J. H. Waite

A pulsating auroral X-ray hot spot on Jupiter

Jupiters X-ray aurora has been thought to be excited by energetic sulphur and oxygen ions precipitating from the inner magnetosphere into the planets polar regions. Here we report high-spatial-resolution observations that demonstrate that most of Jupiters northern auroral X-rays come from a ‘hot spot’ located significantly poleward of the latitudes connected to the inner magnetosphere. The hot spot seems to be fixed in magnetic latitude and longitude and occurs in a region where anomalous infrared and ultraviolet emissions have also been observed. We infer from the data that the particles that excite the aurora originate in the outer magnetosphere. The hot spot X-rays pulsate with an approximately 45-min period, a period similar to that reported for high-latitude radio and energetic electron bursts observed by near-Jupiter spacecraft. These results invalidate the idea that jovian auroral X-ray emissions are mainly excited by steady precipitation of energetic heavy ions from the inner magnetosphere. Instead, the X-rays seem to result from currently unexplained processes in the outer magnetosphere that produce highly localized and highly variable emissions over an extremely wide range of wavelengths.

ROSAT observations of the Jupiter aurora

Rontgen satellite (ROSAT) high-resolution imager (HRI) and position sensitive proportional counter (PSPC) observations of Jupiter obtained in April 1991 and May 1992 reveal soft X ray emissions apparently associated with Jupiters aurora and similar to X ray emissions observed earlier by the Einstein Observatory. The HRI images show emission mainly from Jupiters northern hemisphere at all Jovian longitudes observed, and there is some indication of a longitudinal modulation of the emission in phase with the well-known ultraviolet modulation of the northern aurora. The PSPC data reveal a very soft spectrum. Comparison of the observed spectrum with models for both electron bremsstrahlung radiation and line emission from S and O ions indicates that the line spectrum gives a much better statistical fit to the observed spectrum. The X ray observations presented here therefore support the hypothesis that ion precipitation is the most likely cause of the Jovian X ray emissions, a result first suggested by the Einstein results [Metzger et al., 1983].

Thermal profiles in the auroral regions of Jupiter

The temperature structure within the northern auroral region of Jupiter is studied by reanalyzing the Voyager 1/infrared interferometer and radiometer spectrometer (IRIS) spectra. The total measured excess infrared auroral zone emission (averaged over the IRIS field of view) in the hydrocarbon bands between 7 and 13 μm is found to be about 208 ergs cm−2 s−1 over an area of about 2 × 1018 cm2 with a resulting power output of 4 × 1013 W. In comparison, the total energy deposition by magnetospheric charged particles has been estimated on the basis of UV observations to range between 1 × 1013 and 4 × 1013 W over a comparable area. The large amount of radiated energy observed in the infrared may imply an additional heat source in the auroral regions (possibly Joule heating). A new set of thermal profiles of Jupiters high-latitude upper atmosphere has also been derived. These profiles have a large temperature enhancement in the upper stratosphere and are constrained to reproduce the CH4 emission at 7.7 μm. The emission in the other hydrocarbon bands (C2H2 and C2H6) is found to depend on the depth to which the temperature enhancement extends, which further constrains the thermal profiles. This study shows that a large temperature enhancement in the upper stratosphere and lower thermosphere can explain the observed excess hydrocarbon emission bands; thus smaller variations in hydrocarbon abundances (between the high latitudes and the equatorial and middle latitudes) are required than has been assumed in previous models.

