Auroral footprints; everywhere

Conference (2010, May 06)

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and ... [more ▼]

Jupiter’s moons Io, Europa and Ganymede are continuously interacting with the Jovian magnetic field and with the sheet of plasma flowing near its equatorial plane. The interaction between these moons and the Jovian magnetosphere causes strong Alfvénic perturbations which propagate along the magnetic field lines. On their way towards Jupiter’s polar regions, these perturbations accelerate charged particles which then interact with Jupiter’s ionosphere where they loose a fraction of their energy in the form of auroral emissions. Each of the three moons leaves an auroral footprint around the poles of Jupiter which departs from the bulk of the auroral emission. Their location is mainly controlled by the topology of the field lines and thus analysis of the auroral footprints provides information on the magnetic field itself. In that regard, the satellites auroral footpaths were used to highlight the presence of a strong magnetic anomaly in the northern hemisphere of Jupiter. Detailed inspection of the footprints’ brightness and morphology as a function of time reveals fundamental information on the interaction mechanisms near the moons, on the particles acceleration mechanisms as well as on the Jovian ionosphere. For example, it was suggested that the Io footprint actually consists of several spots resulting from successive steps in the perturbation propagation process. Another example is the finding of three different timescales in the variations of Ganymede’s footprint; each of them is pointing to a different part of the electromagnetic interaction between the moon’s mini-magnetosphere and the Jovian plasma. Several recent images of Saturn’s auroral regions obtained with Cassini/UVIS at high latitude show an obvious auroral spot at the predicted location of Enceladus’ footprint. This major finding demonstrates that the electromagnetic interaction between a moon and its parent planet is not unique to Jupiter but appears to be a common feature in planetary systems. [less ▲]

Venus OH nightglow distribution based on VIRTIS limb observations from Venus Express

in Geophysical Research Letters (2010), 37

The full set of VIRTIS‐M limb observations of the OH Venus nightglow has been analyzed to determine its characteristics. Based on 3328 limb profiles, we find that the mean peak intensity along the line of ... [more ▼]

The full set of VIRTIS‐M limb observations of the OH Venus nightglow has been analyzed to determine its characteristics. Based on 3328 limb profiles, we find that the mean peak intensity along the line of sight of the OH(deltaV = 1 sequence) is 0.35 MR and is located at 96.4 ± 5 km. The emission is highly variable and no dependence of the airglow layer altitude versus the antisolar angle is observed. The peak brightness appears to decrease away from the antisolar point even if the variability at a given location is very strong. Some correlation between the intensity of the OH and the O2(a1Delta) emissions is also observed, resumably because atomic oxygen is a common precursor to the formation of O2(a1Delta) and O3, whose reaction with H produces excited OH. Comparing our results with predictions from a photochemical model, a constant H flux does not match the simultaneous OH and O2 airglow observations. [less ▲]

Ultraviolet aurorae and dayglow in the upper atmospheres of terrestrial planets

in 38th COSPAR Scientific Assembly (2010)

Since its discovery in 2005 with the SPICAM spectrograph on board Mars Express, the Mars aurora has been further investigated. It is caused by sporadic soft electron precipitation whose signature is ... [more ▼]

Since its discovery in 2005 with the SPICAM spectrograph on board Mars Express, the Mars aurora has been further investigated. It is caused by sporadic soft electron precipitation whose signature is clearly observed in the FUV nightglow spectrum. The characteristics of the auroral electrons have been documented with parallel observations. Dayglow UV spectra have been collected with SPICAM over several seasons. The dependence of the intensity and peak altitude of the CO Cameron bands and CO2 + doublet emissions on latitude, local time and solar activity level have been investigated and compared with the results of a FUV Mars dayglow model. Far and Extreme ultraviolet spectra have been collected with the UVIS instrument during the flyby of Venus by Cassini, in a period a high solar activity. Their analysis shows the presence of OI, OII, NI, CI, CO and CO2 + emissions, some of them not previously identified in the Venus spectrum. The intensities will be compared with those observed with the HUT spectrograph during a period of low solar activity. The excitation processes of the observed features will be discussed. Scans of the intensity variation of several EUV bright emissions such as OII 83.4 nm, OI 98.9 nm and NI 120.0 nm multiplets across the sunlit disc will be compared with the calculations of a Venus dayglow model, including multiple scattering of optically thick transitions. [less ▲]

