# The fuzziness of giant planets' cores

## TL;DR

This paper explores how the internal structure of giant planets, especially their cores, depends on formation conditions and growth rates, suggesting that cores may not be distinct and could have gradual heavy-element distributions.

## Contribution

It introduces a model linking planetary growth rates and heavy-element distribution, challenging the traditional core-envelope separation concept in giant planets.

## Key findings

- Core structure depends on accretion ratios and nebula conditions.
- Jupiter's core may be indistinct and contain mixed elements.
- Gravitational measurements can constrain core properties.

## Abstract

Giant planets are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen-helium envelope is applied in both formation and structure models. We show that the primordial internal structure depends on the planetary growth rate, in particular, the ratio of heavy elements accretion to gas accretion. For a wide range of likely conditions, this ratio is in one-to-one correspondence with the resulting post-accretion profile of heavy elements within the planet. This flux ratio depends sensitively on the assumed solid surface density in the surrounding nebula. We suggest that giant planets' cores might not be distinct from the envelope and includes some hydrogen and helium, and the deep interior can have a gradual heavy-element structure. Accordingly, Jupiter's core may not be well-defined. Accurate measurements of Jupiter's gravitational field by Juno could put constraints on Jupiter's core mass. However, as we suggest here, the definition of Jupiter's core is complex, and the core's physical properties (mass, density) depend on the actual definition of the core and on its growth history.