Cassini UVIS time-resolved Jupiter auroral data compared to QP radio bursts

Poster (2003)

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Jupiter in a 4-sec integration "high time-resolution mode" on Jan 8, 13-14, and 20-21 in 2001. In this mode Extreme-Ultraviolet and Far ... [more ▼]

The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed Jupiter in a 4-sec integration "high time-resolution mode" on Jan 8, 13-14, and 20-21 in 2001. In this mode Extreme-Ultraviolet and Far-Ultraviolet spectra were obtained with reduced spectral and spatial resolution in order to study rapid variations in H2 band and H Lyman alpha emission. Previous work has shown that the region inside Jupiter's main auroral ovals contains highly variable spots of emission (auroral flares) that persist for typically 1 or 2 minutes. This duration is similar to that in Jupiter's quasi-periodic (QP) radio bursts. We compare UVIS data to simultaneous Galileo Plasma Wave Subsystem (PWS) and Cassini Radio PWS (RPWS) observations. Jan 8 was an active period for UV variability, that we associate with polar auroral flares. There is a correlation between the radio and UV bursts in this period, suggesting that they are related phenomena. We will also explore coordinated Hubble Space Telescope Imaging Spectrograph time-tagged UV images from Jan 13-14 and Jan 20-21, 2001 to study the spatial properties of the auroral flares. [less ▲]

Excitation of the FUV Io tail on Jupiter: Characterization of the electron precipitation

in Journal of Geophysical Research. Space Physics (2002), 107(A11),

[1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to ... [more ▼]

[1] Spectral observation of both polar regions of Jupiter in the far ultraviolet (FUV) obtained with the Space Telescope Imaging Spectrograph (STIS), on board the Hubble Space Telescope from July 1997 to January 2001 have been combined with FUV images to map the FUV color ratio along the STIS slit. Spatially resolved spectra of the aurora carried at similar to12 Angstrom resolution have been used to determine the amount of methane absorption as measured by the FUV color ratio of the Io magnetic footprint and its trailing tail. It is found that the absorption is systematically less than in the main polar aurora, indicating a higher altitude source region. The color ratio of the north tail is shown to slowly decrease downstream from the footprint. The combination of these spectral data with a two-stream model of the interaction of energetic electrons with the Jovian thermosphere indicates that the mean energy of the electrons creating the north FUV emission ranges from similar to55 keV at the Io footprint to similar to40 keV, 20 degrees downstream in the tail. In parallel, the incident electron energy flux drops by a factor similar to6 over the same angular distance. These observations are consistent with the steady state slippage picture where the subcorotating flux tube is accelerated very slowly up to corotation owing to the nonideal coupling. It is argued that small deviations from corotation can supply sufficient energy to fuel the observed auroral emissions. It is suggested that the parallel electric field accelerating electrons out of the flux tube only moderately depends on the time elapsed since the contact with Io, although the mapping between a point in the tail and Io is very uncertain in the presence of magnetic field line slippage. [less ▲]

The HST Campaign on Jupiter's Aurora during the Cassini Flyby

Conference (2002, July 29)

Map of the precipitated electron mean energy in the Jovian aurora

Conference (2002, June 17)

The HST Campaign on Jupiter's Aurora during the Cassini Flyby

Conference (2002, June 17)

Ultraviolet emissions from the magnetic footprints of Io, Ganymede and Europa on Jupiter

in Nature (2002), 415(6875), 997-1000

Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates(1-3). The specific physical mechanisms ... [more ▼]

Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates(1-3). The specific physical mechanisms responsible for generating those emissions are not well understood, but in general the spot seems to arise because of an electromagnetic interaction between Jupiter's magnetic field and the plasma surrounding Io, driving currents of around 1 million amperes down through Jupiter's ionosphere(4-6). The other galilean satellites may also leave footprints, and the presence or absence of such footprints should illuminate the underlying physical mechanism by revealing the strengths of the currents linking the satellites to Jupiter. Here we report persistent, faint, far-ultraviolet emission from the jovian footprints of Ganymede and Europa. We also show that Io's magnetic footprint extends well beyond the immediate vicinity of Io's flux-tube interaction with Jupiter, and much farther than predicted theoretically(4-6); the emission persists for several hours downstream. We infer from these data that Ganymede and Europa have persistent interactions with Jupiter's magnetic field despite their thin atmospheres. [less ▲]

Chandra X-ray Observations of the Jovian System

Conference (2002)

High-spatial resolution Chandra x-ray obsrvations have demonstrated that most of Jupiter's northern auroral x-rays come from a hot spot located significantly poleward of the latitudes connected to the ... [more ▼]

