expanded magnetosphere under such conditions. Systematic temporal variations such as interplanetary shocks do seem to be captured well, with arrival times within several days of the MHD prediction. Compared to dynamic pressures estimated from boundary crossings with well‐known magnetopause and bow shock models, the magnetosheath‐inferred dynamic pressure tends to be somewhat lower, but within the uncertainties of the analytical derivation. Comparison of the inferred dynamic pressure with observed Saturn's kilometric radiation (SKR) activity reveals several episodes of very good temporal tracking between dynamic pressure and SKR intensity, with relatively short time delays (4–5 hr), suggesting rather direct driving. Such good tracking intervals occur almost exclusively on the dawnside of the magnetosphere, where the dominant SKR source is visible. When the tracking is good, the SKR fluxes vary roughly as the square of the dynamic pressure. Plain Language Summary: The extent to which Saturn's magnetosphere may be driven by variations in the upstream solar wind is not well understood, in part because single‐spacecraft missions provide no monitor of the upstream plasma to accompany the in situ magnetospheric measurements. One global measure of magnetospheric activity is Saturn's kilometric radiation (SKR). Remote observations of SKR can be combined with solar wind measurements to explore the solar wind's influence on the magnetosphere. We propose a method for greatly increasing the amount of time for which the upstream conditions can be known by using the large database of measurements made by Cassini when it was in Saturn's magnetosheath, the shocked solar wind that coats the sunward side of the magnetosphere. The resulting parameters are validated by comparison with other estimates. Then comparison with Cassini SKR observations reveals that at some times the SKR fluxes clearly track the variations in the solar wind dynamic pressure, suggesting a rather direct solar wind driving of at least some of the magnetospheric processes that produce SKR. Key Points: Analytical development of method to estimate upstream solar wind parameters from Cassini measurements in Saturn's magnetosheathResults in generally good agreement with solar wind speed and dynamic pressure estimated by other meansSome several‐day intervals are found where there is good tracking between the inferred dynamic pressure and SKR intensities [ABSTRACT FROM AUTHOR]

The low‐altitude, high‐velocity trajectory of the Juno spacecraft enables the Jovian Auroral Distributions Experiment to make the first in situ observations of the high‐latitude ionospheric plasma. Ions are observed to energies below 1 eV. The high‐latitude ionospheric ions are observed simultaneously with a loss cone in the magnetospheric ions, suggesting precipitating magnetospheric ions contribute to the heating of the upper ionosphere, raising the scale height, and pushing ionospheric ions to altitudes of 0.5 RJ above the planet where they are observed by Jovian Auroral Distributions Experiment. The source of the magnetospheric ions is tied to the Io torus and plasma sheet, indicated by the cutoff seen in both the magnetospheric and ionospheric plasma at the Io M‐shells. Equatorward of the Io M‐shell boundary, the ionospheric ions are not observed, indicating a drop in the scale height of the ionospheric ions at those latitudes. Plain Language Summary: The Jovian Auroral Distributions Experiment (JADE) ion sensor has made the first in situ observations of the upper, high‐latitude ionosphere of Jupiter. Flown on the Juno spacecraft, JADE observes the ionosphere at altitudes of approximately half a Jovian radii, with the spacecraft traveling at the high speed of ~50 km/s. For comparison, a proton traveling at 50 km/s has an energy of approximately 10 eV. The combination of the low‐altitude and high ram velocity enables JADE to measure ionospheric ions to energies below 1 eV. These observations reveal a cold ionospheric population of protons at high latitudes, seen coincident with precipitating magnetospheric ions. This indicates that the precipitating magnetospheric ions heat the upper ionosphere, raising the height where these protons can be observed. The ionospheric protons are seen in bands in the northern and southern latitudes, bounded on the equator edge by the field lines that connect to Io, and inside the auroral oval to the poleward side. Key Points: The high‐latitude ionosphere is observed between the magnetic latitudes bounded by the auroral oval and Io's magnetic flux shellTwo populations are observed at high latitudes: (1) magnetospheric ions consisting of H, S, and O ions and (2) cold ionospheric H+ ionsObservation of a loss cone suggests precipitating magnetospheric ions heat the upper ionosphere to heights ~0.5 RJ above the clouds [ABSTRACT FROM AUTHOR]

