Evidence for a Dichotomy in the Interior Structures of Jupiter and Saturn from Helium Phase Separation

Mankovich, Christopher; Fortney, Jonathan J.

doi:10.3847/1538-4357/ab6210

Cited by 40 publications

(56 citation statements)

References 75 publications

(162 reference statements)

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“…These abundances are compatible with constraints from Cassini UVIS/CIRS data [73]. They exceed predictions from models that made a more detailed accounting of H-He immiscibility [32,74,75] but considered only simplistic heavy element distributions.…”

Section: Methodssupporting

confidence: 75%

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A diffuse core in Saturn revealed by ring seismology

Mankovich

Fuller

2021

Nat Astron

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The best constraints on the internal structures of giant planets have historically come from measurements of their gravity fields [1,2,3]. These gravity data are inherently mostly sensitive to a planet's outer regions, providing only loose constraints on the deep interiors of Jupiter [2,4,5] and Saturn [6,7]. This fundamental limitation stymies efforts to measure the mass and compactness of these planets' cores, crucial properties for understanding their formation pathways and evolution [8,9]. However, studies of Saturn's rings have revealed waves driven by pulsation modes within Saturn [10,11,12,13], offering independent seismic probes of Saturn's interior [14,15,16]. The observations reveal gravity mode (g mode) pulsations which indicate that a part of Saturn's interior is stably stratified by composition gradients, and the g mode frequencies directly probe the buoyancy frequency within the planet [15]. Here, we compare structural models with gravity and seismic measurements to show that the data can only be explained by a diffuse, stably stratified core-envelope transition region in Saturn extending to approximately 60% of the planet's radius and containing approximately 17 Earth masses of ice and rock. The gradual distribution of heavy elements constrains mixing processes at work in Saturn, and it may reflect the planet's primordial structure and accretion history.Measurements of Jupiter's even zonal gravity harmonics J 2n (n = 1, 2, . . .) by the Juno spacecraft have raised the possibility of a gradual core-envelope transition within Jupiter [4,17]. At Saturn, the gravity field measured by the Cassini spacecraft is complicated by the large contribution from deep zonal flows [3,18,19], and disentangling these dynamical contributions from those of the rigidly rotating deep interior remains an outstanding challenge for understanding Saturn's deep structure. While it is known that Saturn's lowdegree gravity harmonics require some form of central density enhancement in Saturn[20], it is unknown to what extent this enhancement takes the form of a compact core versus a diffuse core structure akin to the one proposed for Jupiter. Furthermore, gravity data offer no direct information about the phase (fluid vs. solid) or stratification (mixed by convection

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Section: Methodssupporting

confidence: 75%

“…2) similarly assume a sigmoid profile for Y (r). The deep He mass fraction Y in is a free parameter; values of approximately 95% are predicted for the He-rich phase in Saturn's deep interior [74,75]. Y out is varied during ToF iterations to achieve a bulk He to H ratio Y = 0.275 representing that of the protosolar nebula [76].…”

Section: Methodsmentioning

confidence: 99%

A diffuse core in Saturn revealed by ring seismology

Mankovich

Fuller

2021

Nat Astron

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“…Second, Jovian adiabats for different H/He EOSs tend to intersect with H/He demixing curves at best in a small region at 1-3 Mbar. At present, only the rather cool MH13 EOS-based Jupiter adiabat for 166.1 K shows a clear intersection by about 450 K (Hubbard & Militzer 2016) with the state-of-the-art first-principles-based H/He demixing curve of Morales et al (2013), while the intersection with the lower demixing curve T dmx (P) of Schoettler & Redmer (2018) is only marginal (Mankovich & Fortney 2021). Since enhancing T 1 bar from the Galileo value of 166.1 K by only 14 K leads to an enhancement by ∼350 K at 1 Figure 5.…”

Section: Models For Enhanced 1 Bar Temperaturementioning

confidence: 79%

“…Adjusting the local He abundance to the local P-T conditions along the phase boundary yields an approximately linear increase in Y; however, the gradient and width of the He-rain region depend on the temperature profile assumed therein (Nettelmann et al 2015), which may range in Jupiter from adiabatic to modest superadiabaticity (Mankovich & Fortney 2021). A recent analysis of reflectivity data obtained for H/He samples that were precompressed to 2-4 GPa in diamond anvil cells and further shockcompressed to 60-180 GPa using the OMEGA layer indicates that an even larger portion of the Jupiter adiabat may intersect with the H/He phase boundary, as at the highest pressure where evidence of demixing is seen, 150 GPa, the measured temperatures were 10,000 K (Brygoo et al 2021).…”

Section: Jupiter Modelsmentioning

confidence: 99%

Theory of Figures to the Seventh Order and the Interiors of Jupiter and Saturn

Nettelmann

Movshovitz

et al. 2021

Planet. Sci. J.

