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We present in this Keck AO paper the first global high angular resolution observations of Io in three broadband near-infrared filters: Kc (2.3 mu m), Lp (3.8 mu m), and Ms (4.7 mu m). The Keck AO observations are composed of 13 data sets taken during short time intervals spanning 10 nights in December, 2001. The MISTRAL deconvolution process, which is specifically aimed for planetary images, was applied to each image. The spatial resolution achieved with those ground-based observations is 150, 240, and 300 km in the Kc, Lp, and Ms band, respectively, making them similar in quality to most of the distant observations of the Galileo/NIMS instrument. Eleven images per filter were selected and stitched together after being deprojected to build a cylindrical map of the entire surface of the satellite. In Kc-band, surface albedc, features, such as paterae (R > 60 km) are easily identifiable. The Babbar region is characterized by extremely low albedo at 2.2 mu m, and shows an absorption band at 0.9 mu m in Galileo/SSI data. These suggest that this region is covered by dark silicate deposits, possibly made of orthopyroxene. In the Lp-Ms (3-5 mu m) bands, the thermal emission from active centers is easily identified. We detected 26 hot spots in both broadband filters over the entire surface of the minor planet; two have never been seen active before, nine more are seen in the Ms band. We focused our study on the hot spots detected in both broadband filters. Using the measurements of their brightness, we derived the temperature and area covered by 100 brightness measurements. Loki displayed a relatively quiescent activity. Dazhbog, a new eruption detected by Galileo/NIMS in August 2001, is a major feature in our survey. We also point out the fading of Tvashtar volcanic activity after more than two years of energetic activity, and the presence of a hot, but small, active center at the location of Surt, possibly a remnant of its exceptional eruption detected in February 2001. Two new active centers, labeled F and V on our data, are detected. Using the best temperature and the surface area derived from the L and M band intensities, we calculated the thermal output of each active center. The most energetic hot spots are Loki and Dazhbog, representing respectively 36 and 19% of the total output calculated from a temperature fit of all hot spots (20.6 x 10(12) W). Based on the temperature derived from hot spots (similar to 400 K), our measurement can unambiguously identify the contribution to the heat flux from the silicate portion of the surface. Because the entire surface was observed, no extrapolation was required to calculate that flux. It is also important to note that we measured the brightness of the individual hot spots when they were located close to the Central Meridian. This minimizes the line-of-sight effect which does not follow strictly a classical cosine law. Finally, we argue that despite the widespread volcanic activity detected, Io was relatively quiescent in December 2001, with a minimum mean total output of 0.4-1.2 W m(-2). This output is at least a factor of two lower than those inferred from observations made at longer wavelengths and at different epochs. (c) 2005 Elsevier Inc. All rights reserved.

The ten small inner moons of Uranus, discovered in 1986, have so far only been studied from space (Voyager 2, HST). The orbital elements derived from the observations indicate very weakly eccentric orbits for all of them but one (Ophelia). We present here the first ground-based astrometric observations of Puck, performed using an Adaptive Optics system. The long observing sequences permitted by ground-based facilities at ESO-La Silla, Chile (64.S-0289) revealed an eccentricity 100 times larger than previously believed. Such a disagreement with the actual theory may arise from the reduction itself based on the bright moons of Uranus, considered until now as precise astrometric references. To cite this article: P. Descamps et al., C. R. Physique 3 (2002) 121–128

Following the recent detection of an auroral signal on Uranus (Lamy et al. [2012]. Geophys. Res. Lett. 39, 7105) during HST/STIS observation performed in November 2011, we analyzed the associated HST/STIS FUV spectral images obtained in 2011 and 2012. Our purpose was to extract any possible H2 emission produced in the upper atmosphere of the planet. To interpret these data, we adapted a version of the kinetic Trans* code to the Uranian case. This code simulates the H2 emissions created by energetic particle precipitations in the upper atmosphere. The signal measured in the 1330-1700 A range, of around 1.8 kR, is composed mostly of reflected sunlight with a small contribution from upper atmospheric emissions. For most spectra, we found no evidence of particle precipitation, indicating a precipitation flux smaller than 0.01 erg cm-2 s-1. For the spectrum of 29 November 2011 however, when an auroral spot was positively detected, we additionally identified a small contribution of H2 emission which requires a precipitating energy flux up to 0.05 erg cm-2 s-1. This study also establishes that the Hubble Space Telescope (HST) can be used to monitor the aurorae on Uranus in its image and spectral modes, and to estimate the associated precipitated energy flux, provided a very careful data processing is applied. (Less)

