Theory of Figures to the Seventh Order and the Interiors of Jupiter and Saturn

Interior modeling of Jupiter and Saturn has advanced to a state where thousands of models are generated that cover the uncertainty space of many parameters. This approach demands a fast method of computing their gravity field and shape. Moreover, the Cassini mission at Saturn and the ongoing Juno mission delivered gravitational harmonics up to J 12. Here we report the expansion of the theory of figures, which is a fast method for gravity field and shape computation, to the seventh order (ToF7), which allows for computation of up to J 14. We apply three different codes to compare the accuracy using polytropic models. We apply ToF7 to Jupiter and Saturn interior models in conjunction with CMS-19 H/He equation of state. For Jupiter, we find that J 6 is best matched by a transition from an He-depleted to He-enriched envelope at 2–2.5 Mbar. However, the atmospheric metallicity reaches 1 × solar only if the adiabat is perturbed toward lower densities, or if the surface temperature is enhanced by ∼14 K from the Galileo value. Our Saturn models imply a largely homogeneous-in-Z envelope at 1.5–4 × solar atop a small core. Perturbing the adiabat yields metallicity profiles with extended, heavy-element-enriched deep interior (diffuse core) out to 0.4 R Sat, as for Jupiter. Classical models with compact, dilute, or no core are possible as long as the deep interior is enriched in heavy elements. Including a thermal wind fitted to the observed wind speeds, representative Jupiter and Saturn models are consistent with all observed J n values.

On the clouds and ammonia in Jupiter’s upper troposphere from Juno JIRAM reflectivity observations

ABSTRACT We analyse spectra measured by the Jovian Infrared Auroral Mapper (JIRAM, a payload element of the NASA Juno mission) in the 3150–4910 cm−1 (2.0–3.2 μm) range during the perijiove passage of 2016 August. Despite modelling uncertainties, the quality and the relative uniformity of the data set allow us to determine several parameters characterizing the Jupiter’s upper troposphere in the latitude range of 35°S–30°N. Ammonia relative humidity at 500 millibars varies between 5 per cent to supersaturation beyond 100 per cent for about 3 per cent of the processed spectra. Ammonia appears depleted over belts and relatively enhanced over zones. Local variations of ammonia, arguably associated with local dynamics, are found to occur in several locations on the planet (Oval BA, South Equatorial Belt). Cloud altitude, defined as the level where aerosol opacity reaches unit value at 3650 cm−1 (2.74 μm), is maximum over the Great Red Spot (>20 km above the 1 bar level) and the zones (15 km), while it decreases over the belts and towards higher latitudes. The aerosol opacity scale height suggests more compact clouds over zones and more diffuse clouds over belts. The integrated opacity of clouds above the 1.3-bar pressure level is found to be minimum in regions where thermal emission of the deeper atmosphere is maximum. The opacity of tropospheric haze above the 200-mbar level also increases over zones. Our results are consistent with a Hadley-type circulation scheme previously proposed in literature for belts and zones, with clear hemisphere asymmetries in cloud and haze.

Jupiter's envelope is not homogeneous

<p>The amount and distribution of heavy elements in Jupiter’s interior is crucial to understand how the planet was formed and evolved. The results provided by the Juno mission in the last years have fundamentally changed our view of the interior of Jupiter. The remarkably accurate gravity data, including odd gravity harmonics, have allowed us to put constrains on the zonal flows, the extent of differential rotation and lead us to find that Jupiter has most likely a dilute core. In this study we do interior structure calculations using a Bayesian statistical approach and fitting all observational constrains, to show that a non-homogenous envelope is also a constraint set up by the Juno measurements, which is helping us to get closer to unveiling Jupiter’s deep secrets. </p>

Comparing energetic particle loss processes in the magnetospheres of Jupiter and Saturn using Energetic Neutral Atom (ENA) remote sensing

<p>The dedicated Energetic Neutral Atom (ENA) imager on the Cassini spacecraft provided indispensable measurements of magnetospheric processes at Saturn. At Jupiter, Cassini provided only a few serendipitous ENA images as the spacecraft flew by Jupiter at large radial distances.  The Juno spacecraft, now in a polar orbit around Jupiter, carries no ENA camera, but the energetic particle JEDI instrument is sensitive to ENA’s with energies > 50 keV, provided there are few charged particles in the environment to mask their presence.  Even with limited ENA capabilities, the Juno mission has revealed important differences between Saturn and Jupiter with regard to how charged ions are lost from these magnetospheric systems. Specifically, a major contribution to ENA emissions at Jupiter come from Jupiter’s polar atmosphere. These ENAs likely arise from energetic ions that nearly precipitate in the auroral zone, only to mirror magnetically within the atmosphere where they charge exchange with atoms in Jupiter’s upper atmosphere. Cassini did not observe this precipitating component at Saturn despite the abundance of quality ENA measurements obtained there. We conclude that ion precipitation into Jupiter’s atmosphere is competitive with other loss processes.  In contrast, in the Saturn system, it is likely that losses associated with the dense neutral gas populations near the equator dominate the loss of energetic particles.</p>

