A. Olivieri

Preliminary JIRAM results from Juno polar observations: 2. Analysis of the Jupiter southern H3+ emissions and comparison with the north aurora

The Jupiter InfraRed Auroral Mapper (JIRAM) aboard Juno observed the Jovian South Pole aurora during the first orbit of the mission. H3+ (trihydrogen cation) and CH4 (methane) emissions have been identified and measured. The observations have been carried out in nadir and slant viewing both by a L-filtered imager and a 2–5xa0μm spectrometer. Results from the spectral analysis of the all observations taken over the South Pole by the instrument are reported. The coverage of the southern aurora during these measurements has been partial, but sufficient to determine different regions of temperature and abundance of the H3+ ion from its emission lines in the 3–4xa0μm wavelength range. Finally, the results from the southern aurora are also compared with those from the northern ones from the data taken during the same perijove pass and reported by Dinelli et al. (2017).

Infrared observations of Jovian aurora from Juno's first orbits: Main oval and satellite footprints

The Jovian Infrared Auroral Mapper (JIRAM) is an imager/spectrometer on board NASA/Juno mission for the study of the Jovian aurorae. n nThe first results of JIRAMs imager channel observations of the H3+ infrared emission, collected around the first Juno perijove, provide excellent spatial and temporal distribution of the Jovian aurorae, and show the morphology of the main ovals, the polar regions, and the footprints of Io, Europa and Ganymede. n nThe extended Io “tail” persists for ~3u2009hours after the passage of the satellite flux tube. Multi-arc structures of varied spatial extent appear in both main auroral ovals. Inside the main ovals, intense, localized emissions are observed. In the southern aurora, an evident circular region of strong depletion of H3+ emissions is partially surrounded by an intense emission arc. The southern aurora is brighter than the north one in these observations. Similar, probably conjugate emission patterns are distinguishable in both polar regions.

Preliminary JIRAM results from Juno polar observations: 1. Methodology and analysis applied to the Jovian northern polar region

During the first orbit around Jupiter of the NASA/Juno mission, the Jovian Auroral Infrared Mapper (JIRAM) instrument observed the auroral regions with a large number of measurements. The measured spectra show both the emission of the H3+ ion and of methane in the 3–4xa0μm spectral region. In this paper we describe the analysis method developed to retrieve temperature and column density (CD) of the H3+ ion from JIRAM spectra in the northern auroral region. The high spatial resolution of JIRAM shows an asymmetric aurora, with CD and temperature ovals not superimposed and not exactly located where models and previous observations suggested. On the main oval averaged H3+ CDs span between 1.8 × 1012xa0cm−2 and 2.8 × 1012xa0cm−2, while the retrieved temperatures show values between 800 and 950xa0K. JIRAM indicates a complex relationship among H3+ CDs and temperatures on the Jupiter northern aurora.

Preliminary results on the composition of Jupiter's troposphere in hot spot regions from the JIRAM/Juno instrument

The Jupiter InfraRed Auroral Mapper (JIRAM) instrument on board the Juno spacecraft performed observations of two bright Jupiter hot spots around the time of the first Juno pericenter passage on 27 August 2016. The spectra acquired in the 4–5u2009µm spectral range were analyzed to infer the residual opacities of the uppermost cloud deck as well as the mean mixing ratios of water, ammonia, and phosphine at the approximate level of few bars. Our results support the current view of hot spots as regions of prevailing descending vertical motions in the atmosphere but extend this view suggesting that upwelling may occur at the southern boundaries of these structures. Comparison with the global ammonia abundance measured by Juno Microwave Radiometer suggests also that hot spots may represent sites of local enrichment of this gas. JIRAM also identifies similar spatial patterns in water and phosphine contents in the two hot spots.

Preliminary JIRAM results from Juno polar observations: 3. Evidence of diffuse methane presence in the Jupiter auroral regions

Throughout the first orbit of the NASA Juno mission around Jupiter, the Jupiter InfraRed Auroral Mapper (JIRAM) targeted the northern and southern polar regions several times. The analyses of the acquired images and spectra confirmed a significant presence of methane (CH4) near both poles through its 3.3xa0μm emission overlapping the H3+ auroral feature at 3.31xa0μm. Neither acetylene (C2H2) nor ethane (C2H6) have been observed so far. The analysis method, developed for the retrieval of H3+ temperature and abundances and applied to the JIRAM-measured spectra, has enabled an estimate of the effective temperature for methane peak emission and the distribution of its spectral contribution in the polar regions. The enhanced methane inside the auroral oval regions in the two hemispheres at different longitude suggests an excitation mechanism driven by energized particle precipitation from the magnetosphere.

