Further constraints on Jupiter's primordial structure

TL;DR

This study integrates a dynamical constraint from Jupiter's inner moons with thermal-evolution modeling to constrain Jupiter's primordial interior. By generating and evolving 4,250 initial structures using a MESAs-based planetary interior code, and applying a primordial constraint from the Io–Amalthea–Thebe system, the authors identify viable initial states that evolve into the present-day Jupiter, revealing a warm, metal-rich dilute core and a warm envelope with a primordial radius near $1.89\,R_J$. The dynamical constraint breaks degeneracies between thermal and compositional structure, pointing to most heavy elements being accreted early during runaway gas accretion and constraining the energy dissipated at the accretion shock. The results emphasize Jupiter as a dynamically informed, stratified gas giant and demonstrate the value of combining formation-era constraints with interior evolution for understanding giant planet formation and evolution.

Abstract

The primordial structure of Jupiter remains uncertain, yet it holds vital clues on the planet's formation and early evolution. Recent work used dynamical constraints from Jupiter's inner moons to determine its primordial state, thereby providing a novel, formation-era anchor point for interior modeling. Building on this approach, we combine these dynamical constraints with thermal evolution simulations to investigate which primordial structures are consistent with present-day Jupiter. We present 4,250 evolutionary models of the planetary structure, including compositional mixing and helium phase separation, spanning a broad range of initial entropies and composition profiles. We find that Jupiter's present-day structure is best explained by a warm ($4.98_{-2.57}^{+3.00}\, \mathrm{k_B\, m_u^{-1}}$), metal-rich dilute core inherited from formation. To simultaneously satisfy constraints on Jupiter's primordial spin, however, its envelope must have been significantly warmer ($9.32_{-0.58}^{+0.48}\, \mathrm{k_B\, m_u^{-1}}$) at the time of disk dispersal. We determine Jupiter's primordial radius to be $1.89_{-0.49}^{+0.40}\, \mathrm{R_J}$. These results provide new constraints on Jupiter's formation, suggesting that most heavy elements were accreted early during runaway gas accretion, and placing bounds on the energy dissipated during the accretion shock.

Figures (6)

• Figure 1: Primordial heavy-element mass fraction (top left), specific entropy (top right), specific potential entropy (bottom left), and temperature (bottom right) as a function of mass for 4,250 randomly generated Jupiter models. The color scale indicates the quality of the fit to Jupiter's present-day structure. The black solid lines represent our best-fit model that fulfills Eq. \ref{['eq:BA_2025']}. The black dotted line represents the best-fit model without applying the BA2025 constraint.
• Figure 2: Time evolution of the mean radius (top left), 1 bar temperature (top right), J$_2$ (bottom left), and J$_4$ (bottom right) compared to present-day Jupiter (dashed red line). The line colors are the same as in Fig. \ref{['fig:initial_profiles']}.
• Figure 3: Time evolution of normalized moment of inertia vs. radius for the sample of randomly generated Jupiter models. The line colors are the same as in Fig. \ref{['fig:initial_profiles']}. The colored regions indicate the primordial constraint of Eq. \ref{['eq:BA_2025']}, where the labels indicate the resonance of Io with Amalthea (A) or Thebe (T), respectively. The black triangles mark Jupiter's present-day radius and NMoI as estimated by Helled2011 and Ni2018, respectively. The black square corresponds to the initial model from Sur2025..
• Figure 4: Distributions of core entropy (left) and envelope entropy (right) before relaxing the composition gradient (i.e., at proto-solar composition) for models matching present-day Jupiter within 10. Colors of the stacked histogram indicate whether or not the primordial constraint of BA2025 is fulfilled. Best-fit values for the constrained models are marked at the center of each panel.
• Figure 5: Primordial heavy-element mass fraction (solid lines) and entropy (dotted lines) for the five best-fitting models that satisfy Eq. \ref{['eq:BA_2025']}.