Jupiter Thermospheric General Circulation Model (JTGCM): Global structure and dynamics driven by auroral and Joule heating

(including auroral/Joule heating processes). The resulting JTGCM has been fully spun-up and integrated for � 40 Jupiter rotations. Results from three JTGCM cases incorporating moderate auroral heating, ion drag, and moderate to strong Joule heating processes are presented. The neutral horizontal winds at ionospheric heights vary from 0.5 km/s to 1.2 km/s, atomic hydrogen is transported equatorward, and auroral exospheric temperatures range from � 1200–1300 K to above 3000 K, depending on the magnitude of Joule heating. The equatorial temperature profiles from the JTGCM are compared with the measured temperature structure from the Galileo ASI data set. The best fit to the Galileo data implies that the major energy source for maintaining the equatorial temperatures is due to dynamical heating induced by the low-latitude convergence of the high-latitude-driven thermospheric circulation. Overall, the Jupiter thermosphere/ionosphere system is highly variable and is shown to be strongly dependent on magnetospheric coupling which regulates Joule heating.

Europa's surface composition and sputter‐produced ionosphere

The efficient sputtering and decomposition of Europas regolith by energetic charged particles produces an atmosphere representative of its surface composition. In addition to O2 and H2 from the decomposition of ice, we show that molecules representative of organics and salts will be present in ionic form at levels detectable using an ion mass spectrometer on an orbiting spacecraft. Such an instrument can also measure isotope ratios to determine surface age.

MAGNETOSPHERIC AND PLASMA SCIENCE WITH CASSINI-HUYGENS

Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres. These are an ‘induced’ magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturns ‘intrinsic’ magnetosphere, the magnetic cavity Saturns planetary magnetic field creates inside the solar wind flow. These two objects will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific questions concerning the interaction of these two magnetospheres with their environment.The flow of magnetospheric plasma around the obstacle, caused by Titans atmosphere/ionosphere, produces an elongated cavity and wake, which we call an ‘induced magnetosphere’. The Mach number characteristics of this interaction make it unique in the solar system. We first describe Titans ionosphere, which is the obstacle to the external plasma flow. We then study Titans induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic field of Titan.Saturns magnetosphere, which is dynamically and chemically coupled to all other components of Saturns environment in addition to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards, we first describe the region of the main rings and their connection to the low-latitude ionosphere. Next the icy satellites, which develop specific magnetospheric interactions, are imbedded in a relatively dense neutral gas cloud which also overlaps the spatial extent of the diffuse E ring. This region constitutes a very interesting case of direct and mutual coupling between dust, neutral gas and plasma populations. Beyond about twelve Saturn radii is the outer magnetosphere, where the dynamics is dominated by its coupling with the solar wind and a large hydrogen torus. It is a region of intense coupling between the magnetosphere and Saturns upper atmosphere, and the source of Saturns auroral emissions, including the kilometric radiation. For each of these regions we identify the key scientific questions and propose an investigation strategy to address them.Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible to address, and hopefully solve, many of these questions. While the CASSINI orbital tour gives access to most, if not all, of the regions that need to be explored, the unique capabilities of the MAPS instrument suite make it possible to define an efficient strategy in which in situ measurements and remote sensing observations complement each other.Saturns magnetosphere will be extensively studied from the microphysical to the global scale over the four years of the mission. All phases present in this unique environment — extended solid surfaces, dust and gas clouds, plasma and energetic particles — are coupled in an intricate way, very much as they are in planetary formation environments. This is one of the most interesting aspects of Magnetospheric and Plasma Science studies at Saturn. It provides us with a unique opportunity to conduct an in situ investigation of a dynamical system that is in some ways analogous to the dusty plasma environments in which planetary systems form.

First observation of Jupiter by XMM-Newton

We present the first X-ray observation of Jupiter by XMM-Newton. Images taken with the EPIC cameras show prominent emission, essentially all confined to the 0.2−2.0 keV band, from the planets auroral spots; their spectra can be modelled with a combination of unresolved emission lines of highly ionised oxygen (OVII and OVIII), and a pseudo-continuum which may also be due to the superposition of many weak lines. A 2.8� enhancement in the RGS spectrum at 21−22 A (∼0.57 keV) is consistent with an OVII identification. Our spectral analysis supports the hypothesis that Jupiters auroral em issions originate from the capture and acceleration of solar wind ions in the planets magnetosphere, followed by X-ray product ion by charge exchange. The X-ray flux of the North spot is modulat ed at Jupiters rotation period. We do not detect evidence fo r the∼45 min X-ray oscillations observed by Chandra more than two years earlier. Emission from the equatorial regions of the planets disk is also observed. Its spectrum is consistent w ith that of scattered solar X-rays.