Characterization of the white ovals on Jupiter's southern hemisphere using the first data by the Juno/JIRAM instrument

During the first perijove passage of the Juno mission, the Jovian InfraRed Auroral Mapper (JIRAM) observed a line of closely spaced oval features in Jupiters southern hemisphere, between 30°S and 45°S. In this work, we focused on the longitudinal region covering the three ovals having higher contrast at 5xa0μm, i.e., between 120°W and 60°W in System III coordinates. We used the JIRAMs full spectral capability in the range 2.4–3xa0μm together with a Bayesian data inversion approach to retrieve maps of column densities and altitudes for an NH3 cloud and an N2H4 haze. The deep (under the saturation level) volume mixing ratio and the relative humidity for gaseous ammonia were also retrieved. Our results suggest different vortex activity for the three ovals. Updraft and downdraft together with considerations about the ammonia condensation could explain our maps providing evidences of cyclonic and anticyclonic structures.

Clusters of cyclones encircling Jupiter’s poles

The familiar axisymmetric zones and belts that characterize Jupiter’s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes. Two-dimensional turbulence in combination with the Coriolis β-effect (that is, the large meridionally varying Coriolis force on the giant planets of the Solar System) produces alternating zonal flows. The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur. Simulations with shallow-water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles. Jovian polar regions are not visible from Earth owing to Jupiter’s low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from Jupiter’s equatorial plane. Here we report that visible and infrared images obtained from above each pole by the Juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. Although migration of cyclones towards the pole might be expected as a consequence of the Coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including Saturn’s polar hexagonal features). The manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown.

Juno observations of spot structures and a split tail in Io-induced aurorae on Jupiter

Moons drive structure in Jupiters aurorae Like Earth, Jupiter has aurorae generated by energetic particles hitting its atmosphere. Those incoming particles can come from Jupiters moons Io and Ganymede. Mura et al. used infrared observations from the Juno spacecraft to image the moon-generated aurorae. The pattern induced by Io showed an alternating series of spots, reminiscent of vortices, and sometimes split into two arcs. Aurorae related to Ganymede could also show a double structure. Although the cause of these unexpected features remains unknown, they may provide a way to examine how the moons produce energetic particles or how the particles propagate to Jupiter. Science, this issue p. 774 Auroral features induced on Jupiter by the moons Io and Ganymede have complex spatial structures. Jupiter’s aurorae are produced in its upper atmosphere when incoming high-energy electrons precipitate along the planet’s magnetic field lines. A northern and a southern main auroral oval are visible, surrounded by small emission features associated with the Galilean moons. We present infrared observations, obtained with the Juno spacecraft, showing that in the case of Io, this emission exhibits a swirling pattern that is similar in appearance to a von Kármán vortex street. Well downstream of the main auroral spots, the extended tail is split in two. Both of Ganymede’s footprints also appear as a pair of emission features, which may provide a remote measure of Ganymede’s magnetosphere. These features suggest that the magnetohydrodynamic interaction between Jupiter and its moon is more complex than previously anticipated.

First Estimate of Wind Fields in the Jupiter Polar Regions From JIRAM‐Juno Images

We present wind speeds at the ~ 1 bar level at both Jovian polar regions inferred from the 5-μm infrared images acquired by the Jupiter InfraRed Auroral Mapper (JIRAM) instrument on the National Aeronautics and Space Administration Juno spacecraft during its fourth periapsis (2 February 2017). We adopted the criterion of minimum mean absolute distortion (Gonzalez & Woods, 2008) to quantify the motion of cloud features between pairs of images. The associated random error on speed estimates is 12 m/s in the northern polar region and 9.8 m/s at the south. Assuming that polar cyclones described by Adriani et al. (2018, https://doi.org/10.1038/nature25491) are in rigid motion with respect to System III, tangential speeds in the interior of the vortices increase linearly with distance from the center. The annulus of maximum speed for the main circumpolar cyclones is located at approximatively 1,000 km from their centers, with peak cyclonic speeds typically between 80 and 110 m/s and ~50 m/s in at least two cases. Beyond the annulus of maximum speed, tangential speed decreases inversely with the distance from the center within the Southern Polar Cyclone and somewhat faster within the Northern Polar Cyclone. A few small areas of anticyclonic motions are also identified within both polar regions.

Preliminary performance of Sub-Surface Radar for the EJSM/Laplace mission

The Sub-Surface Radar (SSR) instrument is a core payload for the Jupiter Ganymede Orbiter (JGO) of the EJSM, which is complementary to the Ice Penetrating Radar on board the Jupiter Europa Orbiter (JEO). These instruments work at low frequency (HF/VHF band) and are designed to penetrate the surfaces of icy moons of Jupiter. The paper will present a preliminary performance model aimed to assess the penetration capability of the instrument in different operative conditions and planets surface characteristics.