Two opposite hemispheres of Io were observed on October 20 and 21, 1996, through an L′ broadband filter, using the high-resolution capability of the Adaptive Optics (AO) system implemented on the ESO 3.6-m telescope at La Silla, Chile. These observations, performed at thermal wavelengths when Io is in daylight, have been carefully processed to improve the sharpness of the initial, diffraction-limited, images. The myopic deconvolution process used ( idac ) achieved an angular resolution estimated to be 0.15 arcsec, corresponding to a spatial resolution of ∼570 km on Io's disc at the time of the observations. The final images show a number of bright features which have been compared with the Galileo/NIMS data, the only data set with a comparable resolution available for the anti-Jovian side of the satellite as well as its Jupiter-facing side. Our maps of the hot spot distribution are quite consistent with the Galileo data. The Jupiter-facing side is dominated by emission from Loki, which accounts for ∼25% of the total hot spot emission from that side (and 45% of that we were able to resolve and identify), although Loki was in a phase of decreasing activity (but not yet quiescent), as derived from ground-based monitoring observations. A few more hot sources are detected, including Pele–Pillan. The other hemisphere is characterized by a large number of moderately bright hot spots which are distributed around Bosphorus Regio. These preliminary observations fully demonstrate the capabilities of an AO system coupled with a thermal camera to monitor the volcanic activity of Io, in terms of morphology as well as thermal output. These monitoring capabilities will become especially important when the Galileo mission ends.

We present ground-based observations of the jovian ionospheric H+3 emission at 4 micrometers, using the CSHELL facility long-slit spectrograph at the NASA Infrared Telescope Facility (IRTF) in Hawaii. The data were obtained during four consecutive nights from July 13 to July 16, 1996. The 30-arcsec length slit of the spectrograph was aligned with the jovian CML, in order to get high-spatial, high-spectral resolution latitudinal profiles of the jovian H+3 emission. A self-consistent multi-emission-component (MEC) model, developed for the analysis of these latitudinal profiles, simulates the emission from the vertical distribution of the ionization components known to produce H+3. We initially identify these as solar-EUV photo-ionization, auroral oval precipitation, and diffuse auroral precipitation. A fourth component, mid-to-low (MTL)-latitude ionization is derived, and then fitted. InfraRed H+3 auroral ovals follow closely the UV ovals as observed with the HST instruments WFPC2 and FOC. Our model shows that the auroral production rate is generally between a few and a few tens of times the EUV rate. The MTL component production rate is 1 to 40% of the auroral rate in the north, and 2 to 16% in the south. Input and output energies are scaled to solar EUV values. We assume an EUV insolation of 60 μW/m2, equivalent to a total jovian EUV insolation of 1012W. Scaled to the EUV input, planetwide integration of the components of our model produces the total hemispheric energy inputs associated with the aurora, the diffuse emission, and the MTL emission. The results are 1.22(±.25)×1012W, 0.37(±.15)×1012W, and 0.65(±.32)×1012W, respectively, for the north and 1.15(±.30)×1012W, 0.21(±.10)×1012W, and 0.64 (±.32)×1012W for the south, respectively. We discusss the limitations of our scaling process, introducing the notion of emission efficiency with respect to a nominal 1000K/LTE H+3 emitter. The overall auroral emission is approximately 43 (+107, −23)% of that measured in 1993. Our results show that H+3 controls the energy balance of the auroral regions above the homopause, as well as the equatorial regions.

Simultaneous observations of Jupiter in the 3.5–4 μm range with a camera on the NASA IRTF and a Fourier transform spectrometer on the CFHT are analyzed to retrieve the spectral, spatial, and temporal characteristics of the polar emissions. At 3.50μm, a uniform planetary background is observed, with a spatial extent similar to the polar haze observed at 8900 A and 2 μm. After subtraction of this continuum, pure H3+ emission appears in the corrected images at 3.53 μm. Maximum emission is observed in a limited latitudinal range, between 60° and 70° latitude, both north and south. The longitudinal distribution of emission exhibits strong maxima, which are called “auroral spots”, from which most of the emission originates. In the north, two spots are observed, separated by about 60°, with a narrow bridge between them, forming a weaker “arc” of emission, centered at about 180° of System III longitude. At longitudes outside this arc, the emission is weaker by at least a factor of 8. The spots are roughly fixed in System III longitude. In the south, the description is more complex. The emission is also mostly confined to auroral spots, but the longitude of the spots is found to vary temporally. Two spots are observed in a time series covering half a Jovian rotation. Compared to the north, the emission is mostly confined to a broader longitude range, −20° ≤ λIII ≤ 140°. Within this range, a narrow emission peak is observed to shift with time toward greater longitude, at a rate slightly smaller than the Jovian rotation rate. It is observed at almost constant local time, about 20° to 35° eastward of central meridian. The intensity of the spot varies continuously, with an absolute maximum for longitudes 60° ≤ λIII ≤ 90°. The spatial characteristics of the H3+ emission are compared to the Voyager UVS Ly α observations, to thermal infrared auroral observations, and to recent models of auroral emissions. The pairs of northern hot spot peaks are accurately located on the polar edge of the “UVS auroral oval.” The southern hot spot peaks are located, within the error bars, on the theoretical O4 L = 8 magnetic footprint. In System III longitude, the north peaks bracket the average locations of the UV peak and of the CH4 IR hot spot. In the south, the apparent motion of the spot, as described above, can be interpreted as the convolution of an emission peak fixed in longitude at λIII ≈ 80°, close to the UV emission peak, with a modulation that is fixed in local time and maximum at about 30° from the central meridian. Comparison with the models suggests that within a pair of spots, each one could be related to different precipitating particles: electrons and ions.