Saturn's magnetosphere has been extensively studied over the past 13 years with the now retired Cassini mission. Periodic modulations in a variety of magnetospheric phenomena have been observed at periods close to those associated with the emission intensity of Saturn kilometric radiation (SKR). Resulting from Rayleigh‐Taylor like plasma instabilities, interchange is believed to be the main plasma transport process in Saturn's inner to middle magnetosphere. Here we examine the organization of equatorially observed interchange events identified based on high‐energy (3–22 keV) H+ intensifications by several longitude systems that have been derived from different types of measurements. The main question of interest here is as follows: Do interchange injections undergo periodicities similar to the Saturn kilometric radiation or other magnetospheric phenomena? We find that interchange shows enhanced occurrence rates in the northern longitude systems between 30° and 120°, particularly between 7 and 9 Saturn Radii. However, this modulation is small compared to the organization by local time. Additionally, this organization is weak and inconsistent with previous findings based on data with a limited time span. Plain Language Summary: When estimating the rotation rate of Jupiter and Saturn, scientists often use a periodic signal of radio emission from the planet's auroral region. At Saturn this emission is called the Saturn kilometric radiation (SKR), and unlike Jupiter, the period of SKR is observed to vary over time. Similar periodic variations have also been observed in particle energy and magnetic fields, suggesting that this periodicity is a fundamental property of the Saturn space environment. In this work, we ask if these same repetitions can be seen in a process called interchange injection. To do this, we analyze interchange's occurrence rate, as observed in particle data from the Cassini spacecraft, with respect to two longitude systems previously derived from the observed periods of the SKR emission. We find that interchange occurrence shows only weak organization in these longitude systems as compared to organization by local time. Key Points: Interchange injections, identified from an automated detection method, shows strongest organization in local time compared to longitudeLongitude system dependence of equatorial interchange injections exists, but it is weak and inconsistent to previous worksInterchange occurrence rates weakly peak at ~90° in northern SLS‐5 and PPO between 7 and 9 Saturn Radii but occur at all longitudes and seasons [ABSTRACT FROM AUTHOR]

Summary: Background: Studies have shown proximal diffusion of injected drugs in perineural blocks; such diffusion may affect specificity of the nerve block. Objectives: To investigate the effect of a compression bandage applied to the pastern region on proximal diffusion of contrast medium injected over the palmar digital nerves. Study design: Experimental study, randomised cross‐over design. Methods: Radiodense contrast medium was injected over the lateral and medial palmar digital nerves of the left front limb of nine mature horses. Each horse was injected on two separate occasions, once with a 5 cm wide compression bandage applied proximal to the injection site and once without. The order of the two treatments was randomised with a wash‐out period between treatments of at least 7 days. Radiographs were obtained at 5, 10, 20 and 30 min and distribution of the contrast column assessed. Results: Proximal distribution of the contrast medium was significantly reduced (P<0.01) with compression bandage. Furthermore, the compression bandage inhibited lymphatic drainage of the injected contrast medium. Main limitations: Clinical effect of the differences in diffusion length was not assessed. Conclusions: The compression bandage reduced proximal diffusion and lymphatic drainage of contrast material causing it to stay localised around the injection site. Use of compression bandages could thus result in increased specificity of the nerve block and potentially prolong its effect. [ABSTRACT FROM AUTHOR]

