OPS9
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Juno’s Microwave Radiometer (MWR) is providing an unprecedented opportunity to explore the dynamical properties and composition of Jupiter’s atmosphere well below its cloud tops. Jupiter’s atmosphere is arguably the most visibly heterogeneous and time variable in the solar system. Since its arrival on 2016 August 27, the MWR has observed variability in microwave emission at wavelengths between 1.3 and 50 cm, sensing from 0.7 bar to over 100 bars of atmospheric pressure at over 69 close approaches to the atmosphere, known as “perijoves”. There has been a concerted effort to collect contextual information from other Juno instruments, as well as ground- and space-based observations to help interpret the MWR results. The space-based observations have included those from Juno’s own visible camera (JunoCam) and its Jupiter Infrared Auroral Mapper (JIRAM), as well as the Hubble Space Telescope (HST). The ground-based observations have included images and spectra from both professional and citizen-science astronomers.
We report here observations that are constrained to spatial resolutions of 2° in latitude or better, and have been subject to recent improvements in the calibration drift for all MWR’s channels with an improved relative calibration uncertainty of 0.5% or better over the entire mission. These are shown in Figure 1 for the MWR observations covering planetocentric latitudes from 40°S to 80°N. This has allowed us to evaluate zonal-mean temperatures and variability with improved confidence that these are real and not an artifact of receiver drift. The region that shows the greatest variability from a zonal mean is the North Equatorial Belt, (NEB: 12°N-16°N) with a 2% standard deviation from the mean at all levels sensed by the MWR except for the 50-cm channel that senses variability in temperature and ammonia and water composition at pressures in excess of 100 bars of pressure. Among the strongest variability associated with discrete features in the atmosphere is a major upwelling and subsequent clearing of cloud cover in the North Temperate Belt (NTB: 20°N-26°N) in August-September of 2020. In general, the microwave brightness temperature variability often but not always correlates with visible or near- to mid-infrared variability. In some regions, such as the Equatorial Zone (EZ: 3°S-6°N), substantial variability is detected not only in regions above the level of the water-condensate cloud (~10 bars) but also at great depth (>100 bars). Current work is focusing on identifying where variabilities in the zonal-mean microwave brightness are the result of zonally discrete features in the atmosphere, particularly the NEB. Future work will address observations fulfilling the same spatial resolution requirements but covering higher northern latitudes.
Figure 1. Composite MWR maps of observed zonal-mean antenna temperatures in all channels that cover planetocentric latitudes 40°S to 80°N with 2° meridional resolution, interpolated to a common emission angle of 47°. Maps have been expanded by 0.1 year for visibility. White circles denote the actual date of the measurements, with the responsible perijove indicated at the bottom. Rightmost panels display the zonal-mean temperatures over all perijoves, together with the associated standard deviation. Unfilled spots in the maps correspond to spacecraft attitudes that precluded MWR observations being made at the required spatial resolution. Note that Channels1 and 2 have angular resolutions (“footprints”) twice the size of Channels 3-6; keeping a 2° latitude resolution for those channels thus restricts their coverage relative to Channels 3-6.
How to cite: Orton, G., Zhang, Z., Levin, S., Fletcher, L., Oyafuso, F., Li, C., Brueshaber, S., Wong, M. H., Momary, T., Bolton, S., Baines, K., Dahl, E., and Sinclair, J.: Juno Microwave Radiometer Measurements of the Depths of Spatial and Temporal Variability in Jupiter , EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-243, https://doi.org/10.5194/epsc-dps2025-243, 2025.
Introduction: The Juno mission has provided the community with accurate measurements of Jupiter’s gravitational field, providing tighter constraints for interior models. Structure models that fit Juno data find that the planet is inhomogeneous in composition and consists of a fuzzy core. Several scenarios for the formation of Jupiter’s fuzzy core were proposed, including the concurrent accretion of heavy elements and H-He gas, core erosion by large-scale or double-diffusive convection and a giant impact that mixed the primordial heavy-element core, distributing the heavy elements beyond the central region. While the possibility of forming Jupiter’s fuzzy core via a giant impact has been studied in prior work [1,2], further investigations of this scenario are required, as each study was limited in several aspects. In this study, we re-asses the giant impact scenario while considering the constraints imposed by using N-body formation simulations, smoothed particle hydrodynamics (SPH) impact simulations with state-of-the-art equations of state and high resolution, and post-impact thermal evolution simulations.
Methods: To assess the expected impact conditions between proto-Jupiter and large embryos, we use an N-body code developed by [3] based on the IAS15 integrator. We simulate the evolution of 10 embryos of the local isolation mass, separated by 5 or 8 mutual Hill radii with different initial inclinations. The simulation uses the gaseous disk model and the growth model of proto-Jupiter from [4] as well as tidal damping of embryos.
We simulate the impacts using an SPH code based on pkdgrav3 [5], derived from the Lagrangian including corrections for variable smoothing length with a kernel that can be sampled with 400 neighbors without suffering from the pairing instability. The code includes improvements for modeling giant impacts such as an interface/free-surface correction and a generalized EOS interface to use state-of-the-art equations of state. The code shows excellent scaling on HPC systems with either CPU based or hybrid CPU/GPU architecture, enabling the use of several billion particles in a simulation.
