References of "Badman, S. V"
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See detailCassini nightside observations of the oscillatory motion of Saturn's northern auroral oval
Bunce, E. J.; Grodent, Denis ULg; Jinks, S. L. et al

in Journal of Geophysical Research. Space Physics (2014), 119

recent years we have benefitted greatly from the first in-orbit multi-wavelength images of Saturn's polar atmosphere from the Cassini spacecraft. Specifically, images obtained from the Cassini UltraViolet ... [more ▼]

recent years we have benefitted greatly from the first in-orbit multi-wavelength images of Saturn's polar atmosphere from the Cassini spacecraft. Specifically, images obtained from the Cassini UltraViolet Imaging Spectrograph (UVIS) provide an excellent view of the planet's auroral emissions, which in turn give an account of the large-scale magnetosphere-ionosphere coupling and dynamics within the system. However, obtaining near-simultaneous views of the auroral regions with in situ measurements of magnetic field and plasma populations at high latitudes is more difficult to routinely achieve. Here we present an unusual case, during Revolution 99 in January 2009, where UVIS observes the entire northern UV auroral oval during a 2 h interval while Cassini traverses the magnetic flux tubes connecting to the auroral regions near 21 LT, sampling the related magnetic field, particle, and radio and plasma wave signatures. The motion of the auroral oval evident from the UVIS images requires a careful interpretation of the associated latitudinally "oscillating" magnetic field and auroral field-aligned current signatures, whereas previous interpretations have assumed a static current system. Concurrent observations of the auroral hiss (typically generated in regions of downward directed field-aligned current) support this revised interpretation of an oscillating current system. The nature of the motion of the auroral oval evident in the UVIS image sequence, and the simultaneous measured motion of the field-aligned currents (and related plasma boundary) in this interval, is shown to be related to the northern hemisphere magnetosphere oscillation phase. This is in agreement with previous observations of the auroral oval oscillatory motion. [less ▲]

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See detailDynamic auroral storms on Saturn as observed by the Hubble Space Telescope
Nichols, J. D.; Badman, S. V.; Baines, K. H. et al

in Geophysical Research Letters (2014), 41

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission ... [more ▼]

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ˜330% rigid corotation from near ˜01 h LT toward ˜08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current. [less ▲]

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See detailThe science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets
Arridge, C. S.; Achilleos, N.; Agarwal, J. et al

in Planetary and Space Science (2014), (0), -

Abstract Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun's planetary system. They can be subdivided into the Ice ... [more ▼]

Abstract Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun's planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus’ atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency's call for science themes for its large-class mission programme in 2013. [less ▲]

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See detailMultispectral simultaneous diagnosis of Saturn's aurorae throughout a planetary rotation
Lamy, L.; Prangé, R.; Pryor, W. et al

in Journal of Geophysical Research. Space Physics (2013), 118

From 27 to 28 January 2009, the Cassini spacecraft remotely acquired combined observations of Saturn's southern aurorae at radio, ultraviolet, and infrared wavelengths, while monitoring ion injections in ... [more ▼]

From 27 to 28 January 2009, the Cassini spacecraft remotely acquired combined observations of Saturn's southern aurorae at radio, ultraviolet, and infrared wavelengths, while monitoring ion injections in the middle magnetosphere from energetic neutral atoms. Simultaneous measurements included the sampling of a full planetary rotation, a relevant timescale to investigate auroral emissions driven by processes internal to the magnetosphere. In addition, this interval coincidentally matched a powerful substorm-like event in the magnetotail, which induced an overall dawnside intensification of the magnetospheric and auroral activity. We comparatively analyze this unique set of measurements to reach a comprehensive view of kronian auroral processes over the investigated timescale. We identify three source regions for the atmospheric aurorae, including a main oval associated with the bulk of Saturn Kilometric Radiation (SKR), together with polar and equatorward emissions. These observations reveal the coexistence of corotational and subcorototational dynamics of emissions associated with the main auroral oval. Precisely, we show that the atmospheric main oval hosts short-lived subcorotating isolated features together with a bright, longitudinally extended, corotating region locked at the southern SKR phase. We assign the substorm-like event to a regular, internally driven, nightside ion injection possibly triggered by a plasmoid ejection. We also investigate the total auroral energy budget, from the power input to the atmosphere, characterized by precipitating electrons up to 20 keV, to its dissipation through the various radiating processes. Finally, through simulations, we confirm the search-light nature of the SKR rotational modulation and we show that SKR arcs relate to isolated auroral spots. We characterize which radio sources are visible from the spacecraft and we estimate the fraction of visible southern power to a few percent. The resulting findings are discussed in the frame of pending questions as the persistence of a corotating field-aligned current system within a subcorotating magnetospheric cold plasma, the occurrence of plasmoid activity, and the comparison of auroral fluxes radiated at different wavelengths. [less ▲]

