Context. Reconciling models of Jupiter’s interior with measurements of the atmospheric composition still poses a significant challenge. Interior models favour a subsolar or solar abundance of heavy elements, Z, whereas atmospheric measurements suggest a supersolar abundance. One potential solution may be to account for the presence of an inverted Z gradient, namely, an inward decrease of Z, which implies a higher heavy-element abundance in the atmosphere than in the outer envelope.
Aims: We investigate two scenarios in which the inverted Z gradient is either located at levels where helium rain occurs (∼Mbar) or at higher levels (∼kbar) where a radiative region could exist. Here, we aim to assess the plausibility of these scenarios.
Methods: We calculated interior and evolution models of Jupiter with such an inverted Z gradient and we set constraints on its stability and formation.
Results: We find that an inverted Z gradient at the location of helium rain is not feasible, as it would require a late accretion and would involve too much material. We find interior models with an inverted Z gradient at upper levels due to a radiative zone preventing downward mixing, could satisfy the current gravitational field of the planet. However, our evolution models suggest that this second scenario cannot be validated.
Conclusions: We find that an inverted Z gradient in Jupiter could indeed be stable, however, its presence either at the Mbar or kbar levels is rather unlikely.