We compare electron and UV observations mapping to the same location in Jupiter's northern polar region, poleward of the main aurora, during Juno perijove 5. Simultaneous peaks in UV brightness and electron energy flux are identified when observations map to the same location at the same time. The downward energy flux during these simultaneous observations was not sufficient to generate the observed UV brightness; the upward energy flux was. We propose that the primary acceleration region is below Juno's altitude, from which the more intense upward electrons originate. For the complete interval, the UV brightness peaked at ~240 kilorayleigh (kR); the downward and upward energy fluxes peaked at 60 and 700 mW/m2, respectively. Increased downward energy fluxes are associated with increased contributions from tens of keV electrons. These observations provide evidence that bidirectional electron beams with broad energy distributions can produce tens to hundreds of kilorayleigh polar UV emissions. Plain Language Summary: Jupiter's ultraviolet (UV) aurora is produced by electrons that precipitate into the planet's atmosphere and interact with hydrogen molecules. A number of different UV auroral emission regions have been identified such as the main aurora, the aurora associated with Jupiter's satellites, and the polar aurora located poleward of the main aurora. We examine electron and UV observations from Juno in Jupiter's northern polar region to investigate the processes responsible for producing Jupiter's polar aurora. We show electrons and UV emissions having simultaneous enhancements during a time when they map to the same location of Jupiter's upper atmosphere at the same time. We present evidence that electrons with energies between 0.1 and 100 kilo electron volts (keV) are capable of producing the polar UV emissions studied here and that further acceleration of these electrons may be occurring at altitudes below the spacecraft. Key Points: Simultaneous peaks are observed in electron energy flux and UV brightness when they map to same location in Jupiter's polar region at the same timeUpward greater than downward electron energy fluxes are observed, suggesting that primary acceleration region may be below ~1.5 jovian radiiDownward energy fluxes able to produce tens to hundreds of kilorayleigh polar UV emissions are identified; increases in energy flux due to tens of keV electrons [ABSTRACT FROM AUTHOR]

Summary: Background: The main criteria for lameness assessment in horses are head movement for forelimb lameness and pelvic movement for hindlimb lameness. However, compensatory head nod in horses with primary hindlimb lameness is a well‐known phenomenon. This compensatory head nod movement can be easily misinterpreted as a sign of primary ipsilateral forelimb lameness. Therefore, discriminating compensatory asymmetries from primary directly pain‐related movement asymmetries is a prerequisite for successful lameness assessment. Objectives: To investigate the association between head, withers and pelvis movement asymmetry in horses with induced forelimb and hindlimb lameness. Study design: Experimental study. Methods: In 10 clinically sound Warmblood riding horses, forelimb and hindlimb lameness were induced using a sole pressure model. The horses were then trotted on a treadmill. Three‐dimensional optical motion capture was used to collect kinematic data from reflective markers attached to the poll, withers and tubera sacrale. The magnitude and side (left or right) of the following symmetry parameters, vertical difference in minimum position, maximum position and range‐up were calculated for head, withers, and pelvis. Mixed models were used to analyse data from induced forelimb and hindlimb lameness. Results: For each mm increase in pelvic asymmetry in response to hindlimb lameness induction, withers movement asymmetry increased by 0.35–0.55 mm, but towards the contralateral side. In induced forelimb lameness, for each mm increase in head movement asymmetry, withers movement asymmetry increased by 0.05–0.10 mm, in agreement with the head movement asymmetry direction, both indicating lameness in the induced forelimb. Main limitations: Results must be confirmed in clinically lame horses trotting overground. Conclusions: The vertical asymmetry pattern of the withers discriminated a head nod associated with true forelimb lameness from the compensatory head movement asymmetry caused by primary hindlimb lameness. Measuring movement symmetry of the withers may, thus, aid in determining primary lameness location. [ABSTRACT FROM AUTHOR]

The Cassini spacecraft orbited Saturn from 2004 to 2017, and in 2006 it started exploring the deep magnetotail, reaching distances of about 68 RS (where RS is the equatorial radius of Saturn). Since Cassini covered a broad area of Saturn's magnetosphere, this raises the question of what is the typical and atypical plasma composition in different regions of Saturn's environment. In this paper, we present a survey of the bulk plasma composition using time‐of‐flight data from the Plasma Spectrometer/Ion Mass Spectrometer instrument on Cassini, from 2004 through 2012. This is the most comprehensive study ever made of relative abundances of thermal plasma at Saturn, maximizing the use of Cassini's orbital coverage in Saturn's magnetosphere during those years, and, therefore, the sensitivity to seasonal or natural variability of the system. We studied the ratio of counts between ions with E/q≃1.19–21,300 eV/q and mass per charge equal to 2 (either H 2+ or He++) and ionized hydrogen ([(m/q = 2)]/[H+]), and a mixture of ions (H2O+, H3O+, OH+, and O+), known as the water group (W+) and ionized hydrogen ([W+]/[H+]). We present the data as a function of position in the magnetosphere, radial distance and local time, and distance from the planet and longitude with respect to the moons Enceladus, Dione, Rhea, and Titan. We found that the plasma composition in Saturn's magnetosphere presents significant local time asymmetries and variability. Key Points: Data show an enhancement in the ratio between ions with mass per charge equal to 2 and protons in the dusk sectorEnhancement is independent of the location of the moons with respect to the spacecraft and of seasonPlasma stagnation point occurs at earlier local time than suggested by previous modeling [ABSTRACT FROM AUTHOR]

