Saturn's Plasmapause: Signature of Magnetospheric Dynamics

We explore the paradigm that Saturn's plasmapause marks the boundary between the magnetic flux tubes that have been circulating around the planet for some time, accumulating a dense load of Enceladus‐sourced material, and those that have recently undergone tail reconnection, shedding the bulk of the cold plasma and retaining a more tenuous, heated population. A centrifugally‐driven interchange instability should develop at this boundary, producing fingers of outward‐propagating dense plasma and of inward‐propagating hot, tenuous plasma. The plasmapause should thus be identifiable as a transition from mostly‐dense‐with‐some‐tenuous to mostly‐tenuous‐with‐some‐dense plasma populations. Electron densities from the Cassini CAPS/ELS instrument are used to identify the location of this transition for all of the low‐latitude (<5° from the magnetic equator) passes through Saturn's inner/middle magnetosphere. The boundary is typically found near and somewhat beyond L=10 (i.e., at ~10 Rs from the planet), with a local time asymmetry such that it is closer to the planet on the night side than on the day side

Cassini observations of the thermal plasma in the vicinity of Saturn's main rings and the F and G rings

The ion mass spectrometer on Cassini detected enhanced ion flux near Saturn's main rings that is consistent with the presence of atomic and molecular oxygen ions in the thermal plasma. The ring "atmosphere'' and "ionosphere'' are likely produced by UV photosputtering of the icy rings and subsequent photoionization of O-2. The identification of the O+ and O-2(+) ions is made using time-of-flight analysis and densities and temperatures are derived from the ion counting data. The ion temperatures over the main rings are a minimum near synchronous orbit and increase with radial distance from Saturn as expected from ion pick up in Saturn's magnetic field. The O-2(+) temperatures provide an estimate of the neutral O-2 temperature over the main rings. The ion mass spectrometer also detected significant O-2(+) outside of the main rings, near the F ring. It is concluded that between the F and G rings, the heavy ion population most likely consists of an admixture of O-2(+) and water group ions O+, OH+, and H2O+

Cassini detection of Enceladus' cold water-group plume ionosphere

This study reports direct detection by the Cassini plasma spectrometer of freshly-produced water-group ions (O+, OH+, H2O+, H3O+) and heavier water dimer ions (HxO(2))(+) very close to Enceladus where the plasma begins to emerge from the plume. The data were obtained during two close ( 52 and 25 km) flybys of Enceladus in 2008 and are similar to ion data in cometary comas. The ions are observed in detectors looking in the Cassini ram direction exhibiting energies consistent with the Cassini speed, indicative of a nearly stagnant plasma flow in the plume. North of Enceladus the plasma slowing commences about 4 to 6 Enceladus radii away, while south of Enceladus signatures of the plasma interaction with the plume are detected 22 Enceladus radii away. Citation: Tokar, R. L., R. E. Johnson, M. F. Thomsen, R. J. Wilson, D. T. Young, F. J. Crary, A. J. Coates, G. H. Jones, and C. S. Paty ( 2009), Cassini detection of Enceladus' cold water-group plume ionosphere, Geophys. Res. Lett., 36, L13203, doi:10.1029/2009GL038923

Survey of pickup ion signatures in the vicinity of Titan using CAPS/IMS

Pickup ion detection at Titan is challenging because ion cyclotron waves are rarely detected in the vicinity of the moon. In this work, signatures left by freshly produced pickup heavy ions (m/q ∼ 16 to m/q ∼ 28) as detected in the plasma data by the Cassini Plasma Spectrometer/Ion Mass Spectrometer (CAPS/IMS) instrument on board Cassini are analyzed. In order to discern whether these correspond to ions of exospheric origin, one of the flybys during which the reported signatures were observed is investigated in detail. For this purpose, ion composition data from time-of-flight measurements and test particle simulations to constrain the ions' origin are used. After being validated, the detection method is applied to all the flybys for which the CAPS/IMS instrument gathered valid data, constraining the region around the moon where the signatures are observed. The results reveal an escape region located in the anti-Saturn direction as expected from the nominal corotation electric field direction. These findings provide new constraints for the area of freshly produced pickup ion escape, giving an approximate escape rate of inline image ions· s−1

Magnetic signatures of plasma-depleted flux tubes in the Saturnian inner magnetosphere

