In total more than 200 abstracts have been received. A full programme will follow shortly.
Cassini at Titan: What have we learned after more than a decade of observations?
Before Cassini, our understanding of Titan’s interaction with Saturn’s magnetosphere was based on measurements from a single Voyager flyby. Over the past decade, data from over 100 close encounters has challenged that understanding. For example, Cassini discovered that the production of the massive molecules in Titan’s atmosphere begins in the thermosphere, which is strongly altered by Titan’s space environment. Cassini also revealed that Titan’s impact on Saturn’s magnetosphere is weaker, or at least much more subtle, than originally assumed. It is clear that Titan’s environment is complex and variable. The persistent flapping of Saturn’s magnetodisk causes periodic changes in the plasma and field near Titan. On several occasions, Cassini even found Titan outside of Saturn’s magnetosphere in the solar wind. Superimposed on the short-term magnetospheric fluctuations are many-year seasonal and solar cycle changes that only a mission like Cassini could have revealed. In this talk, I will review what we have learned after more than a decade of observations and I will summarize some of the questions that remain.
Magnetosphere-Ionosphere Coupling at the Outer Planets
Magnetosphere-ionosphere coupling is a topic of central significance in understanding the properties of any planetary plasma environment. In this tutorial I will review the basic physics of magnetosphere-ionosphere coupling mechanisms which play a role in the magnetospheres of Jupiter and Saturn. In general terms we are interested in the extent to which the magnetosphere is driven by internal processes (e.g. rapid planetary rotation) versus external mechanisms (e.g. upstream solar wind and interplanetary magnetic field). The extent to which one dominates over the other dictates the nature of the large-scale plasma flows within the magnetosphere. Field-aligned currents are generated in regions of flow shear between the different regimes. The field-aligned currents that flow between the ionosphere and magnetosphere in planetary plasma systems are therefore fundamental to the processes that transfer stress between the magnetosphere and the ionosphere via the planetary magnetic field.
At Earth the momentum is directed from the solar wind and magnetosphere towards the ionosphere. At Jupiter and Saturn it mostly goes the other way. At Saturn our understanding has developed significantly thanks to the high-latitude data from the Cassini mission which have allowed a comprehensive study of the field-aligned currents coupling the magnetosphere to the ionosphere. At Jupiter we have some understanding of how the system is driven, but the new data from Juno will provide the details!
Field-aligned currents observations close to Saturn: Past and present
Gregory Hunt, S. W. H. Cowley, E. J. Bunce, G. Provan, M. K. Dougherty, I. I. Alexeev, E. S. Belenkaya, V. V. Kalegaev, A. J. Coates
We will review recent analyses of azimuthal magnetic field data from the Cassini spacecraft during 2008 showing the presence of field-aligned currents in the midnight local time (LT) sector. These showed that in the southern hemisphere, these currents are found to be strongly modulated in form, magnitude, and position by the phase of the southern planetary period oscillations (PPOs). In the northern hemisphere, however, we show that the currents are modulated by both the northern and southern PPO phases, thus giving the first direct evidence of inter-hemispheric PPO currents. We separate currents independent of PPO phase from the PPO-related currents, by exploiting the expected anti-symmetry of the latter with respect to PPO phase. We find that in both hemispheres the PPO-independent (subcorotation) and PPO-related currents are typically co-located and comparable in magnitude, although this connection is yet to be fully elucidated. These results provide a framework to which the present Grand Finale orbits can be compared to, where Saturn’s auroral field aligned currents are being explored once more. We will assess how the field-aligned currents have evolved in comparison to the above mention framework established from the 2008 dataset. We will extend comparison of LT with these new data. Using both sets of data will inform for the analysis of the Proximal orbits, where a clear understanding of the azimuthal contribution will be critical.
