Jupiter's ultraviolet polar auroral emissions

Conference (2009, September)

Not Available

Io UV footprint various spots: position and brightness variations

Conference (2009, July 27)

The Io UV footprint: Location, inter-spot distances and tail vertical extent

in Journal of Geophysical Research. Space Physics (2009), 114

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by ... [more ▼]

The Io footprint (IFP) consists of one or several spots observed in both jovian hemispheres and is related to the electromagnetic interaction between Io and the magnetosphere. These spots are followed by an auroral curtain, called the tail, extending more than 90° longitude in the direction of planetary rotation. We use recent Hubble Space Telescope images of Jupiter to analyze the location of the footprint spots and tail as a function of Io's location in the jovian magnetic field. We present here a new IFP reference contour---the locus of all possible IFP positions---with an unprecedented accuracy, especially in previously poorly covered sectors. We also demonstrate that the lead angle - the longitudinal shift between Io and the actual IFP position - is not a reliable quantity for validation of the interaction models. Instead, the evolution of the inter-spot distances appears to be a better diagnosis of the Io-Jupiter interaction. Moreover, we present observations of the tail vertical profiles as seen above the limb. The emission peak altitude is ~900 km and remains relatively constant with the distance from the main spot. The altitudinal extent of the vertical emission profiles is not compatible with precipitation of a mono-energetic electron population. The best fit is obtained for a kappa distribution with a characteristic energy of ~70 eV and a spectral index of 2.3. The broadness of the inferred electron energy spectrum gives insight into the physics of the electron acceleration mechanism at play above the IFP tail. [less ▲]

Equatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations

in Geophysical Research Letters (2009), 36

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes ... [more ▼]

We study the auroral emissions equatorward of the main oval based on Hubble Space Telescope (HST) observations of both Jovian hemispheres on September 20, 1997. On the same day, Galileo observed changes in the electron pitch angle distribution between the inner and middle magnetosphere (PAD boundary), indicative of electron diffusion. This region, magnetically maps to the equatorward diffuse emissions on both hemispheres. Whistler mode waves, observed simultaneously, can scatter electrons into the loss cone and lead to electron precipitation in the ionosphere. Based on simultaneous HST FUV and Galileo wave and electron data we test the conditions for electron scattering by whistler mode waves and derive the energy flux precipitated in the ionosphere. The comparison of the derived precipitation energy flux with the observed auroral brightness indicates that the energy contained in the PAD boundary can account for the auroral emissions. [less ▲]

Recent results from HST and ground-based observations of Saturn's aurora

Conference (2008, December 01)

Current observations of Saturn's aurora performed from Earth-orbit with HST and ground based instruments more than complement the in situ measurements obtained by the Cassini spacecraft. These remote ... [more ▼]

Current observations of Saturn's aurora performed from Earth-orbit with HST and ground based instruments more than complement the in situ measurements obtained by the Cassini spacecraft. These remote observations focus on two spectral windows revealing different facets of the same auroral phenomenon. The auroral photons captured in the ultraviolet bandwidth result from direct impact excitation of H and H2 by charged particles accelerated along magnetic field lines, while the thermal infrared emission involves additional steps in order to produce hot H3+ from the auroral energy. Each spectral window presents its own advantages. The high spatial and temporal resolution of the recent UV images obtained with HST make it possible to discriminate auroral sub-structures, such as short lived arcs and spots, and to map them into the magnetosphere where they can be associated with in situ observations. Infrared high resolution spectroscopy and emission-line imaging from ground observatories (IRTF, UKIRT) have more modest spatial resolution; however they recently pinned down emissions barely observed in the UV. Furthermore, they offer a direct measurement of the ion wind velocities in the auroral ionosphere. These ion flow patterns might then be used to untangle the origin of the auroral particles. The complementarity of observations obtained in the UV and IR bandwidths provides a powerful tool to study the auroral mechanisms in the Kronian magnetosphere and the atmospheric response to the auroral input. [less ▲]

Jupiter’s main auroral emission; local time and temporal variability

Conference (2008, September 23)

Jupiter's main auroral oval is associated with the ionosphere-magnetosphere coupling current system which is related to the breakdown of corotation in the middle magnetosphere. Its auroral footpath is ... [more ▼]

