The origin of Jupiter's fuzzy core

Abstract:

The Juno mission has revolutionized and challenged our understanding of Jupiter. Now, with the prime mission close to completion, we can already assess the lessons we have learned about Jupiter’s formation and evolution. Structure models of Jupiter that fit Juno’s gravity data imply that the planet has compositional gradients and is accordingly non-adiabatic, with a complex internal structure. As a result, formation and evolution models of Jupiter must be adjusted.

I will discuss potential formation and evolution paths that can lead to an internal structure model consistent with Juno data, and their limitations. I will show that formation models including the heavy-element enrichment during the planetary growth indeed predict that Jupiter’s primordial internal structure is likely to be inhomogeneous, with composition gradients in its deep interior. However, typically this region which could be interpreted as a primordial dilute core is confined to ∼10% of Jupiter’s total mass, while structure models that fit Juno data imply that this region consist 30% of the mass or more. It is possible to explain Jupiter's extended dilute core by a relatively long (~2 Myrs) formation phase where the growing proto-Jupiter accretes gas and planetesimals delaying the runaway gas accretion. Alternatively, Jupiter’s fuzzy core might be a result of a giant impact. Both of these suggested scenarios require somewhat special and specific conditions. Clearly more research is needed before we can take full advantage of Juno data, and this is still work in progress. Since Jupiter is used as a prototype for gas giant planets these findings also reflect on our understanding of the formation, evolution and interiors of Saturn and giant exoplanets.