G. Sindoni

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. The 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. The extended Io “tail” persists for ~3 hours 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.

Multiple-wavelength sensing of Jupiter during the Juno mission's first perijove passage

We compare Jupiter observations made around 27 August 2016 by Junos JunoCam, Jovian Infrared Auroral Mapper (JIRAM), MicroWave Radiometer (MWR) instruments, and NASAs Infrared Telescope Facility. Visibly dark regions are highly correlated with bright areas at 5 µm, a wavelength sensitive to gaseous NH3 gas and particulate opacity at p ≤5 bars. A general correlation between 5-µm and microwave radiances arises from a similar dependence on NH3 opacity. Significant exceptions are present and probably arise from additional particulate opacity at 5 µm. JIRAM spectroscopy and the MWR derive consistent 5-bar NH3 abundances that are within the lower bounds of Galileo measurement uncertainties. Vigorous upward vertical transport near the equator is likely responsible for high NH3 abundances and with enhanced abundances of some disequilibrium species used as indirect indicators of vertical motions.

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 4–5 µm 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.

Mapping of hydrocarbons and H3+ emissions at Jupiter's north pole using Galileo/NIMS data

In this paper we report the mapping of H3+, C2H2, and CH4 as derived by an unexploited Galileo/Near-Infrared Mapping Spectrometer (NIMS) data set. As previously observed, hydrocarbons emissions appear to be located in the internal part of the auroral main oval, where CH4 3 µm vibrational band intensity ratios suggest that nonthermal excitation mechanisms, such as auroral particle precipitation and/or Joule heating, are responsible for the observed emissions. Temperature estimation are in good agreement for the CH4-emitting region on the hot spot, while the values obtained for H3+ are lower in comparison with Cassini/visual and infrared mapping spectrometer and ground-based data. C2H2 emission overlaps the CH4 one only at higher latitudes >75°N, indicating that different energetic particles are at work inside the main oval polar ward. CH4 is also found on the northern section of the main oval (135°< longitude <190°, 60°< latitude <90°N). The present investigation results have implications on the Juno/Jovian InfraRed Auroral Mapper observation planning as well as on the codes that will be used to retrieve temperatures and densities of all the emitting species involved in the Jupiter auroral processes.

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.

Stringent upper limit of CH4 on Mars based on SOFIA/EXES observations

Discovery of CH4 in the Martian atmosphere has led to much discussion since it could be a signature of biological and/or geological activities on Mars. However, the presence of CH4 and its temporal and spatial variations are still under discussion because of the large uncertainties embedded in the previous observations. We performed sensitive measurements of Martian CH4 by using the Echelon-Cross-Echelle Spectrograph (EXES) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) on 16 March 2016, which corresponds to summer (Ls = 123.2∘) in the northern hemisphere on Mars. The high altitude of SOFIA (~13.7 km) enables us to significantly reduce the effects of terrestrial atmosphere. Thanks to this, SOFIA/EXES improves our chances of detecting Martian CH4 lines because it reduces the impact of telluric CH4 on Martian CH4, and allows us to use CH4 lines in the 7.5 μm band which has less contamination. However, our results show no unambiguous detection of Martian CH4. The Martian disk was spatially resolved into 3 × 3 areas, and the upper limits on the CH4 volume mixing ratio range from 1 to 9 ppb across the Martian atmosphere, which is significantly less than detections in several other studies. These results emphasize that release of CH4 on Mars is sporadic and/or localized if the process is present.

Properties of a Martian local dust storm in Atlantis Chaos from OMEGA/MEX data

Abstract In this study we present the analysis of the dust properties of a local storm imaged in the Atlantis Chaos region on Mars by the OMEGA imaging spectrometer on March 2nd, 2005. We use the radiative transfer model MITRA to study the dust properties at solar wavelengths between 0.5 µm and 2.5 µm and infer the connection between the local storm dynamics and the topography. We retrieve maps of effective grain radius (reff), optical depth at 9.3 µm (τ9.3) and top altitude (ta) of the dust layer. Our results show that large particles (reff = 1.6 µm) are gathered in the centre of the storm (lat = 33.5° S; lon = 183.5° W), where the optical depth is maximum (τ9.3 > 7.0) and the top altitude exceeds 18 km. Outside the storm, we obtain τ9.3 We speculate that a low thermal inertia region at the western border of Atlantis Chaos is a possible source of the dust storm. Moreover, we find evidence that topography plays a role in confining the local storm in Atlantis Chaos. The vertical wind component from the GCM does not provide any hint for the triggering of dust lifting. On the other hand, the combination of the horizontal and vertical wind profiles suggests that the dust, once lifted, is pushed eastward and then downward and gets confined within the north-east ridge of Atlantis Chaos. From our results, the thickness of the dust layer collapsed on the surface ranges from about 1 µm at the storm boundaries up to more than 100 µm at its centre. We verify that a layer of dust thicker than 1 µm, deposited on the surface, can prevent the detection of mafic absorption features. However, such features are still present in OMEGA data of Atlantis Chaos registered after the storm. Hence, we deduce that, once the storm is over, the dust deposited on an area larger than the one where it has been observed.

The contribution of the ARIEL space mission to the study of planetary formation

The study of extrasolar planets and of the Solar System provides complementary pieces of the mosaic represented by the process of planetary formation. Exoplanets are essential to fully grasp the huge diversity of outcomes that planetary formation and the subsequent evolution of the planetary systems can produce. The orbital and basic physical data we currently possess for the bulk of the exoplanetary population, however, do not provide enough information to break the intrinsic degeneracy of their histories, as different evolutionary tracks can result in the same final configurations. The lessons learned from the Solar System indicate us that the solution to this problem lies in the information contained in the composition of planets. The goal of the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL), one of the three candidates as ESA M4 space mission, is to observe a large and diversified population of transiting planets around a range of host star types to collect information on their atmospheric composition. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres, which should show minimal condensation and sequestration of high-Z materials and thus reveal their bulk composition across all main cosmochemical elements. In this work we will review the most outstanding open questions concerning the way planets form and the mechanisms that contribute to create habitable environments that the compositional information gathered by ARIEL will allow to tackle.

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.