The 10 October 1999 HIP 9369 occultation by the northern polar region of Jupiter: Ingress and egress lightcurves analysis

Abstract The occultation of bright star HIP9369 by the northern polar region of Jupiter was observed from four locations in North and South America, providing four data sets for ingress and egress. The inversion of the eight occultation lightcurves provides temperature profiles at different latitudes ranging from 55°N to 73.2°N. We estimate the errors on the profiles due to the uncertainties of the inversion method and compare the value of the temperature at the deepest level probed (∼ 50 μbar) with previous observations. The shape of the temperature gradient profile is found similar to previous investigations of planetary atmospheres with propagating and breaking gravity waves. We analyze the small scale structures in both lightcurves and temperature profiles using the continuous wavelet transform. The calculated power spectra of localized fluctuations in the temperature profiles show slopes close to −3 for all eight profiles. We also isolate and reconstruct the three-dimensional geometry of a single wave mode with vertical and horizontal wavelengths of respectively 3 and 70 km. The identified wave is consistent with the gravity wave regime, with a horizontal phase speed nearly parallel to the planetary meridian. Nevertheless, the dissipation of the corresponding wave in Jupiter’s stratosphere should preclude its detection at the observed levels and an acoustic wave cannot be ruled out.

Multispectral observations of Jupiter's Aurora

Remote sensing of Jupiters aurora from x-ray to radio wavelengths has revealed much about the nature of the jovian aurora and about the impact of ionosphere-magnetosphere coupling on the upper atmosphere of Jupiter. As indicated by the combination of x-ray and ultraviolet observations, both energetic heavy ions and electrons energized in the outer magnetosphere contribute to auroral excitation. Imaging with the Hubble Space Telescope in the ultraviolet and with the InfraRed Telescope Facility at infrared wavelengths shows several distinct regions of interaction: 1) a dusk sector where turbulent auroral patterns extend well into the polar cap; 2) a morning sector generally characterized by a single spatially confined auroral arc originating in the outer or middle magnetosphere of Jupiter; 3) diffuse emissions associated with the Io plasma - spectroscopy has provided important information about the thermal structure of Jupiters auroral atmosphere and the altitude distribution of auroral particle energy deposition, while Lyman alpha line profiles yield clues to the nature of thermospheric dynamical effects. Galileo observations at visible wavelengths on the nightside offer a new view of the jovian aurora with unprecedented spatial information. Infrared observations have added much to the understanding of thermal structure at all latitudes, the dynamics of the thermospheric wind system, and auroral morphology, and may hold the key to understanding the role of Joule heating in Jupiters thermosphere. ROSAT observations have revealed soft x-ray emissions from Jupiters lower latitudes as well as from the auroral zones, implying that energetic particle precipitation also occurs at low latitudes in regions magnetically linked to the inner radiation belts. In this review, multispectral observations of jovian auroral emissions are presented within a theoretical/modeling framework that is intended to provide some insight into magnetosphere-ionosphere coupling and its effects on the upper atmosphere.

N2 vibrational distribution in aurorae

Abstract The N 2 vibrational distribution is calculated for a specific IBC Class II aurora using as input, data obtained from coordinated rocket and satellite observations and currently accepted excitation and quenching rates. The results of the calculations indicate no significant vibrational enhancements for this specific aurora nor for “upper limit” estimates for more intense aurorae. We conclude from this study that if significantly larger concentrations of vibrationally excited N 2 molecules exist in the aurora, as recent rocket e.u.v. measurements suggest, current concepts of the sources and sinks of N 2 vibrational excitation will require significant revision.