(Un)stable Jupiter models with CD21 H/He-EOS

The atmospheric metallicity Z_atm of Jupiter inferred from interior models responds sensitively to assumed uncertainties in the H/He equation of state at around 10-50 GPa pressure levels and the 1-bar outer boundary temperature [1,2]. If an adiabatic temperature profile and 166 K 1-bar temperature is assumed, a perturbation toward lower densities in the 10-50 GPa region seems required for most H/He-EOSs, in order match the JUNO's gravitational harmonic J₄ value with >1x solar atmospheric  metallicity. In contrast, Galileo and JUNO measurements revealed higher atmospheric enrichments in the noble gases and ammonia of 2-3x solar. Yet for water, current uncertainties still permit lower than 1x solar in Jupiter's equatorial atmosphere [3]. 

Here, we adopt the recently proposed H/He-EOS CD21 [4] to compute a series of Jupiter interior models. We show that CD21-EOS based adiabats are less dense at ~20 GPa while denser at ~2 GPa as compared to the CMS19 H/He-EOS. The CD21 EOS allows us to lift the atmospheric metallicity by a ΔZ_atm ~1x solar when fitting J₄, while its denser behavior at 2 GPa moves the models away from the formerly good fit to J₆ that was possible with CMS19 EOS [1].

As our adiabatic models yield too low atmospheric metallicities, we insert an outer stable region, as recently suggested to explain Jupiter's magnetic field [5]. We find that a super-adiabatic stable region should occur at ~1 GPa or farther out in order to noticably influence the density in the ~50 GPa region. However, our models suggest that an outer stable region alone is insufficient to enhance the metallicity to 1x solar. Therefore, we vary in addition the 1-bar surface temperature toward warmer interiors as indicated by recent re-analysis of Voyager remote sensing data.

Overall, this work aims at predicting Jupiter's deep water abundance for comparison against formation models [6] and JUNO observations. 

[1] Nettelmann, Movshovitz, Ni et al, PSJ 2:241 (2021) 
[2] Miguel Y, Bazot M, Guillot T et al, AA 662:A18 (2022) 
[3] Li Ch, Ingersoll A, Bolton S et al, NatAst 4:609 (2020) 
[4] Chabrier G, Debras F, ApJ 917:4 
[5] Moore KM, Barik A, Stanley S, et al, JGR Planets 127:e2022JE007479 (2022)
[6] Helled R, Stevenson DJ, Lunine J, et al, Icarus 378:114937 (2022)