Energetic particle measurements at Jupiter by the Juno-JEDI instrument
George Clark, B. H. Mauk, D. K. Haggerty, C. P. Paranicas, P. Kollmann, A. M. Rymer, S. Bolton, E. J. Bunce, S.w.h Cowley, S. Levin, A. Adriani, F. Allegrini, F. Bagenal, J. E. P. Connerney, R.W. Ebert, G. R. Gladstone, T. Kimura, W. S. Kurth, D. J. McComas, D. Ranquist, J. Saur, J. R. Szalay, and P. W. Valek
As of March 2017, the Juno spacecraft has completed four 53.5 day Jovian polar orbits, with complete science coverage, with an apojove ~110 RJ and a perijove ~1.1 RJ. Thus far, the Jupiter Energetic particle Detector Instrument (JEDI) has been returning a rich and diverse data set that is already challenging our preconceived notions of Jupiter’s magnetosphere and ionosphere. In this talk we will give a brief overview on the recent discoveries made by the JEDI instrument and the unresolved questions that are starting to emerge from the analysis. Specifically, we will briefly discuss Jupiter’s radiation belts, distant plasma sheet observations and the coordinated observations between JEDI, Hisaki and HST. However, a significant portion of this presentation will be dedicated to energetic ion and electron observations over the polar auroral region. These energetic particle populations are observed to have peaked energy distributions consistent with the idea of local acceleration regions containing strong parallel electric fields. The particle phase space spectra suggest the potential drops vary between 100s of kV to ~1 MV. We explore the origin of these strong potential drops within the downward current region by investigating their current-voltage relationship and comparing them to the current theoretical framework on Jovian MI-coupling.
Magnetic Field Measurements and Derivation of Planetary Magnetic Field Models
J. E. P. Connerney
We enter a new era of planetary exploration, with global mapping of magnetic fields overtaking the sparse observations provided by flybys of years past. The challenges associated with derivation of magnetic field models from flyby observations have been addressed with inverse methodologies designed to expose model non-uniqueness. Co-estimation now common in analyses of the Earth’s magnetic field was essential in interpreting early flybys of Jupiter, where spacecraft on equatorial trajectories repeatedly transited the Jovian magnetodisc, a region filled with external ring currents. Models were further improved using field geometric constraints, the most fruitful of which being observations of the Io Flux Tube (IFT) footprint in Jupiter’s ionosphere, north and south. These provide a kind of “ground truth” for planetary magnetic field models, requiring model field geometries to match that illuminated by the electromagnetic induction of orbiting satellites. Other field geometric constraints may be developed using particle absorption signatures, but these have been more limited in scope in application to the outer planets. Some magnetic field models seek to reconcile other observables – such as the frequency and beaming of radio emissions – with magnetic field models, based on explicit models of such phenomena. We’ll try to sort through all the magnetic model monikers (VIP4, VIT4, VIPAL, etc.) and help you understand the differences.
Response of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno
J. D. Nichols, S. V. Badman, F. Bagenal, S. J. Bolton, B. Bonfond, E. J. Bunce, J. T. Clarke, J. E. P. Connerney, S. W. H. Cowley, R. W. Ebert, M. Fujimoto, J.-C. Gérard, G. R. Gladstone, D. Grodent, T. Kimura, W. S. Kurth, B. H. Mauk, G. Murakami, D. J. McComas, G. S. Orton, A. Radioti, T. S. Stallard, C. Tao, P. W. Valek, R. J. Wilson, A. Yamazaki, I. Yoshikawa, ,
We present the first comparison of Jupiter’s auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter’s auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet’s main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter’s magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought.
