References of "Saur, Joachim"
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See detailEvolution of the Io footprint brightness I: Far-UV observations
Bonfond, Bertrand ULg; Hess, Sébastien; Gérard, Jean-Claude ULg et al

in Planetary and Space Science (2013), 88

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the ... [more ▼]

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the brightness and precipitated power for each individual spot, using the image database gathered from 1997 to 2009 with the Hubble Space Telescope in the Far-UV domain. We show that the relative brightness of the spots varies with the System III longitude of Io. Moreover, our novel measurement method based on 3D simulations of the auroral features allows to derive the precipitated energy fluxes from images on which the emission region is observed at a slant angle. Peak values as high as 2 W/m² are observed for the main spot, probably triggering a localized and sudden heating of the atmosphere. Additionally, strong brightness differences are observed from one hemisphere to another. This result indicates that the location of Io in the plasma torus is not the only parameter to control the brightness, but that the magnetic field asymmetries also play a key role. Finally, we present new data confirming that significant variations of the spots' brightness on timescales of 2-4 minutes are ubiquitous, which suggests a relationship with intermittent double layers close to Jovian surface. [less ▲]

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See detailJUDE: A Far-UV Imager for JUICE
Grodent, Denis ULg; Bunce, Emma; Bannister, Nigel et al

Poster (2011, August 31)

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See detailHubble Space Telescope/Advanced Camera for Surveys Observations of Europa's Atmospheric Ultraviolet Emission at Eastern Elongation
Saur, Joachim; Feldman, Paul D; Roth, Lorenz et al

in Astrophysical Journal (2011), 738

We report results of a Hubble Space Telescope (HST) campaign with the Advanced Camera for Surveys to observe Europa at eastern elongation, i.e., Europa's leading side, on 2008 June 29. With five ... [more ▼]

We report results of a Hubble Space Telescope (HST) campaign with the Advanced Camera for Surveys to observe Europa at eastern elongation, i.e., Europa's leading side, on 2008 June 29. With five consecutive HST orbits, we constrain Europa's atmospheric O I 1304 Å and O I 1356 Å emissions using the prism PR130L. The total emissions of both oxygen multiplets range between 132 ± 14 and 226 ± 14 Rayleigh. An additional systematic error with values on the same order as the statistical errors may be due to uncertainties in modeling the reflected light from Europa's surface. The total emission also shows a clear dependence of Europa's position with respect to Jupiter's magnetospheric plasma sheet. We derive a lower limit for the O[SUB]2[/SUB] column density of 6 × 10[SUP]18[/SUP] m[SUP]-2[/SUP]. Previous observations of Europa's atmosphere with the Space Telescope Imaging Spectrograph in 1999 of Europa's trailing side show an enigmatic surplus of radiation on the anti-Jovian side within the disk of Europa. With emission from a radially symmetric atmosphere as a reference, we searched for an anti-Jovian versus sub-Jovian asymmetry with respect to the central meridian on the leading side and found none. Likewise, we searched for departures from a radially symmetric atmospheric emission and found an emission surplus centered around 90° west longitude, for which plausible mechanisms exist. Previous work about the possibility of plumes on Europa due to tidally driven shear heating found longitudes with strongest local strain rates which might be consistent with the longitudes of maximum UV emissions. Alternatively, asymmetries in Europa's UV emission can also be caused by inhomogeneous surface properties, an optically thick atmospheric contribution of atomic oxygen, and/or by Europa's complex plasma interaction with Jupiter's magnetosphere. [less ▲]

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See detailThe auroral footprint of Enceladus on Saturn
Pryor, Wayne R; Rymer, Abigail M; Mitchell, Donald G et al

in Nature (2011), 472

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between ... [more ▼]

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. [less ▲]

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See detailThe location and topology of electron beams in Io‘s wake
Jacobsen, Sven; Saur, Joachim; Neubauer, Friz et al

Conference (2009, April 22)

The Galileo spacecraft measured hot field aligned electron beams near Io during three flybys. We apply our 3D MHD model of the Io-Jupiter interaction to constrain the location and shape of field aligned ... [more ▼]

The Galileo spacecraft measured hot field aligned electron beams near Io during three flybys. We apply our 3D MHD model of the Io-Jupiter interaction to constrain the location and shape of field aligned electron beams for the individual flyby scenarios. Io continuously generates MHD waves by disturbing the Jovian magnetoplasma. Currents carried by Alfvén waves propagate predominantly along the magnetic field lines. The waves accelerate electrons as the number of charge carriers decreases on their way to Jupiter. These energetic electrons precipitate into the Jovian ionosphere, visible as prominent Io footprint emission in the Jovian aurora. On the other hand electrons have to be accelerated upward to form the beams measured by Galileo. Unlike the beam formation, the position and spatial structure of these beams has been poorly discussed. We adopt our 3D MHD model initial conditions to the individual flyby scenario and determine the spatial morphol- ogy of beams in Io’s orbital plane. We compare our findings to Galileo observations and find very good agreement. Moreover, we use our model to further investigate in detail a recent concept which involves cross-hemisphere electron beams to explain certain auroral features of the Io footprint emission such as a leading spot and secondary spots [Bonfond et al., 2008]. Our results indicate that besides geometrical properties, such as Io’s position in the torus, the incoming plasma density controls the travel path and topology of an electron beam. [less ▲]

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See detailThree-dimensional extension of the Io UV footprint emissions
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2008, September 23)

The Io UV footprint is an auroral feature observed close to the feet of the field lines passing through Io on both Jovian hemispheres. These light emissions are caused by the electromagnetic interaction ... [more ▼]