The evolution of Jupiter polar cyclones

<p>JIRAM (the Jovian InfraRed Auroral Mapper) is an infrared camera and<br>spectrometer on board Juno. JIRAM operates in the 2-5 μm spectral<br>range and is built to observe both Jupiter's infrared aurora and its<br>atmosphere. Since 2016, JIRAM has performed several observations of<br>the polar regions of the planet, thanks to the unique orbital design<br>of the Juno mission.  In the north polar region, Juno discovered, in<br>2017, the presence of an eight-cyclone structure around a single polar<br>cyclone; to the south, a polar cyclone is surrounded by five<br>circumpolar cyclones. The stability of these structures has been<br>monitored for almost 4 years. Recent observations, made at the end of<br>2019, showed that the configuration of the South Pole has temporarily<br>changed: the structure moved in a hexagon for a few months, before<br>returning to its original pentagonal shape. To the north, there are<br>significant hints that the octagonal shape may have been lost for a<br>similar period of time.<br>We find that all cyclones show a very slow, westward drift as a rigid<br>ensemble, and, in addition, they oscillate around their rest position<br>with similar timescales. These oscillations seem to propagate from<br>cyclone to cyclone. The implications of these transient deviations<br>from the symmetrical forms, which appear to be an apparent condition<br>of equilibrium, are discussed.</p>

Recent JunoCam Revelations About Discrete Features in Jupiter’s Atmosphere

<p>JunoCam, the visible imager on the Juno mission’s payload that was designed primarily for public-outreach purposes, continues to produce images of Jupiter that provide unexpected scientific benefits.  Juno’s polar orbits enable observing regions of the planet that have not previously been detected at such high resolution by any previous spacecraft. JunoCam has a single CCD detector with an integral color-strip filter that enables the instrument to image in four color bands—blue, green, red and an 889-nm methane band.  JunoCam maps a field of view of 58° across the width of the detector, perpendicular to the spacecraft scan direction. We will describe characteristics and likely origins of bright white compact (~50 km) clouds, informally dubbed “pop-up” clouds by the JunoCam team.  We used the length of shadows of these and other features to determine the relative heights of clouds and assigned a provisional chemical classification based on relative altitudes from equilibrium-chemistry predictions. We tracked the continued interactions of small anticyclonic ovals with Jupiter’s Great Red Spot (GRS) that drew off high-altitude reddish haze into strips (commonly called “flakes”) on its western edge.  A lightning flash was detected in one of the compact circumpolar cyclones in late December. Observations of the south-polar circumpolar cyclones showed that the original unequally sided pentagon becoming a hexagon – with a cyclone filling in an open area, then a pentagon again over the course of 110 days.  In a collaboration with amateur astronomer Clyde Foster (S. Africa), we observed the morphology of an unexpected upwelling in late May of 2020, now known as “Clyde’s Spot”, and tracked its evolution in concert with several ground-based observations.  We also measured ~40-50 m/s winds around the sinuous jet bounding the South Polar Hood, an upper-level haze generated by auroral-related chemistry.  Lightly processed and raw JunoCam data continue to be posted on the JunoCam webpage at https://missionjuno.swri.edu/junocam/processing.   Citizen scientists download these images and upload their processed contributions.</p>

Asteroid masses obtained with INPOP planetary ephemerides

<p>We present here masses of 103 asteroids deduced from their perturbations on the<br />orbits of the inner planets, in particular Mars and the Earth. These determinations and the<br />INPOP19a planetary ephemerides are improved by the recent Mars orbiter navigation data<br />and the updated orbit of Jupiter based on the Juno mission data. More realistic mass estimates<br />are computed by a new method based on random Monte-Carlo sampling that uses up-to-date<br />knowledge of asteroid bulk densities. We provide masses with uncertainties better than 33%<br />for 103 asteroids. Deduced bulk densities are consistent with those observed within the main<br />spectroscopic complexes.</p>

Juno Diagnosis of Magnetospheric Dynamics at Jupiter with Energetic Neutral Atoms

<p>Energetic Neutral Atom (ENA) cameras on orbiting spacecraft at Earth and Saturn have helped greatly to diagnose these complex magnetospheres. Within this decade, the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) mission will arrive at Jupiter and make ENA imaging a major thrust in helping to understand its complex magnetosphere. The present polar-orbiting Juno mission carries no ENA camera, but the energetic particle JEDI instrument is serendipitously sensitive to ENA’s with energies > 50 keV, provided there are no charged particles in the environment to mask their presence. Juno offers great service to the interpretation of both past and future ENA imaging with its orbit allowing unique viewing perspectives. Here we report on several components of ENA emissions that can probe the dynamical state of the regions involved, including the space environment of the orbit of Io, that of Europa, and Jupiter itself. A special focus here will be new observations of ENA emissions from Jupiter’s polar regions, the proper interpretation of which may end up being unique to the Juno mission, even after the JUICE mission.</p>