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See detailBursty magnetic reconnection at Saturn's magnetosphere
Badman, S. V.; Masters, A.; Hasegawa, H. et al

in Geophysical Research Letters (2013)

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See detailAuroral counterpart of magnetic field dipolarizations in Saturn's tail
Jackman, C. M.; Achilleos, N.; Bunce, E. J. et al

in American Geophysical Union, Fall Meeting 2011, abstract #SM14A-07 (2011, December 01)

Following magnetic reconnection in a planetary magnetotail, newly closed field lines can be rapidly accelerated back towards the planet, becoming "dipolarized" in the process. At Saturn, dipolarizations ... [more ▼]

Following magnetic reconnection in a planetary magnetotail, newly closed field lines can be rapidly accelerated back towards the planet, becoming "dipolarized" in the process. At Saturn, dipolarizations can be initially identified from the magnetometer data by looking for a southward turning of the magnetic field, indicating the transition from a radially stretched configuration to a more dipolar field topology. The highly stretched geometry of the kronian magnetotail lobes gives rise to a tail current which flows eastward (dusk to dawn) in the near equatorial plane across the centre of the tail. During reconnection and associated dipolarization of the field, the inner edge of this tail current can be diverted through the ionosphere, in a situation analogous to the substorm current wedge picture at Earth [McPherron et al. 1973]. We present a picture of the current circuit arising from this tail reconfiguration, and outline the equations which govern the field-current relationship. We show a number of examples of dipolarizations as identified in the Cassini magnetometer data and use this formalism to calculate limits for the ionospheric current density that would arise for these examples. In addition to the magnetometer data, we also present data from the Cassini VIMS and UVIS instruments which have observed small 'spots' of auroral emission lying near the main oval - features thought to be associated with dipolarizations in the tail. We compare the auroral intensities as predicted from our calculation with the observed spot sizes and intensities. [less ▲]

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See detailSaturn's aurora as viewed by Cassini VIMS
Melin, H.; Stallard, T.; Badman, S. V. et al

Conference (2011, December 01)

The stunning views of the kronian aurora captured by the Visual and Infrared Imaging Spectrograph (VIMS) onboard the Cassini spacecraft continues to provide crucial observations of the fervent interaction ... [more ▼]

The stunning views of the kronian aurora captured by the Visual and Infrared Imaging Spectrograph (VIMS) onboard the Cassini spacecraft continues to provide crucial observations of the fervent interaction between the upper atmosphere and the magnetosphere of Saturn. Here, we present recent findings of VIMS auroral research, which includes both statistical studies and case studies of auroral events and morphology. In addition to stand-alone observations, there is a small subset of VIMS observations during which UVIS was also acquiring data. These observations enable the comparison between observations of H, H2 in the ultraviolet and H3+ in the infrared that are both spatially overlapping and temporally simultaneous. Whilst emission tends to coincide for these three species on the main oval, there are significant differences both pole-ward and equator-ward, such that observations of H and H2 is generally a poor proxy for emissions of H3+. VIMS is sensitive to infrared thermal emission from the H3+ molecule, which is formed very efficiently via the ionisation of H2. Therefore, the morphology of H3+ emission becomes a tracer of energy injected into the upper atmosphere - the most striking of which is auroral particle precipitation. [less ▲]

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See detailSimultaneous Cassini VIMS and UVIS observations of Saturn's southern aurora
Melin, H.; Stallard, T.; Miller, S. et al

in EPSC-DPS Joint Meeting 2011 (2011, October 01)

Here, temporally simultaneous and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. The pointing is fixed at a constant local time of 04:55, covering ... [more ▼]

