The Cassini magnetometer has detected the interaction of the magnetospheric plasma of Saturn with an atmospheric plume at the icy moon Enceladus. This unanticipated finding, made on a distant flyby, ...was subsequently confirmed during two follow-on flybys, one very close to Enceladus. The magnetometer data are consistent with local outgassing activity via a plume from the surface of the moon near its south pole, as confirmed by other Cassini instruments.
We infer the evolution of magnetopause reconnection from simultaneous in situ magnetopause crossings and auroral observations by Cassini on 19 July 2008. Depending on the magnetosheath field, it ...proceeds from (i) the high‐latitude lobe, producing a cusp spot in the aurora, to (ii) lower latitude but north of Cassini, evidenced by an enhancement of the pre‐noon auroral arc and escape of magnetospheric electrons during a long boundary layer traversal, to (iii) bursts of reconnection south of Cassini, resulting in bifurcations of the near‐noon auroral oval, escape of magnetospheric electrons, and a short boundary layer encounter. The conditions under which the auroral bifurcations associated with this bursty reconnection were observed were examined for this and three other examples. The magnetosphere was strongly compressed with a high magnetosheath field strength in every case. We conclude that reconnection can proceed at different locations on the magnetopause, depending on the local magnetic shear and plasma β conditions, and bursty reconnection occurs when the magnetosphere is strongly compressed and can result in significant solar wind‐driven flux transport in Saturn's outer magnetosphere.
Key Points
Bursty reconnection occurs when the magnetosphere is strongly compressed
A dependence on plasma beta and magnetic shear is also evident
Significant solar wind‐driven flows will be present under these conditions
We investigate the evolution of the properties of planetary period magnetic field oscillations observed by the Cassini spacecraft in Saturn's magnetosphere over the interval from late 2004 to early ...2011, spanning equinox in mid‐2009. Oscillations within the inner quasi‐dipolar region (L ≤ 12) consist of two components of close but distinct periods, corresponding essentially to the periods of the northern and southern Saturn kilometric radiation (SKR) modulations. These give rise to modulations of the combined amplitude and phase at the beat period of the two oscillations, from which the individual oscillation amplitudes and phases (and hence periods) can be determined. Phases are also determined from northern and southern polar oscillation data when available. Results indicate that the southern‐period amplitude declines modestly over this interval, while the northern‐period amplitude approximately doubles to become comparable with the southern‐period oscillations during the equinox interval, producing clear effects in pass‐to‐pass oscillation properties. It is also shown that the periods of the two oscillations strongly converge over the equinox interval, such that the beat period increases significantly from ∼20 to more than 100 days, but that they do not coalesce or cross during the interval investigated, contrary to recent reports of the behavior of the SKR periods. Examination of polar oscillation data for similar beat phase effects yields a null result within a ∼10% upper limit on the relative amplitude of northern‐period oscillations in the south and vice versa. This result strongly suggests a polar origin for the two oscillation periods.
Key Points
Near rotation period phenomena at Saturn are studied using magnetic field data
We study seasonal changes in both period and amplitude of the oscillations
The result strongly suggests a polar origin for the two oscillation periods
Saturn's internal planetary magnetic field Burton, M. E.; Dougherty, M. K.; Russell, C. T.
Geophysical research letters,
December 2010, Volume:
37, Issue:
24
Journal Article
Peer reviewed
Open access
A model of Saturn's internal planetary magnetic field based on data from the Cassini prime mission has been derived. In the absence of a determination of the rotation rate, the model is constrained ...to be axisymmetric. Non‐axisymmetric models for a range of plausible planetary rotation periods have also been derived and we evaluate upper limits on the asymmetry of the internal magnetic field based on those models. We investigate whether a maximum in the non‐axisymmetric magnetic field can be identified at a particular rotation rate thus providing insight into the rotation rate of the planet's interior. No such peak can unambiguously be identified. An axisymmetric octupole model is adequate to fit the data and addition of higher order terms does not improve the goodness of fit. The largest value of the dipole tilt obtained from non‐axisymmetric models (<0.1°) confirm the high degree of symmetry of Saturn's magnetic field.
Unlocking the code of 14-3-3 Dougherty, Michele K; Morrison, Deborah K
Journal of cell science,
2004-Apr-15, Volume:
117, Issue:
Pt 10
Journal Article
Peer reviewed
Open access
One of the most striking 'rags to riches' stories in the protein world is that of 14-3-3, originally identified in 1967 as merely an abundant brain protein. The first clues that 14-3-3 would play an ...important role in cell biology came almost 25 years later when it was found to interact with various proto-oncogene proteins and signaling proteins. The subsequent identification of 14-3-3 as a phosphoserine/phosphothreonine-binding protein firmly established its importance in cell signaling. 14-3-3 family members are found in all eukaryotes - from plants to mammals - and more than 100 binding partners have been identified to date. The targets of 14-3-3 are found in all subcellular compartments and their functional diversity is overwhelming - they include transcription factors, biosynthetic enzymes, cytoskeletal proteins, signaling molecules, apoptosis factors and tumor suppressors. 14-3-3 binding can alter the localization, stability, phosphorylation state, activity and/or molecular interactions of a target protein. Recent studies now indicate that the serine/threonine protein phosphatases PP1 and PP2A are important regulators of 14-3-3 binding interactions, and demonstrate a role for 14-3-3 in controlling the translocation of certain proteins from the cytoplasmic and endoplasmic reticulum to the plasma membrane. New reports also link 14-3-3 to several neoplastic and neurological disorders, where it might contribute to the pathogenesis and progression of these diseases.
