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We compare Chandra and XMM-Newton X-ray observations of Jupiter during 2007 with a rich multi-instrument data set including upstream in situ solar wind measurements from the New Horizons spacecraft, radio emissions from the Nancay Decametric Array and Wind/Waves, and ultraviolet (UV) observations from the Hubble Space Telescope. New Horizons data revealed two corotating interaction regions (CIRs) impacted Jupiter during these observations. Non-Io decametric bursts and UV emissions brightened together and varied in phase with the CIRs. We characterize three types of X-ray aurorae: hard X-ray bremsstrahlung main emission, pulsed/flared soft X-ray emissions, and a newly identified dim flickering (varying on short time scales, but quasi-continuously present) aurora. For most observations, the X-ray aurorae were dominated by pulsed/flaring emissions, with ion spectral lines that were best fit by iogenic plasma. However, the brightest X-ray aurora was coincident with a magnetosphere expansion. For this observation, the aurorae were produced by both flickering emission and erratic pulses/flares. Auroral spectral models for this observation required the addition of solar wind ions to attain good fits, suggesting solar wind entry into the outer magnetosphere or directly into the pole for this particularly bright observation. X-ray bremsstrahlung from high energy electrons was only bright for one observation, which was during a forward shock. This bremsstrahlung was spatially coincident with bright UV main emission (power > 1 TW) and X-ray ion spectral line dusk emission, suggesting closening of upward and downward current systems during the shock. Otherwise, the bremsstrahlung was dim, and UV main emission power was also lower (

International audience; Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to ~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (J. Outside that region, the >100-keV electrons contribute to most (>~70-80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.

We analyze plasma ion observations from the Solar Wind Around Pluto instrument on New Horizons as it traveled back through the dusk flank of the Jovian magnetotail from ~600 to more than 2500 Jovian radii behind the planet. We find that at all distances, light ions (mostly protons) dominate the heavy ions (S++ and O+) that are far more abundant in the near Jupiter plasma disk and that were expected to be the primary ions filling the Jovian magnetotail. This key new observation might indicate that heavy ions are confined closer to the equator than the spacecraft trajectory or a substantial addition of light ions via reconnection and/or mixing along the magnetopause boundary. However, because we find no evidence for acceleration of the tail plasma with distance, a more likely explanation seems to be that the heavy ions are preferentially released down the dawn flank of the magnetotail. Perhaps, this occurs as a part of the process where flux tubes, after expanding as they rotate across the near‐tail region, need to pull back inward in order to fit within the dawnside of the magnetopause. A second major finding of this study is that there are two dominant periods of the plasma structures in the Jovian magnetotail: 3.53 (0.18 full width at half maximum (FWHM)) and 5.35 (0.38 FWHM) days. Remarkably, the first of these is identical within the errors to Europa's orbital period (3.55 days). Both of these results should provide important new fodder for Jovian magnetospheric theories and lead to a better understanding of Jupiter's magnetosphere.

Carbon foils have been successfully used for several decades in space plasma instruments to detect ions and neutral atoms. These instruments take advantage of two properties of the particle-foil interaction: charge conversion of neutral atoms and/or secondary electron emission. This interaction also creates several adverse effects for the projectile exiting the foil, such as angular scattering and energy straggling, which usually act to reduce the sensitivity and overall performance of an instrument. The magnitude of these effects mainly varies with the incident angle, energy, and mass of the incoming projectile and the foil thickness. In this paper, we describe these effects and the properties of the interaction. We also summarize results from recent studies with graphene foils, which can be made thinner than carbon foils due to their superior strength. Graphene foils may soon replace carbon foils in space plasma instruments and open new opportunities for space research in the future.

This study provides the first observations of Plutogenic ions and their unique interaction with the solar wind. We find ~20% solar wind slowing that maps to a point only ~4.5 RP upstream of Pluto and a bow shock most likely produced by comet-like mass loading. The Pluto obstacle is a region of dense heavy ions bounded by a “Plutopause” where the solar wind is largely excluded and which extends back >100 RP into a heavy ion tail. The upstream standoff distance is at only ~2.5 RP. The heavy ion tail contains considerable structure, may still be partially threaded by the interplanetary magnetic field (IMF), and is surrounded by a light ion sheath. The heavy ions (presumably CH4+) have average speed, density, and temperature of ~90 km s−1, ~0.009 cm−3, and ~7 × 105 K, with significant variability, slightly increasing speed/temperature with distance, and are N-S asymmetric. Density and temperature are roughly anticorrelated yielding a pressure ~2 × 10−2 pPa, roughly in balance with the interstellar pickup ions at ~33 AU. We set an upper bound of

Juno's Jupiter Energetic particle Detector Instrument (JEDI) often detects energetic electron beams over Jupiter's polar regions. In this paper, we document a subset of intense magnetic field-aligned beams of energetic electrons moving away from Jupiter at high magnetic latitudes both north and south of the planet. The number fluxes of these beams are often dominated by electrons with energies above about 1 MeV. These very narrow beams can create broad angular responses in JEDI with unique signatures in the detector count rates, probably because of >10 MeV electrons. We use these signatures to identify the most intense beams. These beams occur primarily above the swirl region of the polar cap aurora. This polar region is described as being of low brightness and high absorption and the most magnetically "open" at Jupiter.