Abstract: Reconnection is a fundamentally important process in planetary magnetospheres, with both local and global effects. At Saturn, observations of the magnetotail reconnection site (or x‐line) are rare, with only one in situ encounter reported to date. In this work, an extensive database of plasmoids and dipolarizations (Smith et al., 2016, https://doi.org/10.1002/2015JA022005) was investigated from a multi‐instrument perspective in order to probe the location and variability of the magnetotail x‐line. Several clear intervals were identified in which the x‐line location could be indirectly inferred to move on relatively short timescales. Two case studies are presented, the first of which concerns short‐lived flows, suggesting the reconnection sites can be either short‐lived (∼10 minutes) or extremely azimuthally limited (∼3RS/0.4 hr of local time). The second interval concerns the tailward motion of the reconnection site (or sites), inferred from the increasing electron temperature (and diminishing electron density) associated with the flows. This tailward motion occurs over ∼2.5 hr (approximately a quarter of a planetary rotation). The composition of the suprathermal plasma suggests that this could be an example of the gradual depletion of mass‐loaded flux tubes (that must occur prior to lobe reconnection). These case studies are consistent with previous statistical work that suggested that the site of reconnection in the Kronian magnetotail can be highly dynamic. [ABSTRACT FROM AUTHOR]

Abstract: We present a statistical study of dipolarization fronts within Saturn's magnetotail. Automated methods were used to identify 28 significant southward rotations of the field coupled with enhancements in the electron energy. The observed dipolarizations cover the majority of the magnetotail, though possess a strong dawn‐dusk asymmetry (79% occur postmidnight). Almost half (43%) of dipolarizations occur within 3 hr of another event, though these chains are solely observed postmidnight. Most pitch angle distributions of the heated electron populations show increased relative fluxes parallel or perpendicular to the field, likely due to nonlocal heating effects. The electron temperature and density following the passage of a front are anticorrelated; the temperature increases are accompanied by a decrease in their density. The temperature increases by factors of 4–12, while the density drops by factors of 3–10. Premidnight events consistently show the smallest relative heating and density depletion, suggesting they are observed closer to their generation. In contrast, the location of the postmidnight x‐line is inferred to be more variable, with a large variety of heating factors observed. Forty percent of the events show a strong reduction in water (W+) group fraction, likely related to either the preferential loss of equatorial heavy ions in departing plasmoids or the closure of open field. Two of these events show significant compositional changes suggesting the addition of plasma of external origin; we suggest that these events involved the closure of open field. [ABSTRACT FROM AUTHOR]

Abstract: A new Cassini magnetosheath data set is introduced that is based on a comprehensive survey of intervals in which the observed magnetosheath flow was encompassed within the plasma analyzer field of view and for which the computed numerical moments are therefore expected to be accurate. The data extend from 2004 day 299 to 2012 day 151 and comprise 19,155 416 s measurements. In addition to the plasma ion moments (density, temperature, and flow velocity), merged values of the plasma electron density and temperature, the energetic particle pressure, and the magnetic field vector are included in the data set. Statistical properties of various magnetosheath parameters, including dependence on local time, are presented. The magnetosheath field and flow are found to be only weakly aligned, primarily because of a relatively large z component of the magnetic field, attributable to the field being pulled out of the equatorial orientation by flows at higher latitudes. A new procedure for using magnetosheath properties to estimate the upstream solar wind speed is proposed and used to determine that the amount of electron heating at Saturn's high Mach‐number bow shock is ~4% of the dissipated flow energy. The data set is available as supporting information to this paper. [ABSTRACT FROM AUTHOR]