To simulate Jupiter’s post-impact evolution, we use a modified version of the Modules for Experiments in Stellar Astrophysics code [6]. We use 1D heavy-element fraction profiles extracted from the SPH results and imprint hot, warm and cold temperature profiles. We then evolve all these models for 4.56 Gyr, predicting Jupiter’s current-day composition profiles.
Results: We find that impacts of large embryos on growing Jupiter are unlikely and if an impact happens, it is very likely at an oblique angle, not head-on. This is in stark contrast to the findings of [1] who found that head-on impacts are rather likely to occur during Jupiter’s growth.
We simulate this oblique impact, as well as a head-on and an intermediate impact with SPH to see the effect on the core-envelope structure. The oblique impact does not disrupt the core and even though some impactor material gets mixed into the envelope, most of the mass coalesces onto the core (see Figure 2). In the head-on (see Figure 3) and intermediate impact, the core is fully or partially disrupted, but, in all cases, the heavy elements quickly settle in a massive pure heavy-element core which confirms the findings of [2]. Parts of the heavy elements, especially those originating in the impactor are strongly shock- and compression heated, leading to a very hot core.
The thermal evolution simulations show that when considering reasonable interior temperatures for Jupiter post-impact, giant impacts do not lead to an extended dilute core as inferred by interior models. Convective mixing tends to homogenize the planetary envelope, leaving a distinct compact core (see Figure 4).
Conclusions: We explored the possibility that Jupiter’s fuzzy core is the result of a giant impact. We find that giant impacts on growing Jupiter are unlikely and rather oblique. Such an impact is not able to disturb Jupiter’s core enough to create a fuzzy core. Even in a head-on impact, no fuzzy core remains. If a fuzzy core were formed by a GI, the thermal evolution would quickly result in a homogeneous envelope with a compact core. Jupiter’s fuzzy core has thus not formed via a giant impact. The formation is likely related to Jupiter’s formation history, which also more naturally explains why Saturn also has a fuzzy core.
Figure 1: Probability for a collision occurring during Jupiter’s growth.
Figure 2: Density slices through the oblique collision with 10^9 particles with sidelength of 50 R⊕.
Figure 3: Density slices through the head-on collision with 10^9 particles with sidelength of 50 R⊕.
Figure 4: Heavy-element fraction after the impact and after the post-impact evolution.
References:
[1] Liu, S.-F. et al. Nature 572, 355–357 (2019).
[2] Sandnes, T. D., Eke, V. R., Kegerreis, J. A., Massey, R. J. & Teodoro, L. F. A. https://doi.org/10.48550/arXiv.2412.06094 (2024).
[3] Shibata, S. & Helled, R. A&A 689, A26 (2024).
[4] Shibata, S., Helled, R. & Kobayashi, H. Monthly Notices of the Royal Astronomical Society 519, 1713–1731 (2023).
[5] Potter, D., Stadel, J. & Teyssier, R. Comput. Astrophys. 4, 2 (2017).
[6] Müller, S. & Helled, R. ApJ 967, 7 (2024).
How to cite: Meier, T., Reinhardt, C., Shibata, S., Mülller, S., Stadel, J., and Helled, R.: On the origin of Jupiter’s fuzzy core: constraints from N-body, impact, and evolution simulations, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-461, https://doi.org/10.5194/epsc-dps2025-461, 2025.
JunoCam images show a stable and approximately irrotational north polar cyclone, surrounded by eight circumpolar cyclones (CPCs) (Figure 1). The CPCs have been essentially stable over almost a decade since their discovery in 2016. They show only a minor zonal drift. Some of the CPCs develop and maintain a counter-rotating core that remains sustained over several months or longer. Those CPCs show a much stronger signature in MWR data than CPCs without a large embedded counter-rotating vortex. Between the north polar cyclone and the surrounding CPCs, up to about two additional large anti-cyclones occur that are not as stable or as long-lasting as the CPCs.
Figure 1: North polar CPC cluster seen by MWR and JunoCam. The north polar cyclone is nearly invisible in MWR data. CPCs with counter-rotating core tend to be brighter in MWR.
We have used a two-layer fluid dynamical model. In its first 2D layer we have assumed a steady flow with a north polar cyclone surrounded by CPCs with an optional counter-rotating core. A coupled second 2D layer behaves like an incompressible Euler flow, except for its coupling defined by a vorticity flux proportional to the vorticity difference between the two layers. This model develops almost no vertical vorticity flux for the north polar cyclone, but more vorticity flux for CPCs with a counter-rotating core than for those without such a feature, see Figure 2.
How to cite: Eichstädt, G., Brueshaber, S., Li, C., Levin, S., Brown, S., Orton, G., Rogers, J., Hansen-Koharcheck, C., and Bolton, S.: An empirical three-layer fluid dynamical model for a combined JunoCam and MWR snapshot of Jupiter's north polar region, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-438, https://doi.org/10.5194/epsc-dps2025-438, 2025.