International audience; The Lyman beta dayglow of Jupiter provides an important source of information about its atmosphere. The H Lyman beta and the H26-0 P(1) line of the Lyman system overlap, resulting in a coupling effect between these two lines. In this paper, we evaluate the effect of this overlapping via radiative transfer modelling and show its effect both on the integrated intensity and the line profile. The intensity increases at about 1025 Å at the centre of the disc, tends to slightly decrease at the limb, and creates an asymmetry in the profile. This asymmetry is also present in the jovian H-Lyman alpha bulge region.

International audience; After having used an analytical expression in the form of a power series expansion to calculate the interelectrode electrostatic field in the general case of a toroidal electrostatic analyzer, we derive approximate analytical expressions for the most interesting response functions (geometrical factor, angular aperture, energy resolution, etc.). Results of a study of the dependence of these quantities with respect to the geometrical parameters of the analyzers are given in the form of grids of curves. By using such grids one is able to determine the optimal parameters to obtain any particular solution. Examples of such a choise are given in the case of measurements of low energy particles in space (10 eV to 50 keV).

On présente une méthode numérique de détermination des caractéristiques d'analyseurs électrostatiques de particules, valable dans le cas général d'électrodes toriques. Le champ électrostatique est exprimé sous forme d'un développement limité en fonction de coordonnées réduites, définissant la position d'un point par rapport à l'équipotentielle moyenne. On évalue les coefficients de ce développement jusqu'à un ordre donné quelconque, et la trajectoire d'une particule est déterminée par intégration numérique des équations du mouvement. On aboutit, par exploration des différents cas d'incidence, aux grandeurs caractéristiques de l'analyseur. Les résultats sont comparés avec ceux obtenus au moyen d'une simulation en cuve rhéographique. On présente deux exemples concrets d'utilisation du programme numérique mis au point, exemples qui répondent à des problèmes de mesure en milieu spatial : analyseur à grands pouvoirs de résolution en énergie et en angle, analyseur à grand domaine d'entrée et large bande passante en énergie. La forme torique permet d'élargir de manière très appréciable le cadre des performances obtenues à l'aide d'analyseurs de formes classiques, cylindriques ou sphériques.

We study three models of electrostatic mirror analyzers and show that these kinds of instruments are inadequate to analyze energetic particles because they require too high retarding voltages compared to the mean energy of the particles analyzed.

International audience; The possible role of ULF waves observed in the Io torus in the generation of Jovian aurorae is investigated. Auroral emissions have been observed, not only at high latitude, but also at the footprint of magnetic field lines connected to the Io torus in a limited longitudinal range around 150°. As Ulysses passed by Jupiter, it explored the Io torus in latitude and longitude, allowing to test a possible localization of the waves on field lines mapping down into the aurora. A maximum intensity of the waves is observed in the high latitude part of the torus around the longitude where the aurorae were observed. Another maximum is also observed at the magnetic equator. The propagation mode of the waves is discussed and their amplitude is compared to the values necessary for scattering ions, showing that the ULF waves could possibly be at the origin of the aurorae.

We describe a rocket‐borne instrument for measurement of the low energy electron and proton distribution function in the magnetosphere. It consists of an optimized programmable electrostatic toroidal analyzer as an energy selector, coupled with an electron multiplier as a particle detector, and of the associated electronics. Much attention has been paid to the experimental calibration of the instrument which gives us some understanding of the real behavior of the detector and the way it influences the analyzer properties.