The Io UV footprint is an auroral feature observed close to the feet of the field lines passing through Io on both Jovian hemispheres. These light emissions are caused by the electromagnetic interaction between the satellite Io and the Jovian magnetosphere. For both the north and south poles, the Io footprint appears as a bright spot followed by a faint trailing tail and occasionally followed or preceded by secondary spots. The footprint morphology and the spots multiplicity have been found to vary with the location of Io in the plasma torus. [less ▲]

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See detailThe Io Footprint Morphology
Jacobsen, Sven; Saur, Joachim; Neubauer, F. M. et al

Conference (2008, September 23)

The innermost Galilean moon Io is embedded in a dense plasma torus. It disturbs the flow of the corotating torus plasma and generates MHD waves. Especially the Alfv ́ n e mode, which carries electric ... [more ▼]

The innermost Galilean moon Io is embedded in a dense plasma torus. It disturbs the flow of the corotating torus plasma and generates MHD waves. Especially the Alfv ́ n e mode, which carries electric currents along the magnetic field, is responsible for the famous Io footprint in the Jo- vian aurora. The Alfv ́ n waves are partly reflected at plasma e density gradients e.g. at the torus edges and form a compli- cated wave pattern. The footprint morphology in the Jovian aurora displays this pattern. Besides the main spot feature, a trailing wake extending over up to 100 degrees and occa- sionally occurring multiple spots indicating reflections have been identified. The intensity, the occurrence of multiple spots and the inter-spot distances have been found to vary strongly [1]. Io is moving up and down in the plasma torus confined to the centrifugal equator. It interacts with a dense plasma when located in the torus center and considerably thinner plasma at the torus flanks. The incoming plasma density controls the interaction strength and wave amplitude. This primar- ily leads to a relationship between the footprint brightness and Io’s centrifugal latitude [1]. However, it has also been shown that the reflection angle is strongly depending on the wave amplitude due to nonlinear effects [2]. This has an impact on the inter-spot distances. On the other hand this parameter is also directly affected when Io changes its posi- tion in the plasma torus. To deconvolve this system we present the results of our 3D MHD simulations showing the influence of Io’s centrifugal latitude and nonlinearities on the footprint morphology par- ticularly on the number of spots and inter-spot distances. We observe interference phenomena leading to locally en- hanced or reduced footprint brightness. We also discuss the recently observed leading spot feature [3]. [less ▲]

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See detailNew results on the UV Io footprint morphology and brightness
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Poster (2008, April 18)

The Io UV footprint is an auroral feature on Jupiter caused by the electromagnetic interaction between the satellite Io and the Jovian magnetosphere. The footprint morphology and the spots multiplicity ... [more ▼]

The Io UV footprint is an auroral feature on Jupiter caused by the electromagnetic interaction between the satellite Io and the Jovian magnetosphere. The footprint morphology and the spots multiplicity have been found to vary with the location of Io in the plasma torus. We show recent Hubble Space Telescope (HST) images that reveal a new feature in the footprint: a faint leading spot that appears upstream of the main spot in one hemisphere when Io is close to the opposite border of the torus. A possible interpretation relates the leading spots and one downward secondary spot to electron beams generated by downstream currents in the opposite hemisphere. We also present a 3D model of the Io footprint emissions in the 100 to 170 nm wavelength range. Comparisons between this model and the HST images enable us to study the actual size and shape of the different Io footprint features. It also allows to measure the footprint brightness on the new images with a better estimation of the geometric effects (e.g. limb brightening). The observations presented here provide critical constraints to the Io-plasma torus interaction modeling. [less ▲]

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See detailEvolution of the Io footprint morphology
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

Conference (2008, April)

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See detailUV Io footprint leading spot: A key feature for understanding the UV Io footprint multiplicity?
Bonfond, Bertrand ULg; Grodent, Denis ULg; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2008), 35(5),

The electromagnetic interaction between Io and the Jovian magnetosphere generates a UV auroral footprint in both Jovian hemispheres. Multiple spots were observed in the northern Jovian hemisphere when Io ... [more ▼]

The electromagnetic interaction between Io and the Jovian magnetosphere generates a UV auroral footprint in both Jovian hemispheres. Multiple spots were observed in the northern Jovian hemisphere when Io was in the northern part of the plasma torus and vice-versa for the South. Based on recent Hubble Space Telescope (HST) measurements, we report here the discovery of a UV leading spot, i.e., a faint emission located ahead of the main spot. The leading spot emerges at System III longitudes between 0 degrees and 100 degrees in the northern hemisphere and between 130 degrees and 300 degrees in the southern hemisphere, i. e., in one hemisphere when multiple spots are observed in the other hemisphere. We propose as one potential mechanism that electron beams observed near Io are related to the generation of the leading spot and the secondary spot in the opposite hemisphere. [less ▲]

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See detailUltraviolet Io footprint short timescale dynamics
Bonfond, Bertrand ULg; Gérard, Jean-Claude ULg; Grodent, Denis ULg et al

in Geophysical Research Letters (2007), 34(6),

The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple ultraviolet spots near the feet of the Io flux tube. Variations of spot numbers and brightness and of ... [more ▼]

The electromagnetic interaction between Io and Jupiter's magnetic field leads to single or multiple ultraviolet spots near the feet of the Io flux tube. Variations of spot numbers and brightness and of interspot distances have been observed to be linked to Io's position in its plasma torus. We have studied the evolution of the Io UV footprints with a time resolution of a few tens of seconds using the Space Telescope Imaging Spectrograph (STIS) in time-tag mode. We present evidence of systematic strong brightness variations of the main spots ( up to 50%) with a typical growth time of 1 minute. Additionally, unanticipated simultaneous fluctuations of both primary and secondary spots have also been found in the southern hemisphere. Our findings suggest that the footprint brightness is not only actively controlled by the plasma directly interacting with Io but also by the poorly constrained electron acceleration region between Io and Jupiter. [less ▲]

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