Here, temporally simultaneous and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. The pointing is fixed at a constant local time of 04:55, covering latitudes between 64°S and 82°S and longitudes between 127° and 186°. The spatial resolution is high, with 1 mrad covering ˜300 km, such that only a small part of the pre-dawn aurora is observed. Ultraviolet auroral H and H2 emissions from UVIS are compared to infrared H+3 emission from VIMS. The auroral emission is structured into three arcs - H, H2 and H+3 are morphologically identical in the bright main auroral oval (˜73°S), but there is an equatorward arc that is seen predominantly in H (˜70°S), and a poleward arc (˜74°S) that is seen mainly in H2 and H+3 . These observations indicate that, for the main auroral oval, the UV emission is a good proxy for the infrared H+3 morphology (and vice versa), but for emission either poleward or equatorward this is no longer true. Hence, given the highly dynamic nature of the aurora of Saturn, simultaneous UV/IR observations are crucial for completing the picture of how the atmosphere interacts with the magnetosphere. [less ▲]

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See detailSimultaneous Cassini VIMS and UVIS observations of Saturn's southern aurora: Comparing emissions from H, H2 and H3+ at a high spatial resolution
Melin, H.; Stallard, T.; Miller, S. et al

in Geophysical Research Letters (2011), 38

Here, for the first time, temporally coincident and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. Ultraviolet auroral H and H[SUB]2[/SUB] emissions ... [more ▼]

Here, for the first time, temporally coincident and spatially overlapping Cassini VIMS and UVIS observations of Saturn's southern aurora are presented. Ultraviolet auroral H and H[SUB]2[/SUB] emissions from UVIS are compared to infrared H[SUB]3[/SUB][SUP]+[/SUP] emission from VIMS. The auroral emission is structured into three arcs - H, H[SUB]2[/SUB] and H[SUB]3[/SUB][SUP]+[/SUP] are morphologically identical in the bright main auroral oval (˜73°S), but there is an equatorward arc that is seen predominantly in H (˜70°S), and a poleward arc (˜74°S) that is seen mainly in H[SUB]2[/SUB] and H[SUB]3[/SUB][SUP]+[/SUP]. These observations indicate that, for the main auroral oval, UV emission is a good proxy for the infrared H[SUB]3[/SUB][SUP]+[/SUP] morphology (and vice versa), but for emission either poleward or equatorward this is no longer true. Hence, simultaneous UV/IR observations are crucial for completing the picture of how the atmosphere interacts with the magnetosphere. [less ▲]

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See detailEvolution of Saturn's Bright Polar Aurora
Stallard, T.; Grodent, Denis ULg; Badman, S. V. et al

Conference (2009)

Observations of Saturn's infrared aurorae have shown that in addition to the main auroral oval, which is believed to be associated with the solar wind, there are significant polar emissions. Ground-based ... [more ▼]

Observations of Saturn's infrared aurorae have shown that in addition to the main auroral oval, which is believed to be associated with the solar wind, there are significant polar emissions. Ground-based infrared observations of Saturn have been able to show that there is a general level of raised emission across the entire polar region, in a similar way to that seen at Jupiter. However, with direct observations of the aurora made from orbit around Saturn by the Cassini-VIMS instrument, this aurora was shown to be more than a relative generalised brightening in the infrared. Instead, a unique auroral feature was observed to occur, appearing as a large region of bright polar emission, positioned poleward of 82 degrees latitude. This Bright Polar Aurora emission is significantly different from the recently observed subrotating Q-branch auroral emission seen in both the ultraviolet and infrared, as it is separated from the main auroral oval by a region of low emission. This effectively produces a cap of bright aurora inside the main auroral oval, surrounded by a dark ring that separates the two aurorae. Here, we take a more detailed look at this cap of emission and examine the way the auroral feature develops with time. Bright Polar Aurora emission has been observed in two separate VIMS images. A more detailed analysis of the polar emission shows that each of these images in fact differs in structure; the first has auroral emission across the whole polar cap >82 degrees, but within the second the emission is concentrated on the dusk side. While the dramatic in-filling of the polar cap is not seen within any UV observations, the Hubble Space Telescope has observed transitory duskward auroral features within the polar cap, in a similar location to the duskward feature seen in the infrared. Using ground-based infrared observations, which allow a Bright Polar Aurora event to be broken into shorter timescale steps, it is possible analyse the progression of the infrared auroral emission with time, connecting the morphology seen within the two VIMS images with those in the ultraviolet. [less ▲]