Variation of ion and electron temperature on Io plasma torus during an outburst measured with Hisaki/EXCEED and gourd-based telescope
Masato Kagitani, Mizuki Yoneda, Ryoichi Koga, Fuminori Tsuchiya, Kazuo Yoshioka, Go Murakami, Tomoki Kimura, Ichiro Yoshikawa
We focus on variability of electron temperature on Io plasma torus (IPT) derived from EUV diagnostics measured by space telescope Hisaki/EXCEED after a volcanic outburst in 2015, as well as ion temperatures parallel and perpendicular to the magnetic field measured from the ground-based spectroscopy. The [SII] observation of IPT was made at Haleakala Observatory from November 2014 through May 2015 with the Echelle spectrograph (R=67,000) coupled to a 40-cm telescope, which enables to enables to measure S+ temperatures parallel and perpendicular to the magnetic field. We also made observation of neutral sodium cloud as a proxy of supply of neutral particles from Io (Yoneda et al., 2015). Based on observation of neutral sodium cloud (Yoneda et al., 2015), neutral supply started to increase at around DOY= 10, was at maximum at around DOY = 50, and has backed into the initial levels at around DOY = 120. In contrast, plasma diagnostics made by Hisaki/EXCEED EUV spectroscopy indicates that hot electron fraction was less than 2 % before DOY = 50, started to increase after DOY = 50, and have reached 8(+/-1) % at DOY = 110. In addition, ion temperatures from ground-based observation started to increase after DOY=50 as similar tread of increase of hot electron fraction. Aurora sudden brightening events were also activated after DOY = 50 as increase of hot electron fraction on the plasma torus. A possible scenario will be discussed on the presentation.
Plasma dynamics around Jupiter’s inner magnetosphere deduced by EUV spectra of the Io plasma torus
Kazuo Yoshioka, Fuminori Tsuchiya, Masato Kagitani, Tomoki Kimura, Go Murakami, Fumiharu, Suzuki, Reina Hikida, Atsushi. Yamazaki, Ichiro. Yoshikawa, Masaki Fujimoto
The EUV emissions from heavy ions in the Io plasma torus is observed by Hisaki, the Earth-orbiting satellite since end of 2013. The radial variation of plasma conditions (electron temperature and ion densities) are deduced through the spectral diagnosis method. The timescales of inward and outward transport of plasmas are also deduced using the physical-chemistry model. These motions may be the result of centrifugally-driven interchange instability (the cold dense plasmas from Io are transported to outward, and the depleted flux tubes which contain hot electrons are transported inwardly). In January 2015, there were large event of volcanic activity on Io. By comparing two data sets during volcanically quiet (November 2013) and active phases (February 2015), we found the drastic change of plasma motions. The velocity increased 2-4 times for both inward and outwards. They correspond to the increase of the neutral source rate caused by the volcanic activity.
Comparing the Magnetospheres of Planets & Massive Stars
Over the past decade a sub-population of hot, massive stars has been discovered to have strong magnetic fields. Many of these magnetic hot stars host 'Centrifugal Magnetospheres' (CMs). CM host stars are typically rapidly rotating, with surface rotational velocities of hundreds of km/s. Their magnetic fields are in general strong (about 10 kG), simple (the majority are well-described by tilted dipoles), and stable (so-called fossil fields, rather than the dynamo fields seen in cool stars such as the Sun). Ions are provided by the star's radiatively driven wind, are confined by its magnetic field, and supported against gravitational infall by centrifugal force. While CMs have some important differences with planetary magnetospheres, there are also numerous similarities. By comparing and contrasting stellar and planetary magnetospheres, I will describe the observational diagnostics used to probe CM properties, and explore the current state of our theoretical understanding, with an emphasis on the open question of the mass leakage mechanism responsible for evacuating plasma from CMs.
How are magnetospheric plasmas heated?
Margaret Galland Kivelson
In a rigorous thermodynamic sense, thermal equilibrium implies isotropic velocity space distributions of Gaussian form but magnetospheric plasmas have loss cones that mess up isotropy and power law tails that depart from Gaussian forms. Ignoring such niceties, we integrate over velocity and equate the average energy per particle with the temperature of a plasma distribution. Thermodynamicians would cringe, but to most magnetospheric physicists, an increase of the average energy per particle measured in the system at rest relative to the bulk flow is regarded as heating. Magnetospheric plasmas gain energy both adiabatically and non-adiabatically. Adiabatic heating comes in different flavors. The first adiabatic invariant requires transverse energy to increase linearly with the magnetic field magnitude; the second adiabatic invariant implies parallel heating through Fermi acceleration as particles bounce along flux tubes shrinking in length. Typically, anisotropy increases with displacement. Non-adiabatic heating can arise through magnetic reconnection, diffusion, such as that connected with interchange instabilities, ionization of neutrals followed by ion pickup, and charge exchange between neutrals and ions. Wave-particle resonances can heat or cool a plasma. Inertial forces, rarely invoked in the terrestrial context, may become significant in rapidly rotating magnetospheres. These concepts will be discussed the magnetospheres of Jupiter and Saturn.