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Interior modeling of Jupiter and Saturn has advanced to a state where thousands of models are generated that cover the uncertainty space of many parameters. This approach demands a fast method of computing their gravity field and shape. Moreover, the Cassini mission at Saturn and the ongoing Juno mission delivered gravitational harmonics up to J 12. Here we report the expansion of the theory of figures, which is a fast method for gravity field and shape computation, to the seventh order (ToF7), which allows for computation of up to J 14. We apply three different codes to compare the accuracy using polytropic models. We apply ToF7 to Jupiter and Saturn interior models in conjunction with CMS-19 H/He equation of state. For Jupiter, we find that J 6 is best matched by a transition from an He-depleted to He-enriched envelope at 2–2.5 Mbar. However, the atmospheric metallicity reaches 1 × solar only if the adiabat is perturbed toward lower densities, or if the surface temperature is enhanced by ∼14 K from the Galileo value. Our Saturn models imply a largely homogeneous-in-Z envelope at 1.5–4 × solar atop a small core. Perturbing the adiabat yields metallicity profiles with extended, heavy-element-enriched deep interior (diffuse core) out to 0.4 R Sat, as for Jupiter. Classical models with compact, dilute, or no core are possible as long as the deep interior is enriched in heavy elements. Including a thermal wind fitted to the observed wind speeds, representative Jupiter and Saturn models are consistent with all observed J n values.

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“…Cooler planets were considered using a curve constant entropy of S = 7.2 k B /el, which is the condition for the onset of helium rain as shown in Figure 1. The temperature for this "cold" curve is then defined by the reported effective temperatures for Jupiter and Saturn at the onset of helium rain by Mankovich & Fortney (2020). However, planets with lower incoming stellar energy flux are likely to be further from the assumed equilibrium state.…”

Section: Results For Selected Exoplanetsmentioning

confidence: 99%

Tidal Response and Shape of Hot Jupiters

Wahl

Thorngren

et al. 2021

ApJ

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We study the response of hot Jupiters to a static tidal perturbation using the concentric MacLaurin spheroid method. For strongly irradiated planets, we first performed radiative transfer calculations to relate the planet’s equilibrium temperature, T eq, to its interior entropy. We then determined the gravity harmonics, shape, moment of inertia, and static Love numbers for a range of two-layer interior models that assume a rocky core plus a homogeneous and isentropic envelope composed of hydrogen, helium, and heavier elements. We identify general trends and then study HAT-P-13b, the WASP planets 4b, 12b, 18b, 103b, and 121b, and Kepler-75b and CoRot-3b. We compute the Love numbers, k nm , and transit radius correction, ΔR, which we compare with predictions in the literature. We find that the Love number, k 22, of tidally locked giant planets cannot exceed a value of 0.6, and that the high T eq consistent with strongly irradiated hot Jupiters tends to further lower k 22. While most tidally locked planets are well described by a linear regime response of k 22 = 3J 2/q 0 (where q 0 is the rotation parameter of the gravitational potential), for extreme cases such as WASP-12b, WASP-103b, and WASP-121b, nonlinear effects can account for over 10% of the predicted k 22. The k 22 values larger than 0.6, as they have been reported for planets WASP-4b and HAT-P13B, cannot result from a static tidal response without extremely rapid rotation and thus are inconsistent with their expected tidally locked state.

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Evidence for a Dichotomy in the Interior Structures of Jupiter and Saturn from Helium Phase Separation

Cited by 40 publications

References 75 publications

A diffuse core in Saturn revealed by ring seismology

A diffuse core in Saturn revealed by ring seismology

Theory of Figures to the Seventh Order and the Interiors of Jupiter and Saturn

Tidal Response and Shape of Hot Jupiters

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