The Nature and Composition of Jupiter’s Building Blocks Derived from the Water Abundance Measurements by the Juno Spacecraft

Abstract

The microwave radiometer on board the Juno spacecraft provided a measurement of the water abundance found to range between ∼1 and 5.1 times the protosolar abundance of oxygen in the near-equatorial region of Jupiter. Here, we aim to combine this up-to-date oxygen determination, which is likely to be more representative of the bulk abundance than the Galileo probe subsolar value, with the other known measurements of elemental abundances in Jupiter, to derive the formation conditions and initial composition of the building blocks agglomerated by the growing planet, and that determine the heavy element composition of its envelope. We investigate several cases of formation of icy solids in the protosolar nebula (PSN), from the condensation of pure ices to the crystallization of mixtures of pure condensates and clathrates in various proportions. Each of these cases corresponds to a distinct solid composition whose amount is adjusted in the envelope of Jupiter to match the O abundance measured by Juno. The volatile enrichments can be matched by a wide range of planetesimal compositions, from solids exclusively formed from pure condensates or from nearly exclusively clathrates, the latter case providing a slightly better fit. The total mass of volatiles needed in the envelope of Jupiter to match the observed enrichments is within the ∼4.3–39 M ⊕ range, depending on the crystallization scenario considered in the PSN. A wide range of masses of heavy elements derived from our fits is found to be compatible with the envelope’s metallicity calculated from current interior models.