Saturn's secondary auroral ring

Conference (2010)

Not Available

The Venus OH Nightglow Distribution

Poster (2010)

The study shows that the OH emission is highly variable, ranging from less than 20 kR to about 2 MR. The peak brightness appears to decrease away from the antisolar point even if the variability at a ... [more ▼]

The study shows that the OH emission is highly variable, ranging from less than 20 kR to about 2 MR. The peak brightness appears to decrease away from the antisolar point even if the variability at a given location is very strong. By contrast, although the OH peak altitude also appears to be variable, it shows no dependence with the location on the nightside of Venus. Some correlation between simultaneous observations of the intensity of the OH and the O2(a1Δ) emissions has also been detected, presumably because atomic oxygen is a common precursor to the formation of O2(a1Δ) and O3, whose reaction with H produces excited OH. Anyway, it is important to keep in mind that horizontal transport plays an important role in the redistribution of photochemically produced species such as O, O3 and minor long-lived species and possibly explains some of the variability of the OH emission and its brightness relative to O2(a1 ). [less ▲]

How bright is the Io UV footprint?

Conference (2010)

The electro-magnetic interaction between Io and the Jovian magnetosphere generates a perturbation in the magnetospheric plasma which propagates along the magnetic field lines and creates auroral footprint ... [more ▼]

The electro-magnetic interaction between Io and the Jovian magnetosphere generates a perturbation in the magnetospheric plasma which propagates along the magnetic field lines and creates auroral footprint emissions in both hemispheres. Recent results showed that this footprint is formed of several spots and an extended tail. Each feature is suggested to correspond to a different step in the propagation of the perturbation and in the electron energization processes. The present study focuses on the variations of the spots' brightness at different timescales from minutes to years through the rotation period of Jupiter. It relies on FUV images acquired with the STIS and ACS instruments onboard the Hubble Space Telescope. Since the footprint is composed of several localized features, a good understanding of the emission region geometry is critical to derive the actual vertical brightness and thus the precipitated energy flux. We developed a 3D emission model in order to assess as precisely as possible the respective contribution of each individual feature and to correctly estimate the precipitating energy flux. As far as the brightness variations on timescales of minutes are concerned, we will present results from the high time resolution campaign executed during summer 2009. On timescale of several hours, we will show that the variation of the emitted power as a function of the location of Io in the plasma torus suggests that the Jovian surface magnetic field strength is an important controlling parameter. Finally, the measured precipitated power and particle fluxes will be discussed in comparison with recent simulations considering both Alfvén waves filamentation and electron acceleration when the Alfvén waves become inertial. [less ▲]

UVIS observations of the FUV OI and CO 4P Venus dayglow during the Cassini flyby

in Icarus (2010), 207

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of ... [more ▼]

We analyze FUV spatially-resolved dayglow spectra obtained at 0.37 nm resolution by the UVIS instrument during the Cassini flyby of Venus. We use a least-squares fit method to determine the brightness of the OI emissions at 130.4 and OI 135.6 nm, and of the bands of the CO fourth positive system which are dominated by fluorescence scattering. We compare the brightness observed along the UVIS foot track of the two OI multiplets with that deduced from a model of the excitation of these emissions by photoelectron impact on O atoms and resonance scattering of the solar 130.4 nm emission. The large optical thickness 130.4 nm emission is accounted for using a radiative transfer model. The airglow intensities are calculated along the foot track and found to agree with the observed 130.4 nm brightness within ˜10%. The modeled OI 135.6 nm brightness is also well reproduced by the model. The oxygen density profile of the VTS3 model is found to be consistent with the observations. We find that self-absorption of the (0, v″) bands of the fourth positive emission of CO is important and we derive a CO vertical column of about 6.4 × 10[SUP]15[/SUP] cm[SUP]‑2[/SUP] in close agreement with the value provided by the VTS3 empirical atmospheric model. [less ▲]

The distributions of the OH Meinel and O[SUB][/SUB](a[SUP]1[/SUP]Δ-X[SUP]3[/SUP]Σ) nightglow emissions in the Venus mesosphere based on VIRTIS observations

in Advances in Space Research (2010), 45

O[SUB][/SUB](a[SUP]1[/SUP]Δ) and recently discovered OH Meinel nightglow emissions have been observed at the limb with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS-M) instrument on board ... [more ▼]

