The interior structure of Saturn, the depth of its winds, and the mass and age of its rings constrain its formation and evolution. In the final phase of the Cassini mission, the spacecraft dived ...between the planet and its innermost ring, at altitudes of 2600 to 3900 kilometers above the cloud tops. During six of these crossings, a radio link with Earth was monitored to determine the gravitational field of the planet and the mass of its rings. We find that Saturn's gravity deviates from theoretical expectations and requires differential rotation of the atmosphere extending to a depth of at least 9000 kilometers. The total mass of the rings is (1.54 ± 0.49) × 10
kilograms (0.41 ± 0.13 times that of the moon Mimas), indicating that the rings may have formed 10
to 10
years ago.
The combination of the Doppler data from the first two Juno science orbits provides an improved estimate of the gravity field of Jupiter, crucial for interior modeling of giant planets. The ...low‐degree spherical harmonic coefficients, especially J4 and J6, are determined with accuracies better than previously published by a factor of 5 or more. In addition, the independent estimates of the Jovian gravity field, obtained by the orbits separately, agree within uncertainties, pointing to a good stability of the solution. The degree 2 sectoral and tesseral coefficients, C2,1, S2,1, C2,2, and S2,2, were determined to be statistically zero as expected for a fluid planet in equilibrium.
Key Points
The Jupiter gravity field has been evaluated for the first two Juno orbits
The zonal harmonics J4 and J6 improve over previous results by factors of 5 and 22, respectively, providing strong constraints on Jupiter interior models
Context
. The upcoming JUICE and Europa Clipper missions targeting Jupiter’s Galilean satellites will provide radio science tracking measurements of both spacecraft. Such data are expected to ...significantly help estimating the moons’ ephemerides and related dynamical parameters (e.g. tidal dissipation parameters). However, the two missions will yield an imbalanced dataset, with no flybys planned at Io, condensed over less than six years. Current ephemerides’ solutions for the Galilean moons, on the other hand, rely on ground-based astrometry collected over more than a century which, while being less accurate, bring very valuable constraints on the long-term dynamics of the system.
Aims
. An improved solution for the Galilean satellites’ complex dynamics could however be achieved by exploiting the existing synergies between these different observation sets.
Methods
. To quantify this, we merged simulated radio science data from both JUICE and Europa Clipper spacecraft with existing ground-based astrometric and radar observations, and performed the inversion in different configurations: either adding all available ground observations or individually assessing the contribution of different data subsets. Our discussion specifically focusses on the resulting formal uncertainties in the moons’ states, as well as Io’s and Jupiter’s tidal dissipation parameters.
Results
. Adding astrometry stabilises the moons’ state solution, especially beyond the missions’ timelines. It furthermore reduces the uncertainties in 1/
Q
(inverse of the tidal quality factor) by a factor two to four for Jupiter, and about 30–35% for Io. Among all data types, classical astrometry data prior to 1960 proved particularly beneficial. Overall, we also show that ground observations of Io add the most to the solution, confirming that ground observations can fill the lack of radio science data for this specific moon.
Conclusions
. We obtained a noticeable solution improvement when making use of the complementarity between all different observation sets. The promising results obtained with simulations thus motivate future efforts to achieve a global solution from actual JUICE and Clipper radio science measurements.
The gravity harmonics of a fluid, rotating planet can be decomposed into static components arising from solid-body rotation and dynamic components arising from flows. In the absence of internal ...dynamics, the gravity field is axially and hemispherically symmetric and is dominated by even zonal gravity harmonics J
that are approximately proportional to q
, where q is the ratio between centrifugal acceleration and gravity at the planet's equator. Any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. The odd harmonics, J
, J
, J
, J
and higher, are a measure of the depth of the winds in the different zones of the atmosphere. Here we report measurements of Jupiter's gravity harmonics (both even and odd) through precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter. We find a north-south asymmetry, which is a signature of atmospheric and interior flows. Analysis of the harmonics, described in two accompanying papers, provides the vertical profile of the winds and precise constraints for the depth of Jupiter's dynamical atmosphere.
On 29 September 2022 the Juno spacecraft flew within 354 km of Europa's surface while several instruments probed the moon's surroundings. During the close flyby, radio occultations were performed by ...collecting single‐frequency Doppler measurements. These investigations are essential to the study of Europa's ionosphere and represent the first repeat sampling of any set of conditions since the Galileo era. Ingress measurements resulted in a marginal detection with a peak ionospheric density of 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude. A more significant detection emerged on egress, with a peak density of 6,000 ± 3,000 cm−3 (3σ) at 320 km altitude. Comparison with Galileo measurements reveals a consistent picture of Europa's ionosphere, and confirms its dependence on illumination conditions and position within Jupiter's magnetosphere. However, the overall lower densities measured by Juno suggest a dependence on time of observation, with implications for the structure of the neutral atmosphere.
