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Abstract Of the 97 known satellites in the Jovian system, the individual masses and densities of each moon have only been determined for six of them: the four Galileans, Amalthea, and Himalia. In this Letter, we derive a prediction for the mean density (and mass) of Thebe, Jupiter’s sixth-largest regular moon, obtaining a lower limit ofρ_T≳ 1.0 g cm^–3(m_T≳ 5 × 10²⁰g). In particular, this value emerges as a key constraint within the context of the resonant transport model for the origins of Jupiter’s interior satellites. Expanding on this theory, here we carry out simulations of the simultaneous gravitational shepherding of Amalthea and Thebe via the resonant influence of inward-migrating Io during Jupiter’s disk-bearing epoch. We find that owing to overstability of resonant dynamics facilitated by the circumjovian disk’s aerodynamic drag, Thebe’s smaller radius (compared to that of Amalthea) requires a higher density to ensure its terminal orbital distance exceeds that of Amalthea, as it does today. With multiple current and upcoming space missions devoted to in situ exploration of the Jovian system, a proper measurement of Thebe’s mass provides an avenue toward empirical falsification or confirmation of our theoretical model for the dynamical evolution of Jupiter’s inner moons. 

Abstract The sub-Jovian exoplanet WASP-107b ranks among the best-characterized low-density worlds, featuring a Jupiter-like radius and a mass that lies firmly in the sub-Saturn range. Recently obtained JWST spectra reveal significant methane depletion in the atmosphere, indicating that WASP-107b’s envelope has both a high metallicity and an elevated internal heat flux. Together with a detected nonzero orbital eccentricity, these data have been interpreted as evidence of tidal heating. However, explaining the observed luminosity with tidal dissipation requires an unusually low tidal quality factor ofQ∼ 100. Moreover, we find that secular excitation by the radial-velocity-detected outer companion WASP-107c generally cannot sustain WASP-107b’s eccentricity in steady state against tidal circularization. As an alternative explanation, we propose that ohmic dissipation—generated by interactions between zonal flows and the planetary magnetic field in a partially ionized atmosphere—maintains the observed thermal state. Under nominal assumptions for the field strength, atmospheric circulation, and ionization chemistry, we show that ohmic heating readily accounts for WASP-107b’s inflated radius and anomalously large internal entropy. 

Abstract Forming giant planets are accompanied by circumplanetary disks, as indicated by considerations of angular momentum conservation, observations of candidate protoplanets, and the satellite systems of planets in our Solar System. This paper derives surface density distributions for circumplanetary disks during the final stage of evolution when most of the mass is accreted. This approach generalizes previous treatments to include the angular momentum bias for the infalling material, more accurate solutions for the incoming trajectories, corrections to the outer boundary condition of the circumplanetary disk, and the adjustment of newly added material as it becomes incorporated into the Keplerian flow of the pre-existing disk. These generalizations lead to smaller centrifugal radii, higher column density for the surrounding envelopes, and higher disk accretion efficiency. In addition, we explore the consequences of different angular distributions for the incoming material at the outer boundary, with the concentration of the incoming flow varying from polar to isotropic to equatorial. These geometric variations modestly affect the disk surface density, but also lead to substantial modification to the location in the disk where the mass accretion rate changes sign. This paper finds analytic solutions for the orbits, source functions, surface density distributions, and the corresponding disk temperature profiles over the expanded parameter space outlined above. 

The formation and early evolution of Jupiter played a pivotal role in sculpting the large-scale architecture of the Solar System, intertwining the narrative of Jovian early years with the broader story of the Solar System's origins. The details and chronology of Jupiter's formation, however, remain elusive, primarily due to the inherent uncertainties of accretionary models, highlighting the need for independent constraints. Here we show that, by analysing the dynamics of Jupiter's satellites concurrently with its angular-momentum budget, we can infer Jupiter's radius and interior state at the time of the protosolar nebula's dissipation. In particular, our calculations reveal that Jupiter was 2 to 2.5 times as large as it is today, 3.8 Myr after the formation of the first solids in the Solar System. Our model further indicates that young Jupiter possessed a magnetic field of B♃† ≈ 21 mT (a factor of ~ 50 higher than its present-day value) and was accreting material through a circum-Jovian disk at a rate of M ̇ =1.2-2.4 M♃ Myr−1. Our findings are fully consistent with the core-accretion theory of giant-planet formation and provide an evolutionary snapshot that pins down properties of the Jovian system at the end of the protosolar nebula's lifetime.