O[SUB][/SUB](a[SUP]1[/SUP]Δ) and recently discovered OH Meinel nightglow emissions have been observed at the limb with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS-M) instrument on board the Venus Express satellite. Hydroxyl bands belonging to Δv=1 sequence between 2.60and3.14μm and to Δv=2 sequence at 1.40-1.46μm have been unambiguously identified. In this study, we analyze the statistical distribution of the Δv=1 OH Meinel band sequence and the a[SUP]1[/SUP]Δ[SUB]g[/SUB]-X[SUP]3[/SUP]Σ (0-0) band of the O[SUB][/SUB] Infrared Atmospheric bands at 1.27 μm. We also present an analysis of the correlation between the two emissions. From a statistical point of view, we find that the limb intensity of both emissions reach their maximum value near the antisolar point, while they are significantly dimmer in the vicinity of the terminator. The average altitude of the limb emissions peaks are 95.3 ± 3 km and 96 ± 2.7 km, respectively for the OH Δv=1 sequence and O[SUB][/SUB](a[SUP]1[/SUP]Δ) emissions. The average intensities are 0.41 ± 0.37 MR and 28 ± 22 MR, respectively, corresponding to a mean ratio of about 70. The altitude of the OH nightglow layer is closely related to that of the O[SUB][/SUB](a[SUP]1[/SUP]Δ) emission and some level of co-variation of the maximum intensity along the line of sight is observed. It is suggested that the global subsolar to antisolar circulation plays a key in the control of both airglows by carrying oxygen atoms from the day to the night side of the planet. The O atoms recombine to produce O[SUB][/SUB](a[SUP]1[/SUP]Δ) molecules and they also act as precursors of ozone whose reaction with H produces excited hydroxyl. [less ▲]

Variation of Saturn's UV aurora with SKR phase

in Geophysical Research Letters (2010), 37

It is well known that a wide range of kronian magnetospheric phenomena, including the Saturn kilometric radiation (SKR), exhibit oscillations near the planetary rotation period. However, although the SKR ... [more ▼]

It is well known that a wide range of kronian magnetospheric phenomena, including the Saturn kilometric radiation (SKR), exhibit oscillations near the planetary rotation period. However, although the SKR is believed to be generated by unstable auroral electrons, no connection has been established to date between diurnal SKR modulations and UV auroral power. We use an empirical SKR phase determined from Cassini observations to order the 'quiet time' total emitted UV auroral power as observed by the Hubble Space Telescope in programs during the interval 2005-2009. Our results indicate that both the northern and southern UV powers are dependent on SKR phase, varying diurnally by factors of similar to 3. We also show that the UV variation originates principally from the morning half of the oval, consistent with previous observations of the SKR sources. Citation: Nichols, J. D., B. Cecconi, J. T. Clarke, S. W. H. Cowley, J.-C. Gerard, A. Grocott, D. Grodent, L. Lamy, and P. Zarka (2010), Variation of Saturn's UV aurora with SKR phase, Geophys. Res. Lett., 37, L15102, doi: 10.1029/2010GL044057. [less ▲]

On the origin of Saturn's outer auroral emission

in Journal of Geophysical Research (Space Physics) (2010), 115

Ultraviolet Hubble Space Telescope images reveal a faint but distinct auroral emission equatorward of the main ring of emission of Saturn's southern polar region. This outer auroral emission is only ... [more ▼]

Ultraviolet Hubble Space Telescope images reveal a faint but distinct auroral emission equatorward of the main ring of emission of Saturn's southern polar region. This outer auroral emission is only visible near the nightside limb for the strongly tilted viewing geometry achieved in January 2004. We model the limb-brightening amplification of this emission, and we show that the observations are compatible with an ∼7° wide emission ring approximately centered on the 67°S parallel. The 1.7 kR brightness of this emission requires an injected electron energy flux of ∼0.3 mW m[SUP]‑2[/SUP]. The outer auroral emission maps to a region of the equatorial plane between 4 and 11 R[SUB]S[/SUB]. We suggest that a population of suprathermal electrons observed by Cassini can provide more than the required energy flux without the need for field-aligned acceleration. This auroral UV emission may also be associated with energetic neutral oxygen and hydrogen atoms originating from the energetic protons and O[SUP]+[/SUP] of magnetosphere and/or with a secondary infrared auroral oval. [less ▲]