Plain Language Summary
On 29 September 2022, NASA's Juno spacecraft flew very close to Jupiter's moon Europa. During the encounter, a radio occultation experiment was performed, where radio signals are exchanged between the spacecraft and ground stations as the former sets behind or rises from the moon as seen from the Earth. The scope of this experiment was studying the ionosphere of Europa, a layer of electrons and ions surrounding the moon. The Juno measurements confirmed the presence of the layer, with a structure similar to the one observed by the Galileo mission in the late 1990s.
Key Points
Europa's ionosphere was detected from Juno's X‐band Doppler data via NASA's Deep Space Network during a close encounter in 2022
Peak densities were 4,000 ± 3,700 cm−3 (3σ) at 22 km altitude during ingress and 6,000 ± 3,000 cm−3 (3σ) at 320 km during egress
The Juno ionospheric profiles are consistent with Galileo measurements, and show a dependence on solar zenith and magnetospheric ram angles
The jovian moon Io disperses about 1 ton/s of material in the planetary magnetosphere, mainly by sublimation of SO2 from the surface and by its intense volcanic activity. The ejected material ...supplies the plasma cloud surrounding Jupiter known as Io Plasma Torus (IPT). The radio communication between Juno and the Earth DSN station crosses the IPT near the closest approach. Being a dispersive medium, the IPT introduces a path delay in the signal, which can be analyzed to retrieve the density distribution of electrons. We used radio tracking data from the first 25 orbits to investigate the morphology of the IPT and its variability. We adopted a static and axisymmetric model for the electron density and we updated it including temporal and longitudinal variability. We found that our best fit model must include both variabilities, even though on average the morphology of the IPT agrees with previous analyses. Our results suggest that the density of the outer region of the IPT fluctuates over 50% the average value over a typical time scale of about 420 days.
Key Points
Density distribution of electrons in the Io plasma torus is derived from the first 15 radio occultations by Juno
Temporal and longitudinal variabilities in the electron density of the torus are presented
Density in the Io torus fluctuates over about 50% the average value and the typical time scale of periodic variation is about 430 days
“LICIACube – the Light Italian Cubesat for Imaging of Asteroids” is managed by the Italian Space Agency (ASI) and will be part of the NASA DART mission, with the aim of i) documenting the DART ...impact’s effects on the secondary member of the (65803) Didymos binary asteroid system, ii) characterizing the shape of the target, and iii) performing dedicated scientific investigations on it. DART probe will be launched at the end of 2021 and LICIACube will be hosted as piggyback during the interplanetary cruise, then released 10 days before the impact, and autonomously guided along its fly-by trajectory. The LICIACube payload is composed by LEIA, a narrow FoV camera, and LUKE, a wide FoV imager with an RGB Bayer pattern filter, that will collect and transmit to Earth several unique images of the effects of the DART impact on the asteroid, such as the formation and the development of the plume potentially determined by the impact.
LICIACube will be the first deep space mission developed and autonomously managed by an Italian team: the design, integration and test of the CubeSat have been assigned by ASI to the aerospace company Argotec, while the LICIACube Ground Segment has a complex architecture based on the Argotec Mission Control Center, antennas of the NASA Deep Space Network and data archiving and processing, managed at the ASI Space Science Data Center. The LICIACube team includes a wide Italian scientific community, involved in the definition of all the aspects of the mission: trajectory design; mission definition (and real-time orbit determination during operations); impact, plume and imaging simulation and modelling, in preparation of a suitable framework for the analysis and interpretation of in-situ data. The major technological mission challenge, i.e. the autonomous targeting and imaging of such a small body during a fast fly-by, to be accomplished with the limited resources of a CubeSat, is affordable thanks to a strong synergy of all the mentioned teams in support of the engineering tasks.
-LICIACube is the first purely Italian spacecraft operating in deep space.-LICIACube is managed by the Italian Space Agency and will be part of the NASA DART mission.-It will analyze the output of the first kinetic impact test at a realistic scale.-The payload is composed by LEIA, a narrow FoV camera, and LUKE, a wide FoV imager with an RGB Bayer pattern filter.-Aims: documenting the DART impact on Dimorphos; characterizing the target shape; performing scientific investigations.
Gelatin is a natural protein with many desirable properties for application as a biomaterial, including scaffolding for tissue engineering. In this work gelatin A with a molecular weight in the range ...50−100 kg mol-1 was modified with methacrylic anhydride and processed into a concentrated oil-in-water emulsion. Polymerization of the continuous phase gave rise to a polyHIPE, a porous material possessing a highly interconnected, trabecular morphology. In the paper, we focused on the goal of obtaining matrixes characterized by suitable sizes of both voids and interconnects, to allow an in depth colonization from transplanted cells. In this respect, we investigated the role of the volume percentage of the dispersed phase and the effect of additives. It was established that high pore volumes (≥90%) are to be preferred, because they allow the production of solid foams characterized by average void and interconnect diameters of approximately 20 and 10 μm, respectively. These values are still inadequate for the intended application of these scaffolds but represent a good starting point for further improvements. These were achieved through the use of additives, namely sodium chloride and dimethyl sulfoxide, which partially destabilized the precursor emulsion and allowed a solid foam to be obtained with void and interconnect diameters in the range of 30−150 μm and 10−50 μm, respectively.
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