Hubble observations of Jupiter’s north–south conjugate ultraviolet aurora

Abstract

a b s t r a c tComparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a statistical basis or were not obtained with high sensitivity and resolution. Such observations are important to discriminate between different mechanisms responsible for the electron acceleration of the different components of the aurora such as the satellite footprints, the «main oval» or the polar emissions. The field of view of the ACS and STIS cameras on board HST is not wide enough to provide images of the full jovian disk. We thus compare the morphology of the north and south aurora observed 55 min apart and we point out similarities and differences. On one occasion HST pointed successively the two polar regions and auroral images were seen separated by only 3 min. This makes it possible to compare the emission structure and the emitted FUV power of corresponding regions. We find that most morphological features identified in one hemisphere have a conjugate counterpart in the other hemisphere. However, the power associated with conjugate regions of the main oval, diffuse or discrete equatoward emission observed quasi-simultaneously may be different in the two hemispheres. It is not directly nor inversely proportional to the strength of the B-field as one might expect for diffuse precipitation or field-aligned acceleration with equal ionospheric electron density in both hemispheres. Finally, the lack of symmetry of some polar emissions suggests that some of them could be located on open magnetic field lines.

Jupiter’s magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits

“…The overall aurora brightness level is somewhat dim, but not atypically so [37], and the UV color ratio values are similar to previous observations [26,27]. While there is much similarity between UV and IR auroras, there are differences related to the emission mechanisms at work in both cases.…”

Statistical analysis of 26 yr of observations of decametric radio emissions from Jupiter

“…If non-Io emission comes from an extended source, the visibility of the source that results from the convolution of its extent in latitude and longitude with its beaming pattern ) would correspond to a large effective beam, which is detected as longer duration events. The fact that it is not the case suggests that non-Io emission is related to small-scale, possibly bursty auroral structures that are seen, for example, as bright spots in the UV (Prangé et al 1998;Gérard et al 2013), rather than as the radio counterparts of the main auroral oval as a whole. One reason for the lack of main oval radio emission may be related to the energy of precipitating electrons there (100s keV, Gérard et al 2014;Gustin et al 2016), which appears to be larger than optimal for the CMI.…”

Transient small‐scale structure in the main auroral emission at Jupiter

“…The small‐scale feature often appears within the duskward edge of the discontinuity. Therefore, the presence of this feature might influence the apparent length of the discontinuity, which was discussed based on north–south quasi‐simultaneous auroral observations [ Gérard et al ., ].…”