Jupiter's main auroral oval is associated with the ionosphere-magnetosphere coupling current system which is related to the breakdown of corotation in the middle magnetosphere. Its auroral footpath is usually represented as a smooth line closing around the pole. However, this simplistic view is misleading in many regards. We have constructed a new reference contour in the northern hemisphere (Figure 1), based on more than 1000 HST/UV images, which does not look like an oval and does not close around the pole. We use this reference contour to quantify the effects of temporal and local time variability of the magnetospheric plasma characteristics on the location of the main auroral emission. Beyond the orbit of Ganymede (15RJ), two key ingredients are expected to have a measurable influence on the instantaneous shape of the main emission contour: the azimuthal current flowing in the current sheet [1,2] and the corotation breakdown distance. The former affects the radial extent of the magnetic field lines, and the latter determines the radial location of the field aligned currents transmitting momentum from the planet to the lagging plasma. So far, models used to magnetically map the auroral main emission between the ionosphere and the equatorial plane assumed that these two parameters are constant and axisymmetric. However, in situ observations, mainly by Galileo, have revealed large local time asymmetries and temporal variations in the plasma flows and distribution. These variations have an impact on the azimuthal current and the distance at which the plasma angular velocity becomes significantly smaller than planetary rotation. We use a new magnetic field model [3], inherited from VIP4 and including a magnetic anomaly in the northern hemisphere, to simulate the effects of these asymmetries on the location of the main auroral emission, and interpret the large scattering of the corresponding HST data point. [less ▲]

Observational evidence of a localized magnetic anomaly near Jupiter’s North Pole

Conference (2008, April 18)

We have analyzed more than 1000 HST/ACS images of Jupiter’s ultraviolet auroral emission in the northern hemisphere. A systematic planet center finding algorithm made it possible to infer reliable and ... [more ▼]

We have analyzed more than 1000 HST/ACS images of Jupiter’s ultraviolet auroral emission in the northern hemisphere. A systematic planet center finding algorithm made it possible to infer reliable and consistent jovicentric location of the auroral footprints of Io, Europa and Ganymede. These footprints form reference contours which provide an absolute magnetic mapping from the ionosphere of Jupiter to the equatorial plane, independent of any magnetic field model. So far, the VIP4 magnetic field model is the most accurate in terms of fitting the auroral emissions. However, it cannot reproduce the distorted shape of the satellites UV footpaths in the “kink region” in the northern ionosphere between S3 longitudes 80 ̊-150 ̊. We show that the model is significantly improved by decreasing the VIP4 surface magnetic field in the kink region and by adding a localized dipolar perturbation field beneath the surface. [less ▲]

Jupiter’s diffuse auroral emissions - Comparison of HST and Galileo data

Conference (2008, April 18)

Based on an extensive HST FUV image database obtained between 1997 and 2007, we have studied the morphology and brightness of the equatorward diffuse auroral emissions in both Jovian hemispheres. The ... [more ▼]

Based on an extensive HST FUV image database obtained between 1997 and 2007, we have studied the morphology and brightness of the equatorward diffuse auroral emissions in both Jovian hemispheres. The emissions are wider and brighter on the dusk side than on the dawn and they often form multiple discrete arcs parallel to the main oval. What could be the origin of these equatorward diffuse emissions and their local time variations is still unclear. Galileo observations have shown changes in the electron pitch angle distributions between the inner and middle magnetosphere of Jupiter (10 to 17 RJ ) which could be associated with auroral emissions, without the need of field aligned currents. We derive the electron precipitation flux for the first time in a global scale, based on Galileo electron measurements between 10 and 17 RJ . We magnetically map this region in the ionosphere and compare the derived energy flux with the brightness of the diffuse emissions. We discuss the possibility that the energetic particle distribution in the middle magnetosphere could account for the multiple structured equatorward diffuse emissions and their local time variations. [less ▲]

Jupiter’s diffuse auroral emissions - Comparison of HST and Galileo data,

Conference (2008, April)

Observational evidence of a localized magnetic anomaly near Jupiter’s North Pole

Conference (2008, April)