Initial Cassini observations have revealed evidence for interchanging magnetic flux tubes in the inner Saturnian magnetosphere. Some of the reported flux tubes differ remarkably by their magnetic signatures, having a depressed or enhanced magnetic pressure relative to their surroundings. The ones with stronger fields have been interpreted previously as either outward moving mass-loaded or inward moving plasma-depleted flux tubes based on magnetometer observations only. We use detailed multi-instrumental observations of small and large density depletions in the inner Saturnian magnetosphere from Cassini Rev. A orbit that enable us to discriminate amongst the two previous and opposite interpretations. Our analysis undoubtedly confirms the similar nature of both types of reported interchanging magnetic flux tubes, which are plasma-depleted, whatever their magnetic signatures are. Their different magnetic signature is clearly an effect associated with latitude. These Saturnian plasma-depleted flux tubes ultimately may play a similar role as the Jovian ones

Cassini in situ observations of long duration magnetic reconnection in Saturn’s magnetotail

Magnetic reconnection is a fundamental process in solar system and astrophysical plasmas, through which stored magnetic energy associated with current sheets is converted into thermal, kinetic and wave energy1, 2, 3, 4. Magnetic reconnection is also thought to be a key process involved in shedding internally produced plasma from the giant magnetospheres at Jupiter and Saturn through topological reconfiguration of the magnetic field5, 6. The region where magnetic fields reconnect is known as the diffusion region and in this letter we report on the first encounter of the Cassini spacecraft with a diffusion region in Saturn’s magnetotail. The data also show evidence of magnetic reconnection over a period of 19?h revealing that reconnection can, in fact, act for prolonged intervals in a rapidly rotating magnetosphere. We show that reconnection can be a significant pathway for internal plasma loss at Saturn6. This counters the view of reconnection as a transient method of internal plasma loss at Saturn5, 7. These results, although directly relating to the magnetosphere of Saturn, have applications in the understanding of other rapidly rotating magnetospheres, including that of Jupiter and other astrophysical bodies

Internally driven large-scale changes in the size of Saturn's magnetosphere

Saturn’s magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system’s dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma-loaded” or “plasma-depleted” states, defined in terms of the internal suprathermal plasma pressure

Cognitive Dysfunction in Non-Alcoholic Fatty Liver Disease—Current Knowledge, Mechanisms and Perspectives

Non-alcoholic fatty liver disease (NAFLD) has emerged as the hepatic component of the metabolic syndrome and now seemingly affects one-fourth of the world population. Features associated with NAFLD and the metabolic syndrome have frequently been linked to cognitive dysfunction, i.e. systemic inflammation, vascular dysfunction, and sleep apnoea. However, emerging evidence suggests that NAFLD may be a cause of cognitive dysfunction independent of these factors. NAFLD in addition exhibits dysbiosis of the gut microbiota and impaired urea cycle function, favouring systemic ammonia accumulation and further promotes systemic inflammation. Such disruption of the gut–liver–brain axis is essential in the pathogenesis of hepatic encephalopathy, the neuropsychiatric syndrome associated with progressive liver disease. Considering the growing burden of NAFLD, the morbidity from cognitive impairment is expected to have huge societal and economic impact. The present paper provides a review of the available evidence for cognitive dysfunction in NAFLD and outlines its possible mechanisms. Moreover, the clinical challenges of characterizing and diagnosing cognitive dysfunction in NAFLD are discussed

Imaging in the time of NFD/NSF: do we have to change our routines concerning renal insufficiency?

To date there are potential chronology-based but not conclusive reasons to believe that at least some of the gadolinium complexes play a causative role in the pathophysiology of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). Still, the exact pathogenesis and the risk for patients is unclear beside the obvious connection to moderate to severe renal insufficiency. So far, MR imaging with Gd-enhancement was regarded as the safest imaging modality in these patients—the recent development creates tremendous uncertainty in the MR-community. Nevertheless, one should remember that, despite the over 200 cases of NSF and about 100 with proven involvement of Gd3+, the vast majority of over 200 million patients exposed to gadolinium since the 1980s have tolerated these agents well. Importantly, NSF is a rare disease and does not appear to occur in patients without renal impairment. Many patients and researchers have undergone MR investigations with Gd exposure in the past. For those, it is essential to know about the safety of the agents at normal renal function. We can hope that pharmacoepidemiological and preclinical studies will allow us to better understand the pathophysiology and role of the various MR contrast agents in the near future

Internally driven large-scale changes in the size of Saturn's magnetosphere

Saturn’s magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system’s dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma-loaded” or “plasma-depleted” states, defined in terms of the internal suprathermal plasma pressure