Jupiter’s Formation and Its Primordial Internal Structure

Abstract

The composition of Jupiter and the primordial distribution of the heavy elements are determined by its formation history. As a result, in order to constrain the primordial internal structure of Jupiter the growth of the core and the deposition and settling of accreted planetesimals must be followed in detail. In this paper we determine the distribution of the heavy elements in proto-Jupiter and determine the mass and composition of the core. We find that while the outer envelope of proto-Jupiter is typically convective and has an homogeneous composition, the innermost regions have compositional gradients. In addition, the existence of heavy elements in the envelope leads to much higher internal temperatures (several times 10 4 K) than in the case of a hydrogen-helium envelope. The derived core mass depends on the actual definition of the core: if the core is defined as the region in which the heavy-element mass fraction is above some limit (say 0.5), then it can be much more massive (∼ 15 M ⊕ ) and more extended (10% of the planet's radius) than in the case where the core is just the region with 100% heavy elements. In the former case Jupiter's core also consists of hydrogen and helium. Our results should be taken into account when constructing internal structure models of Jupiter and when interpreting the upcoming data from the Juno (NASA) mission.Subject headings: planets and satellites: individual (Jupiter) -planets and satellites:interiors -planets and satellites: composition -planets and satellites: formation -planets and satellites: gaseous planets 1

The Fuzziness of Giant Planets’ Cores

“…Note that this is different from the model of Lozovsky et al (2017), where the regions with composition gradients that were found to be convective according to the Ledoux convection criteria were assumed to homogenize instantaneously due to mixing. However, homogenizing convective regions with composition gradients requires a fairly long time 10 10 years 7 9  -formation timescale (see Vazan et al 2016).…”

Comparing Jupiter interior structure models to Juno gravity measurements and the role of a dilute core

“…In the canonical model for the formation of Jupiter, a dense core composed ∼10 M ⊕ (Earth masses) of rocky and icy material forms first, followed by a period of rapid runaway accretion of nebular gas [ Mizuno et al , ; Bodenheimer and Pollack , ; Pollack et al , ]. Recent formation models suggest that even in the core accretion scenario, the core can be small (∼2 M ⊕ ) or be diffused with the envelope [ Venturini et al , ; Lozovsky et al , ]. If Jupiter is formed by gravitational instability, i.e., the collapse of a region of the disk under self‐gravity [ Boss , ], there is no requirement for a core, although a core could still form at a later stage [ Helled et al , ].…”

Characterization of exoplanets from their formation

“…A more definitive answer will however require a fully self-consistent treatment of the problem which is not trivial (non-spherical symmetry of the impacts and thus mass deposition, modification of the EOS, local variation of the opacity, transport processes under the influence of compositional gradients, etc). However, such studies are important given the significant implications for the formation and evolution itself (e.g., Venturini et al 2016;Vazan et al 2016;Lozovsky et al 2017) as well as for the detectability via direct imaging.…”

“…First works have recently started to study the compositional aspect (Venturini et al 2016;Lozovsky et al 2017), but they do not yet address the consequences for the luminosity. Because of this, it is currently also not clear if, for the core-mass effect to work efficiently, a high total heavy element content today (in the envelope and/or core) is sufficient as implicitly assumed in the argument above.…”

“…It is clear the future work will have to investigate this in a self-consistent fashion (see Venturini et al 2016;Lozovsky et al 2017, for works that do this for the composition of protoplanets without addressing the luminosity and the solid accretion during gas runaway, though.). First, we assess whether much less potential energy is liberated as L pla,mix by planetesimals that mix throughout the envelope instead of sinking, i.e., whether we are greatly overestimating the heating by impacting planetesimals L pla that in the sinking approximation we use in the syntheses is given approximately by…”