We analyze the radial distribution of electron populations inside 20 Rs in Saturn's magnetosphere, and we calculate moments for these populations by a forward modeling method using composite spectra ...produced by the CAPS/ELS (0.6 eV to 26 keV) and the MIMI/LEMMS (15 keV to 10 MeV) instruments on board Cassini. We first calculate and harmonize both data sets in physical units and apply corrections taking into account biases introduced by spacecraft interaction with the magnetospheric environment. We then test different bimodal isotropic electron distribution models, deciding on a model with two kappa distributions. We adjust our isotropic model to the flux composite spectra with a least square method to produce three sets of fluid parameters (density, temperature, spectral index) per electron population. The radial profiles are then analyzed, revealing a relevant boundary at 9 Rs in both thermal and suprathermal electron populations. Observed discontinuities in the moment profiles (sudden drop‐off in cold density profile outside 9 Rs, hot electrons drop‐off inside 9 Rs) coincide with the known outer edge of Saturn's neutral OH cloud. Farther out, thermal electrons disappear completely beyond 15 Rs while suprathermal electrons are still observed in the middle and outer magnetosphere.
The shape and location of a planetary magnetopause can be determined by balancing the solar wind dynamic pressure with the magnetic and thermal pressures found inside the boundary. Previous studies ...have found the kronian magnetosphere to show rigidity (like that of Earth) as well as compressibility (like that of Jupiter) in terms of its dynamics. In this paper we expand on previous work and present a new model of Saturn's magnetopause. Using a Newtonian form of the pressure balance equation, we estimate the solar wind dynamic pressure at each magnetopause crossing by the Cassini spacecraft between Saturn Orbit Insertion in June 2004 and January 2006. We build on previous findings by including an improved estimate for the solar wind thermal pressure and include low‐energy particle pressures from the Cassini plasma spectrometer's electron spectrometer and high‐energy particle pressures from the Cassini magnetospheric imaging instrument. Our improved model has a size‐pressure dependence described by a power law DP−1/5.0 ± 0.8. This exponent is consistent with that derived from numerical magnetohydrodynamic simulations.
We take the plasma parameters derived by Bagenal et al. (2017) from Voyager plasma science data in the Jovian magnetosphere and examine the radial profiles of density, temperature, composition, and ...azimuthal flow. The plasma sheet shows a relatively uniform structure of decreasing electron density (Ne) and increasing temperature out to about 20 RJ, but beyond about 15 RJ there is increasing disorder with sporadic blobs of cold plasma. These small (~0.5 RJ) blobs of cold (~20 eV) plasma make a minor contribution to the net outward flux of iogenic plasma. The ion composition in the cold blobs is consistent with the ion abundances derived from physical chemistry models extending from 6 to ~9 RJ, whereupon the collisional reactions slow down and radial transport speeds up, effectively freezing in the ion composition to the following abundances: O+/Ne = 15–22%, S++/Ne = 10–19%, O++/Ne = 4–8%, S+++/Ne = 4–6%, and S+/Ne = 1–5%. Beyond about 7 RJ the component of hot (suprathermal, approximately hundreds of eV) ions becomes a significant fraction of the total density. The radial profile of the plasma's azimuthal flow speed shows that corotation begins to breakdown at about 9 RJ, dipping down to about 20% below corotation before increasing back up to corotation briefly (~17–20 RJ), reaching an asymptotic value of about 225 km/s (corresponding to rigid corotation at ~18 RJ). We present a 2‐D model of the plasma sheet beyond 6 RJ based on simple functions for the equatorial profiles of plasma properties and steady state diffusive equilibrium along magnetic flux tubes. Cold plasma blobs in the Jovian plasma sheet show ion composition consistent with physical chemistry models. Azimuthal flow speeds dip below corotation 9–15 Jovian radii. Radial profiles of plasma properties are combined to make a 2‐D model of plasma sheet.
Key Points
Cold plasma blobs in the Jovian plasma sheet show ion composition consistent with physical chemistry models
Azimuthal flow speeds dip below corotation 9–15 Jovian radii
Radial profiles of plasma properties are combined to make a 2‐D model of plasma sheet
When the Voyager 1 and 2 spacecraft flew through the Jovian system in March and July 1979, the Plasma Science instruments measured ions and electrons in the Io plasma torus and plasma sheet between ...4.9 and 42 RJ. The dominant ions in the Jovian magnetosphere comprise the first few ionization states of atomic sulfur and oxygen. We present here an analysis of minor ion species H+, Na+, and SO2+. Protons are 1–20% of the plasma between 5 and 30 RJ with variable temperatures ranging by a factor of 10 warmer or colder than the heavy ions. We suggest that these protons, measured deep inside the magnetosphere, are consistent with a source from the ionosphere of ~1.5–7.5 × 1027 protons s−1 (2.5–13 kg/s). Na+ ions are detected between 5 and 40 RJ at an abundance of 1 to 10%, produced by the ionization of the extended neutral cloud emanating from Io that has been observed since 1974. SO2+ ions are detected between 5.31 and 5.07 RJ at an abundance of 0.1–0.6%. These ions clearly come from the plasma interaction with Io's atmosphere, but the exact processes whereby atmospheric molecules escape Io and end up as ions well inside Io's orbit are not clear.
Key Points
Protons comprise 1‐20% of the plasma between 5 and 30 RJ
Na+ ions are detected between 5 and 40 RJ at an abundance of 1 to 10%
SO2+ ions are detected between 5.31 and 5.07 RJ at an abundance of 0.1‐0.6%
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