Abstract: Saturn's largest icy moon, Rhea, hosts a tenuous surface‐sputtered exosphere composed primarily of molecular oxygen and carbon dioxide. In this Letter, we examine Cassini Plasma Spectrometer velocity space distributions near Rhea and confirm that Cassini detected nongyrotropic fluxes of outflowing CO 2 + during both the R1 and R1.5 encounters. Accounting for this nongyrotropy, we show that these possess comparable along‐track densities of ∼2 × 10−3 cm−3. Negatively charged pickup ions, also detected during R1, are surprisingly shown as consistent with mass 26 ± 3 u which we suggest are carbon‐based compounds, such as CN−, C 2 H −, C 2 −, or HCO−, sputtered from carbonaceous material on the moon's surface. The negative ions are calculated to possess along‐track densities of ∼5 × 10−4 cm−3 and are suggested to derive from exogenic compounds, a finding consistent with the existence of Rhea's dynamic CO2 exosphere and surprisingly low O2 sputtering yields. These pickup ions provide important context for understanding the exospheric and surface ice composition of Rhea and of other icy moons which exhibit similar characteristics. [ABSTRACT FROM AUTHOR]

Abstract: Previous research provides evidence that odor is a key driver in food selection in dogs. Dogs' flavor preferences are generally assessed through paired comparison tests based on food intake. Methods for evaluating odor preference in canines are lacking. In this study, the paired comparison test was modified by replacing standard bowls with false‐bottom bowls (FBBs). Made of two compartments separated by a drilled, stainless‐steel plate, FBBs enable odorant compounds to be placed under the food that is presented to the dogs. Several paired comparison trials were conducted on a trained canine panel with FBBs containing various odorant substances under the kibbles. Results showed that dogs were able to perceive the hidden substances and to distinguish between the bowls accordingly. These results demonstrate that the false‐bottom bowl paired comparison method could be helpful in evaluating the role of odor in dogs' food preferences, thus, also as a way of assessing food odor performance. Practical applications: The false‐bottom bowl method is an adaptation of the paired comparison test that enables the influence of odor on dog behavior to be isolated from that stimulated by vision, taste or textural parameters. The odor impact of a hidden substance is tested under pet meal conditions. This new method could be useful in pet food industry to measure the odor potential of a new ingredient, or to understand the key food selection drivers for dogs and cats. In addition, as the olfactory stimulus is not eaten by the animal, the influence of odor in non‐food products for dogs, such as pet care and pet medicines, could also be evaluated using this method. [ABSTRACT FROM AUTHOR]

Abstract: One year's worth of plasma observations from geosynchronous orbit is examined for ion distributions that may simultaneously be subject to the ion Bernstein (IB) instability (generating fast magnetosonic waves) and the Alfvén cyclotron (AC) instability (generating electromagnetic ion cyclotron waves). Confirming past analyses, distributions with robust ∂fp(v⊥)/∂v⊥ > 0 near v|| = 0, which we denote as “ring/shell” distributions, are commonly found primarily on the dayside of the magnetosphere. A new approach to high‐fidelity representation of the observed ring/shell distribution functions in a form readily suited to both analytical moment calculation and linear dispersion analysis is presented, which allows statistical analysis of the ring/shell properties. The ring/shell temperature anisotropy is found to have a clear upper limit that depends on the parallel beta of the ring/shell (β||r) in a manner that is diagnostic of the operation of the AC instability. This upper limit is only reached in the postnoon events, which are primarily produced by the energy‐ and pitch angle‐dependent magnetic drifts of substorm‐injected ions. Further, it is primarily the leading edge of such injections, where the distribution is strongly ring‐like, that the AC instability appears to be operating. By contrast, the ratio of the ring energy to the Alfvén energy remains well within the range of 0.25–4.0 suitable for IB instability throughout essentially all of the events, except those that occur in denser cold plasma of the outer plasmasphere. [ABSTRACT FROM AUTHOR]