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See detailSaturn's equinoctial auroras
Nichols, J. D.; Badman, S. V.; Bunce, E. J. et al

in Geophysical Research Letters (2009), 36

We present the first images of Saturn's conjugate equinoctial auroras, obtained in early 2009 using the Hubble Space Telescope. We show that the radius of the northern auroral oval is similar to 1.5 ... [more ▼]

We present the first images of Saturn's conjugate equinoctial auroras, obtained in early 2009 using the Hubble Space Telescope. We show that the radius of the northern auroral oval is similar to 1.5 degrees smaller than the southern, indicating that Saturn's polar ionospheric magnetic field, measured for the first time in the ionosphere, is similar to 17% larger in the north than the south. Despite this, the total emitted UV power is on average similar to 17% larger in the north than the south, suggesting that field-aligned currents (FACs) are responsible for the emission. Finally, we show that individual auroral features can exhibit distinct hemispheric asymmetries. These observations will provide important context for Cassini observations as Saturn moves from southern to northern summer. Citation: Nichols, J. D., et al. (2009), Saturn's equinoctial auroras, Geophys. Res. Lett., 36, L24102, doi: 10.1029/2009GL041491. [less ▲]

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See detailA statistical analysis of the location and width of Saturn's aurora, and implications for magnetospheric dynamics
Badman, S. V.; Cowley, S. W. H.; Gérard, Jean-Claude ULg et al

Conference (2006, September)

We present the results of a statistical analysis of the location of commonly-occurring auroral features in Saturn's southern polar ionosphere. Using a magnetospheric model, modified for Saturn from a data ... [more ▼]

We present the results of a statistical analysis of the location of commonly-occurring auroral features in Saturn's southern polar ionosphere. Using a magnetospheric model, modified for Saturn from a data-based terrestrial model (Tsyganenko, 1996), we estimate the region in the equatorial plane of the outer magnetosphere that maps to the observed aurora. We then discuss the possible magnetospheric processes that may cause these auroral emissions. [less ▲]

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See detailOpen Flux Estimates and Reconnection Rates in Saturn's Magnetosphere, Derived Using HST and Cassini Data
Badman, S. V.; Bunce, E. J.; Clarke, J. T. et al

Conference (2005, December 01)

During January 2004, a sequence of 68 UV images of Saturn's southern aurora was obtained by the Hubble Space Telescope (HST), coordinated with measurements of the upstream interplanetary conditions made ... [more ▼]

During January 2004, a sequence of 68 UV images of Saturn's southern aurora was obtained by the Hubble Space Telescope (HST), coordinated with measurements of the upstream interplanetary conditions made by the Cassini spacecraft. Using the poleward edge of the observed aurora as a proxy for the open-closed field line boundary, the open flux content of the southern polar region has been estimated. It is found to range from 15 to 50 GWb during the interval, such a large variation providing evidence of a significant magnetospheric interaction with the solar wind, in particular with structures associated with corotating interaction regions (CIRs). Cassini measurements of the upstream interplanetary conditions have been used to estimate the rate of open flux production at the magnetopause. By comparison with the open flux values obtained from the images, the rate of open flux closure in Saturn's magnetotail is also estimated. We find that the rate of open flux production is high (200 kV) in the high-field strength intervals following the onset of CIR-related compressions, and elevated (30-40 kV) in an intermediate-field strength rarefaction region. High flux closure rates (100-200 kV) are estimated in association with the onset of solar wind compressions and are intermittently increased (30-60 kV) during a weak-field rarefaction region. The disturbed auroral forms seen in the images are discussed in relation to the estimated reconnection rates. Recent studies have suggested that Saturn Kilometric Radiation emissions are also disturbed by the onset of CIR compressions at Saturn. [less ▲]

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See detailOpen flux estimates in Saturn's magnetosphere during the January 2004 Cassini-HST campaign, and implications for reconnection rates
Badman, S. V.; Bunce, E. J.; Clarke, J. T. et al

Conference (2005, August 07)

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