Jupiter's nightside magnetosphere stretches out into an extensive magnetotail. New Horizons observed continuously over 1 AU down Jupiter's tail, far more than any other spacecraft. Previously, Voyager 2 showed signatures of the tail as far as 4 AU distance from Jupiter. We combine data from New Horizons' charged particle instruments: Solar Wind Around Pluto, measuring plasma ions (21–7800 eV/Q), and Pluto Energetic Particle Spectrometer Science Investigation, measuring energetic ions and electrons (0.03–1.6 MeV). The magnetosheath is clearly distinguished from the magnetotail, owing to more plasma ions. They are often separated by a boundary layer with intermediate properties at plasma energies but resemblance to the magnetotail at higher energies. Compared to the tail, the sheath contains on average more energetic protons and helium ions (potential solar wind origin) and fewer energetic electrons, oxygen, and sulfur ions (latter two of magnetospheric origin). The difference between tail and sheath for energetic ions and electrons is less pronounced than for plasma ions, which may result from particle exchange. We have ruled out that this is due to gyroradius. Energetic ion count rate enhancements with velocity dispersion cross between tail, boundary layer, and sheath. This indicates occasional magnetic connections since the enhancements are interpreted as particles following magnetic flux tubes. The deep tail magnetic field is therefore not entirely separated from the solar wind. Brief magnetic connection will mostly allow the fastest particles to cross, in agreement with the observations. Most dispersed enhancements include sulfur ions consistent with an origin near Jupiter's X line. We found one event of mostly protons, indicating an origin at larger distances.

Observations of Jovian magnetopause crossing by a number of different spacecraft have established that Jupiter's magnetosphere has a generally bimodal size distribution, with typical standoff distances at the nose of ~63 and ~92 RJ. Here we examine both the external solar wind structure and time constants and the internal magnetospheric time constants for shedding and refilling material in the Jovian plasma disk. We show that these latter time constants are ~ hours to ~10 h, comparable to the compression time of the magnetopause, but shorter than the typically several day expansion time when the solar wind dynamic pressure decreases. Together, we show that it is the well-developed compressions and rarefactions in the solar wind at ~5 AU that produced the generally bimodally structured solar wind dynamic pressure and hence Jovian magnetospheric size.

[1] We report on plasma observations along Jupiter's dusk magnetospheric flank from ∼1625 to 2550 RJ using measurements from the Solar Wind Around Pluto instrument onboard New Horizons (NH). NH observed 16 magnetopause crossings between 1654 and 2429 RJ that were identified by transitions between magnetotail/boundary layer and magnetosheath plasma. These transitions were either sharp, with the magnetopause clearly separating two distinct plasma regimes, or comparatively gradual, where it was difficult to distinguish between different plasma populations. The magnetosheath distributions had high counts, were relatively wide in energy/charge (E/Q), and steadily decreased in speed. Flow speeds in the sheath were always higher (lower) when NH entered (exited) this region. A boundary layer was observed inside of the magnetopause at several crossings. The boundary layer plasma was composed of light ions, and the counts and mean E/Q of these distributions were generally lower than magnetosheath values indicating a lower density and speed. Some of the NH magnetopause crossing locations fell within tail cross-section estimates from model results/observations closer to the planet, though more than half were outside of the largest tail radius estimate. Estimates of angular displacement of the tail boundary compared favorably with a statistical study of near-Jupiter solar wind flow cone angle distributions. We propose that the outward crossings resulted from dawnward deflection and contraction of the tail from forward shocks and compression regions in the near-Jupiter solar wind, and the inward crossings resulted from duskward deflection and tail expansion from the passage of reverse shocks and rarefaction regions.

[1] We examined plasma and magnetic field observations from all three Ulysses polar orbits of the Sun to study the properties of the slow and fast solar wind and interplanetary coronal mass ejections (ICMEs). We derived equations to characterize the radial and latitudinal variations for these three types of heliospheric plasma and identify distinguishing features in their spatial variations. Most notably, the slow-wind proton temperature falls less rapidly with distance than does the fast wind, indicating a source of enhanced heating in the low-speed wind. After removing the radial variations from the measurements, only minor latitudinal gradients were identified. The fast wind has now been shown to be only weakly dependent on solar latitude for two successive solar minima. The spatial variations in the ICME properties do not differ significantly from the slow and fast solar wind, although the variability in their parameters is much larger. We also investigated solar cycle variations in the fast polar coronal hole (PCH) flows by comparing their properties measured over Ulysses' 1st and 3rd orbits. While the latitudinal gradients were similar, slight differences were observed in the radial dependence for the proton density and magnetic field strength. Also, a slight reduction in the proton speed at 1 AU, along with more significant decreases in the proton temperature, density, dynamic pressure, and magnetic field strength, was observed for the 3rd orbit relative to that for the 1st. These results are consistent with recent observations of weaker PCH flows for the current solar minimum.