Cassini Measurements of Saturn's Magnetic Field: An Overview
Nicholas Achilleos, Michele K. Dougherty
The Cassini magnetometer (MAG) has provided us with a rich and extensive
dataset of magnetic field measurements, not only of Saturn's internal
field but also the many and varied magnetospheric sources of field
external to the planet. In this review, we will summarise the
development of our understanding in the following main areas:
(1) The apparently high degree of axial symmetry of the planet's
(2) The ubiquitous 'planetary period oscillations' in the field,
themselves a signature of rotating current systems likely driven by an
(3) The finite lifetime of 'fossil fields' in Titan's ionosphere, and
the role of these fields as a signature of previous magnetic / plasma
environments to which Titan has been exposed - with obvious application
to transitions between magnetosphere and solar wind.
The role of the solar wind for the outer planet magnetospheres
Magnetospheric dawn/dusk asymmetries are, fundamentally, linked to the solar wind interaction. At Earth, the dominance of sunward, solar wind-driven flows via a Dungey cycle of reconnection leads to an asymmetric corotating plasmasphere contained within the magnetospheric cavity. Magnetospheric flows at Jupiter and Saturn, on the other hand, are dominated by corotation with the solar wind playing a minor role when adopting the terrestrial corotation/convection model. Nevertheless, Jupiter and Saturn exhibit significant dawn/dusk asymmetries. Following the New Horizons Jupiter flyby, the solar wind interaction at Jupiter and Saturn has been vigorously debated. Key aspects of this debate include large-scale magnetic reconnection vs. some unspecified tangential drag at the magnetopause boundary, generating a viscous-like interaction. Recent studies have demonstrated that the Kelvin Helmholtz instability causes tangential drag via intermittent and small-scale reconnection – a key component of mass, momentum, and energy transport at the magnetopause boundary. Burkholder et al.,  showed that reduced magnetosheath flows on Saturn’s dawn flank are consistent significant momentum transport at the magnetopause boundary, confirming an active solar wind interaction. This tutorial presentation will present a broad overview of the solar wind interaction at Jupiter and Saturn, including different perspectives from data (including Juno observations), theory, and modeling.
Pulsations in Saturn’s magnetosphere
Benjamin Palmaerts, Elias Roussos, Aikaterini Radioti, Denis Grodent, Norbert Krupp
The in-situ exploration of the magnetospheres of Jupiter and Saturn has revealed various pulsed phenomena, some of them being periodic. In Saturn’s magnetosphere, several studies have reported pulsations with a periodicity of around one hour in the measurements of charged particle fluxes, plasma wave emissions, magnetic field strength and auroral emission brightness. A Cassini multi-instrument overview of these hourly pulsations will be presented. A survey of the quasi-periodic 1-hour energetic electron injections observed in Saturn's outer magnetosphere has been achieved together with an analysis of simultaneous pulsations in the low-frequency radio emissions and in the magnetic field. Quasi-periodic 1-hour brightening of auroral structures associated with magnetopause reconnection has been also reported. Pulsed high-latitude lobe reconnection is a likely common triggering process for brightening of a polar auroral spot associated with the cusp and the high-latitude electron pulsations. Finally, the involvement of magnetopause reconnection in the generation of the quasi-periodic electron injections will be discussed.
Radio emissions from Jupiter
I will try to place the recent results from Juno and ground-based decameter observations on the broader perspective of our present knowledge of Jupiter's low-frequency (kilometer to decameter wave) radio emissions.
I will conclude with open questions.