Abstract: The ion plasma sheet (~few hundred eV to ~few tens keV) is usually dominated by H+ ions. Here changes in ion composition within the plasma sheet are explored both during individual events and statistically during 54 calm‐to‐storm events and during 21 active‐to‐calm events. Ion composition data from the HOPE (Helium, Oxygen, Proton, Electron) instruments onboard Van Allen Probes satellites provide exceptional spatial resolution and temporal resolution of the H+, O+, and He+ ion fluxes in the plasma sheet. H+ is shown to be the dominant ion in the plasma sheet in the calm‐to‐storm transition. However, the energy‐flux of each ion changes in a quasi‐linear manner during extended calm intervals. Heavy ions (O+ and He+) become increasingly important during such periods as charge‐exchange reactions result in faster loss for H+ than for O+ or He+. Results confirm previous investigations showing that the ion composition of the plasma sheet can be largely understood (and predicted) during calm intervals from knowledge of (a) the composition of previously injected plasma at the onset of calm conditions and (b) use of simple drift‐physics models combined with calculations of charge‐exchange losses. [ABSTRACT FROM AUTHOR]

We present observations of 0.1-100 keV electrons from Juno's Jovian Auroral Distributions Experiment Electron instrument over Jupiter's polar auroral region for periods around four Juno perijoves (PJ1, PJ3, PJ4, and PJ5). The observations reveal regions containing magnetic field aligned beams of bidirectional electrons having broad energy distributions interspersed between beams of upward electrons with narrow, peaked energy distributions, regions void of these electrons, and regions dominated by penetrating radiation. The electrons show evidence of acceleration via parallel electric fields (inverted-V structures) and via stochastic processes (bidirectional distributions). The inverted-V structures shown here were observed from ~1.4 to 2.9 R J and had spatial scales of hundreds to thousands of kilometers along Juno's trajectory. The upward electron energy flux was typically greater than the downward flux, the latter ranging between ~0.01 and 5 mW m−2 for two cases shown here which we estimate could produce ~0.1-50 kR of ultraviolet emission. [ABSTRACT FROM AUTHOR]

A Hot Flow Anomaly (HFA) is created when an interplanetary current sheet interacts with a planetary bow shock. Previous studies have reported observing HFAs at Earth, Mercury, Venus, Mars, and Saturn. During Juno's approach to Jupiter, a number of its instruments operated in the solar wind. Prior to crossing into Jupiter's magnetosphere, Juno observed an HFA at Jupiter for the first time. This Jovian HFA shares most of the characteristics of HFAs seen at other planets. The notable exception is that the Jovian HFA is significantly larger than any HFA seen before. With an apparent size greater than 2 × 106 km the Jovian HFA is orders of magnitude larger than those seen at the other planets. By comparing the size of the HFAs at the other planets with the Jovian HFA, we conclude that HFAs size scales with the size of planetary bow shocks that the interplanetary current sheet interacts with. [ABSTRACT FROM AUTHOR]

Aim In this study, we investigate the impact of altered action potential durations ( APD) on ventricular repolarization time and proarrhythmia in mice with and without genetic deletion of the K+-channel-interacting protein 2 ( KCh IP2−/− and WT respectively). Moreover, we examine the interrelationship between the dispersion of repolarization time and current pulse amplitude in provoking ventricular arrhythmia. Methods Intracardiac pacing in anesthetized mice determined refractory periods and proarrhythmia susceptibility. Regional activation time ( AT), APD and repolarization time (= AT + APD) were measured in isolated hearts using floating microelectrodes. Results Proarrhythmia in WT and KCh IP2−/− was not sensitive to changes in refractory periods. Action potentials were longer in KCh IP2−/− hearts compared to WT hearts. Isolated WT hearts had large apico-basal dispersion of repolarization time, whereas hearts from KCh IP2−/− mice had large left-to-right ventricular dispersion of repolarization time. Pacing from the right ventricle in KCh IP2−/− mice in vivo revealed significant lower current pulse amplitudes needed to induce arrhythmias in these mice. Conclusion Large heterogeneity of repolarization time is proarrhythmic when pacing is delivered from the location of earlier repolarization time. Ventricular repolarization time, location of the pacing stimulus and the amplitude of the stimulating current pulse are critical parameters underlying arrhythmia vulnerability. [ABSTRACT FROM AUTHOR]