High-spatial resolution Chandra x-ray obsrvations have demonstrated that most of Jupiter's northern auroral x-rays come from a hot spot located significantly poleward of the latitudes connected to the inner magnetosphere. This hot spot appears fixed in magnetic latitude and longitude and coincides with a region exhibiting anomalous ultraviolet and infrared emissions. The hot spot also exhibited approximately 45 minute quasi-periodic oscillations, a period similar to those reported for high-latitude radio and energetic electron bursts observed by near-Jupiter spacecraft. These results invalidate the idea that jovian auroral x-ray emissions are mainly excited by steady precipitation of energetic heavy ions from the inner magnetosphere. Instead, the x-rays appear to result from currently unexplained processes in the outer magnetosphere that produce highly localized and highly variable emissions over an extremely wide range of wavelengths. The Chandra observations also revealed for the first time x-ray emission (about 0.1 GW) from the Io Plasma Torus, as well as very faint x-ray emission (about 1-2 MW) from the Galilean moons Io, Europa, and possibly Ganymede. The emission from the moons is almost certainly due to Kalpha emission of surface atoms (and possibly impact atoms) excited by the impact of highly energetic protons, oxygen, and sulfur atoms and ions from the Torus. The Torus emission is less well understood at present, although bremsstrahlung from the non-thermal tail of the electron distribution may provide a significant fraction. In any case, further observations, already accepted and in the process of being planned, with Chandra, some with the moderate energy resolution of the CCD camera, together with simultaneous Hubble Space Telescope observations and hopefully ground-based IRTF observations should soon provide greater insight into these various processes. [less ▲]

Observations of the Jovian System with the Chandra X-ray Observatory

Conference (2002)

Sensitive, very high spatial-resolution x-ray observations with the Chandra X-ray Observatory have revealed that Jupiter's northern x-ray aurora originates at a spot fixed in a coordinate system rotating ... [more ▼]

Sensitive, very high spatial-resolution x-ray observations with the Chandra X-ray Observatory have revealed that Jupiter's northern x-ray aurora originates at a spot fixed in a coordinate system rotating with the planet at latitude (60-70 deg north) and longitude (160-180 deg System III). The northern auroral x-ray emission varies with a period about 45 minute and has an average power of about 1 GW. Jupiter's disk also emits x-rays with a power of about 2 GW, perhaps resulting from reprocessing of solar x-rays in its atmosphere. These observations reveal for the first time x-ray emission from the Io Plasma Torus, with a power of about 0.1 GW. Finally, we report the discovery of very faint (about 1-2 MW) soft x-ray emission from the Galilean satellites Io, Europa, and probably Ganymede. [less ▲]

Discovery of soft X-ray emission from Io, Europa, and the Io Plasma Torus

in Astrophysical Journal (2002), 572(2), 1077-1082

We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV ... [more ▼]

We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV) H, O, and S ions from the region of the IPT seems to be the likely source of the X-ray emission from the Galilean satellites. According to our estimates, fluorescent X-ray emission excited by solar X-rays, even during flares from the active Sun, charge-exchange processes, previously invoked to explain Jupiter's X-ray aurora and cometary X-ray emission, and ion stripping by dust grains fail to account for the observed emission. On the other hand, bremsstrahlung emission of soft X-rays from nonthermal electrons in the few hundred to few thousand eV range may account for a substantial fraction of the observed X-ray flux from the IPT. [less ▲]

Transient aurora on Jupiter from injections of magnetospheric electrons

in Nature (2002), 415(6875), 1003-1005

Energetic electrons and ions that are trapped in Earth's magnetosphere can suddenly be accelerated towards the planet(1-5). Some dynamic features of Earth's aurora (the northern and southern lights) are ... [more ▼]

Energetic electrons and ions that are trapped in Earth's magnetosphere can suddenly be accelerated towards the planet(1-5). Some dynamic features of Earth's aurora (the northern and southern lights) are created by the fraction of these injected particles that travels along magnetic field lines and hits the upper atmosphere(4). Jupiter's aurora appears similar to Earth's in some respects; both appear as large ovals circling the poles and both show transient events(6-11). But the magnetospheres of Jupiter and Earth are so different-particularly in the way they are powered-that it is not known whether the magnetospheric drivers(12) of Earth's aurora also cause them on Jupiter. Here we show a direct relationship between Earth-like injections of electrons in Jupiter's magnetosphere and a transient auroral feature in Jupiter's polar region. This relationship is remarkably similar to what happens at Earth, and therefore suggests that despite the large differences between planetary magnetospheres, some processes that generate aurorae are the same throughout the Solar System. [less ▲]