Plasma Observations in Jupiter’s Polar Magnetosphere from the Jovian Auroral Distributions Experiment (JADE)
R. W. Ebert, P. W. Valek, F. Allegrini, F. Bagenal, S. J. Bolton, J. E. P. Connerney, T. K. Kim, S. Levin, P. Louarn, C. E. Loeffler, D. J. McComas, C. Pollock, D. Ranquist, M. Reno, J. R. Szalay, M. F. Thomsen, S. Weidner, R. J. Wilson, and J. L. Zink
Juno crossed Jupiter’s bow shock on 24 June, 2016 at 128 Jovian radii. The spacecraft proceeded to traverse Jupiter’s dawn magnetosphere before being inserted into a 53-day polar orbit around Jupiter on 5 July, 2016. The first science perijove (PJ1) occurred on 27 August, 2016, providing the first opportunity to make in situ measurements of Jupiter’s polar magnetosphere while remotely observing Jupiter’s aurora. Observations of the plasma environment were obtained by the Jovian Auroral Distributions Experiment (JADE; McComas et al. 2013). JADE is a suite of plasma sensors consisting of one ion sensor (JADE-I) and two nearly identical electron sensors (JADE-E) that are designed to measure 0.01 to 46 kilo-electron volts per charge (keV/q) ions with masses < 64 amu/q and 0.1 – 100 keV electrons, including their pitch angle distributions with up to 1 s resolution. In this presentation, we highlight observations from JADE during PJ1 and subsequent perijoves (PJ3, PJ4, PJ5). JADE observations during these perijove passes provided a wealth of new information on the plasma environment in Jupiter’s polar magnetosphere including mono- and bi-directional field aligned electron beams and loss cone features, low-energy (<100 eV) protons, and heavy ions that magnetically map to the Io plasma torus and Jupiter’s plasma sheet. We provide an overview of these observations and briefly discuss their implications for our understanding of Jupiter’s magnetosphere.
Saturn's radiation belts after 13 years of Cassini MIMI/LEMMS observations
Elias Roussos, Peter Kollmann, Norbert Krupp, Chris Paranicas, Donald Mitchell, Stamatios Krimigis, Thomas Armstrong
The Cassini MIMI instrument suite and its energetic particle detector LEMMS have been exploring Saturn’s radiation belts since July 2004, completing nearly 200 crossings through them until June 2017. Besides constructing detailed radiation belt maps, this extensive survey allowed us also to capture the system’s dynamics and its characteristic time scales of variability, revealing also the source processes associated with the production or acceleration of MeV electrons and ions. Furthermore, we found that measurements in the radiation belts can be diagnostic for the global state of Saturn’s magnetosphere and for geophysical aspects of the planet’s moon and ring system. In this review talk we summarise the major findings resulting from MIMI/LEMMS observations in the planet’s radiation belts, focusing on the MeV particle populations. We show that the structure and dynamical evolution of the electron and ion components of the radiation belts is weakly coupled and how the study of each component provides different insights into the magnetosphere, the planet, its moons and rings. We will also discuss some of the early findings from Cassini’s Proximal Orbits, focusing particularly on the question of whether an energetic particle population exists permanently inside the D-ring and if yes, what its potential source processes are.
Interactions of moon atmospheres and interiors with the giant planets' magnetospheres
In our presentation we review basic physics of the electromagnetic interaction of the giant planet’s moons with their surrounding magnetized plasmas. We also discuss implications on the existence of electrically conductive oceans within Jupiter’s moons based on a reinterpretation of Galileo spacecraft measurements and Hubble Space Telescope observations of the moons auroral emissions. The large moons of the giant planets’ are exposed to the time-variable flow of magnetized plasmas. The moons, their atmospheres and magnetic fields are thereby mechanical and electromagnetic obstacles to the flow of these magnetized plasmas. The flow past the obstacles causes momentum exchange, which is the root cause of the interaction. As a result large magnetic field and plasma perturbations are driven, which modify the plasma locally and which partially propagate away from the moons within Alfvén wings to produce auroral effects within the planets’ atmospheres. Time-variable magnetic fields also induce electric fields, which generate electric currents in subsurface oceans and in electrically conductive ionospheres. Observational constraints for these interactions come from in-situ plasma and field observations and from telescope observations of its auroral properties.
Early Results from the Juno Mission
Scott Bolton, Jack Connerney, Steve Levin and the Juno Science Team
Juno is the first mission to investigate Jupiter using a close polar orbit. The Juno science goals include the study of Jupiter interior composition and structure, deep atmosphere and its polar magnetosphere. All orbits have perijove at approximately 5000 km above Jupiter’s visible cloud tops. The payload consists of a set of microwave antennas for deep sounding, magnetometers, gravity radio science, low and high energy charged particle detectors, plasma
wave antennas, ultraviolet imaging spectrograph, infrared imager and spectrometer and a visible camera. The Juno mission design, an overview of the early science results from Juno with an emphasis on results related to the magnetosphere, and a description of the collaborative Earth
based campaign will be presented.
Planetary period oscillations in Saturn's magnetosphere
Stanley W H Cowley and G Provan
One of the principal findings of the Cassini mission has been the ubiquitous presence of modulations near the planetary rotation period in essentially all magnetospheric parameters in the Saturn system. We review the present state of knowledge based on ~14 years of Cassini observations, bringing the story up to date with the latest data.
Auroral explosion at Jupiter observed by the Hisaki satellite and Hubble Space Telescope during approaching phase of the Juno spacecraft
T. Kimura, J. D. Nichols, R. L. Gray, C. Tao, G. Murakami, A. Yamazaki, S. V. Badman, F. Tsuchiya, K. Yoshioka, H. Kita, D. Grodent, G. Clark, I. Yoshikawa, and M. Fujimoto
The continuous monitoring with the Hisaki satellite and Hubble Space Telescope (HST) discovered the transient auroral emission at Jupiter when the solar wind was relatively quiet, which would be associated with the disturbance that spans from the inner to outer magnetosphere. However, the temporal sequence of the magnetospheric disturbance is not resolved yet because we still lack the continuous monitoring. Here we report the coordinated observation made by Hisaki and HST in mid-2016. On day 142, Hisaki detected the onset of the transient aurora when the HST imaging was indicative of the large dawn storm. The outer emission followed the dawn storm within less than ~20 hours. The Hisaki monitoring for the torus indicated that the hot plasma appeared in the torus during the transient aurora. These results imply that the disturbance is initiated at the outer/middle magnetosphere and rapidly expands toward the inner magnetosphere, accompanying the hot plasma injection at the torus.
The Auroral Dynamic Duo - Jupiter's Independent Pulsating X-ray Hot Spots
William R. Dunn, Graziella Branduardi-Raymont, Licia Ray, Caitriona M. Jackman, Ralph P. Kraft, Ron F. Elsner, I. Jonathan Rae, Zhonghua. Yao, Marissa. F. Vogt, G. Randy Gladstone, Glenn S. Orton, James A. Sinclair, Peter G. Ford, Georgina A. Graham, Raquel Caro-Carretero, Andrew J. Coates, Geraint H. Jones
Jupiter’s Northern soft X-ray aurora is concentrated into a polar hot spot that is characterised by spectral lines of precipitating ~MeV ions [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These highly energetic emissions exhibit pulsations on timescales of several 10s of minutes and change morphology, intensity and precipitating particle populations with changing solar wind conditions [Dunn et al. 2016; Kimura et al. 2016]. This may be expected based on their location poleward of the main UV emission, in regions where magnetic field lines map [Vogt et al. 2015] to the noon-dusk outer magnetosphere and/or magnetopause [Kimura et al. 2016].
We present XMM-Newton and Chandra X-ray observations from Summer 2016 (during Juno approach) and Spring 2007 (during New Horizons approach), when the observing geometry provided good visibility of Jupiter’s South Pole. These observations reveal that Jupiter’s Northern and Southern X-ray aurora both appear to be concentrated into persistent hot spots. However, X-ray timing analysis suggests that, for these observations, Jupiter’s Northern and Southern polar X-ray aurora behave independently.
We finish by outlining upcoming XMM-Newton X-ray campaigns and seeking feedback on how best to utilise the opportunities that the next few years offer, in order to understand precisely what drivers generate Jupiter’s X-ray aurora and what the implications of this are for Jupiter’s global magnetospheric dynamics.